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Maven: The Definitive Guide by Sonatype Company

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Chapter 4. Customizing a Maven Project

Introduction

This chapter expands on the information introduced in Chapter 3. We’re going to create a simple project generated with the Maven Archetype plugin, add some dependencies, add some source code, and customize the project to suit our needs. By the end of this chapter, you will know how to start using Maven to create real projects.

Downloading This Chapter’s Example

We’ll be developing a useful program that interacts with a Yahoo! Weather web service. Although you should be able to follow along with this chapter without the example source code, we recommend that you download a copy of the code to use as a reference. This chapter’s example project may be downloaded with the book’s example code at http://www.sonatype.com/book/mvn-examples-1.0.zip or http://www.sonatype.com/book/mvn-examples-1.0.tar.gz. Unzip this archive in any directory, and then go to the ch04/ directory. There you will see a directory named simple-weather/, which contains the Maven project developed in this chapter. If you wish to follow along with the example code in a web browser, go to http://www.sonatype.com/book/examples-1.0 and click on the ch04/ directory.

Defining the Simple Weather Project

Before we start customizing this project, let’s take a step back and talk about the simple weather project. What is it? It’s a contrived example, created to demonstrate some of the features of Maven. It is an application that is representative of the kind you might need to build. The simple weather application is a basic command-line-driven application that takes a zip code and retrieves some data from the Yahoo! Weather RSS feed. It then parses the result and prints the result to standard output.

We chose this example for a number of reasons. First, it is straightforward. A user supplies input via the command line, the app takes that zip code, makes a request to Yahoo! Weather, parses the result, and formats some simple data to the screen. This example is a simple main() function and some supporting classes; there is no enterprise framework to introduce and explain, just XML parsing and some logging statements. Second, it gives us a good excuse to introduce some interesting libraries such as Velocity, Dom4J, and Log4J. Although this book is focused on Maven, we won’t shy away from an opportunity to introduce interesting utilities. Lastly, it is an example that can be introduced, developed, and deployed in a single chapter.

Yahoo! Weather RSS

Before you build this application, you should know something about the Yahoo! Weather RSS feed. To start with, the service is made available under the following terms:

The feeds are provided free of charge for use by individuals and nonprofit organizations for personal, noncommercial uses. We ask that you provide attribution to Yahoo! Weather in connection with your use of the feeds.

In other words, if you are thinking of integrating these feeds into your commercial web site, think again—this feed is for personal, noncommercial use. The use we’re encouraging in this chapter is personal educational use. For more information about these terms of service, see the Yahoo Weather! API documentation here: http://developer.yahoo.com/weather/.

Creating the Simple Weather Project

First, let’s use the Maven Archetype plugin to create a basic skeleton for the simple weather project. Execute the following command to create a new project:

$ mvn archetype:create -DgroupId=org.sonatype.mavenbook.ch04 \
                                         -DartifactId=simple-weather \
                                         -DpackageName=org.sonatype.mavenbook \
                                         -Dversion=1.0
[INFO] [archetype:create]
[INFO] artifact org.apache.maven.archetypes:maven-archetype-quickstart: \
       checking for updates from central
[INFO] ------------------------------------------------------------------
[INFO] Using following parameters for creating Archetype: \
       maven-archetype-quickstart:RELEASE
[INFO] ------------------------------------------------------------------
[INFO] Parameter: groupId, Value: org.sonatype.mavenbook.ch04
[INFO] Parameter: packageName, Value: org.sonatype.mavenbook
[INFO] Parameter: basedir, Value: ~/examples
[INFO] Parameter: package, Value: org.sonatype.mavenbook
[INFO] Parameter: version, Value: 1.0
[INFO] Parameter: artifactId, Value: simple-weather
[INFO] *** End of debug info from resources from generated POM ***
[INFO] Archetype created in dir: ~/examples/simple-weather

Once the Maven Archetype plugin creates the project, go into the simple-weather directory and take a look at the pom.xml file. You should see the XML document that’s shown in Example 4-1.

Example 4-1. Initial POM for the simple-weather project
<project xmlns="http://maven.apache.org/POM/4.0.0" 
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 
                      http://maven.apache.org/maven-v4_0_0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>org.sonatype.mavenbook.ch04</groupId>
  <artifactId>simple-weather</artifactId>
  <packaging>jar</packaging>
  <version>1.0</version>
  <name>simple-weather2</name>
  <url>http://maven.apache.org</url>
  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>
  </dependencies>
  <build>
    <plugins>
      <plugin>
        <artifactId>maven-compiler-plugin</artifactId>
        <configuration>
          <source>1.5</source>
          <target>1.5</target>
        </configuration>
      </plugin>
    </plugins>
  </build>
</project>

Notice that we passed in the version parameter to the archetype:create goal. This overrides the default value of 1.0-SNAPSHOT. In this project, we’re developing the 1.0 version of the simple-weather project, as you can see in the pom.xml version element.

Customize Project Information

Before we start writing code, let’s customize the project information a bit. We want to add some information about the project’s license, the organization, and a few of the developers associated with the project. This is all standard information you would expect to see in most projects. Example 4-2 shows the XML that supplies the organizational information, the licensing information, and the developer information.

Example 4-2. Adding organizational, legal, and developer information to the pom.xml
<project xmlns="http://maven.apache.org/POM/4.0.0" 
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 
                      http://maven.apache.org/maven-v4_0_0.xsd">
...

  <name>simple-weather</name>
  <url>http://www.sonatype.com</url>

  <licenses>
    <license>
      <name>Apache 2</name>
      <url>http://www.apache.org/licenses/LICENSE-2.0.txt</url>
      <distribution>repo</distribution>
      <comments>A business-friendly OSS license</comments>
    </license>
  </licenses>

  <organization>
    <name>Sonatype</name>
    <url>http://www.sonatype.com</url>
  </organization>

  <developers>
    <developer>
      <id>jason</id>
      <name>Jason Van Zyl</name>
      <email>jason@maven.org</email>
      <url>http://www.sonatype.com</url>
      <organization>Sonatype</organization>
      <organizationUrl>http://www.sonatype.com</organizationUrl>
      <roles>
        <role>developer</role>
      </roles>
      <timezone>-6</timezone>
    </developer>
  </developers>
...
</project>

The ellipses in this example are shorthand for an abbreviated listing. Whenever you see a pom.xml with “...” directly after the project element’s start tag and directly before the end tag, it indicates that we are not showing the entire pom.xml file. In this case, the licenses, organization, and developers elements are all added before the dependencies element.

Add New Dependencies

The simple weather application will need to complete the following three tasks: retrieve XML data from Yahoo! Weather, parse the XML from Yahoo, and then print formatted output to standard output. To accomplish these tasks, we have to introduce some new dependencies to our project’s pom.xml. To parse the XML response from Yahoo!, we’ll use Dom4J and Jaxen; to format the output of this command-line program, we’ll use Velocity; and we also need to add a dependency for Log4J, which we will be using for logging. After we add these dependencies, our dependencies element will look like Example 4-3.

Example 4-3. Adding Dom4J, Jaxen, Velocity, and Log4J as dependencies
<project>
  [...]
  <dependencies>
    <dependency>
      <groupId>log4j</groupId>
      <artifactId>log4j</artifactId>
      <version>1.2.14</version>
    </dependency>
    <dependency>
      <groupId>dom4j</groupId>
      <artifactId>dom4j</artifactId>
      <version>1.6.1</version>
    </dependency>
    <dependency>
      <groupId>jaxen</groupId>
      <artifactId>jaxen</artifactId>
      <version>1.1.1</version>
    </dependency>
    <dependency>
      <groupId>velocity</groupId>
      <artifactId>velocity</artifactId>
      <version>1.5</version>
    </dependency>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>
  </dependencies>
  [...]
</project>

As you can see, we’ve added four more dependency elements in addition to the existing element that was referencing the test-scoped dependency on JUnit. If you add these dependencies to the project’s pom.xml file and then run mvn install, you will see Maven downloading all of these dependencies and other transitive dependencies to your local Maven repository.

How did we find these dependencies? Did we just “know” the appropriate groupId and artifactId values? Some of the dependencies are so common (such as Log4J) that you’ll just remember what the groupId and artifactId are every time you need to use them. As for Velocity, Dom4J, and Jaxen, we located them using the very helpful web site http://www.mvnrepository.com. This site provides a search interface for the Maven repository that you can use to search for dependencies. To test this yourself, visit http://www.mvnrepository.com and search for some commonly used libraries such as Hibernate or the Spring Framework. When you search for an artifact on this site, it will show you an artifactId and all of the versions known to the central Maven repository. Clicking on the details for a specific version will load a page that contains the dependency element you’ll need to copy and paste into your own project’s pom.xml. If you need to find a dependency, you’ll want to check out http://www.mvnrepository.com, because you’ll often find that certain libraries have more than one groupId. With this tool, you can make sense of the Maven repository.

Simple Weather Source Code

The simple weather command-line application consists of the following five Java classes:

org.sonatype.mavenbook.weather.Main

The Main class contains a static main() function, and is the entry point for this system.

org.sonatype.mavenbook.weather.Weather

The Weather class is a straightforward Java bean that holds the location of our weather report and some key facts, such as the temperature and humidity.

org.sonatype.mavenbook.weather.YahooRetriever

The YahooRetriever class connects to Yahoo! Weather and returns an InputStream of the data from the feed.

org.sonatype.mavenbook.weather.YahooParser

The YahooParser class parses the XML from Yahoo! Weather, and returns a Weather object.

org.sonatype.mavenbook.weather.WeatherFormatter

The WeatherFormatter class takes a Weather object, creates a VelocityContext, and evaluates a Velocity template.

Although we won’t dwell on the code here, we will provide all the necessary code for you to get the example working. We assume that most readers have downloaded the examples that accompany this book, but we’re also mindful of those who may wish to follow the example in this chapter step-by-step. The sections that follow list classes in the simple-weather project. Each of these classes should be placed in the same package: org.sonatype.mavenbook.weather.

Let’s remove the App and the AppTest classes created by archetype:create and add our new package. In a Maven project, all of a project’s source code is stored in src/main/java. From the base directory of the new project, execute the following commands:

$ cd src/test/java/org/sonatype/mavenbook
$ rm AppTest.java
$ cd ../../../../../..
$ cd src/main/java/org/sonatype/mavenbook
$ rm App.java
$ mkdir weather
$ cd weather

This creates a new package named org.sonatype.mavenbook.weather. Now we need to put some classes in this directory. Using your favorite text editor, create a new file named Weather.java with the contents shown in Example 4-4.

Example 4-4. simple-weather’s Weather model object
package org.sonatype.mavenbook.weather;

public class Weather {
  private String city;
  private String region;
  private String country;
  private String condition;
  private String temp;
  private String chill;
  private String humidity;
    
  public Weather() {}

  public String getCity() { return city; }
  public void setCity(String city) { this.city = city; }

  public String getRegion() { return region; }
  public void setRegion(String region) { this.region = region; }

  public String getCountry() { return country; }
  public void setCountry(String country) { this.country = country; }

  public String getCondition() { return condition; }
  public void setCondition(String condition) { this.condition = condition; }

  public String getTemp() { return temp; }
  public void setTemp(String temp) { this.temp = temp; }
         
  public String getChill() { return chill; }
  public void setChill(String chill) { this.chill = chill; }

  public String getHumidity() { return humidity; }
  public void setHumidity(String humidity) { this.humidity = humidity; }
}

The Weather class defines a simple bean that is used to hold the weather information parsed from the Yahoo! Weather feed. This feed provides a wealth of information, from the sunrise and sunset times to the speed and direction of the wind. To keep this example as simple as possible, the Weather model object keeps track of only the temperature, chill, humidity, and a textual description of current conditions.

Now, in the same directory, create a file named Main.java. This Main class will hold the static main() function—the entry point for this example. See Example 4-5.

Example 4-5. simple-weather’s Main class
package org.sonatype.mavenbook.weather;

import java.io.InputStream;

import org.apache.log4j.PropertyConfigurator;


public class Main {

  public static void main(String[] args) throws Exception {
    // Configure Log4J
    PropertyConfigurator.configure(Main.class.getClassLoader()
                                       .getResource("log4j.properties"));

    // Read the Zip Code from the Command-line (if none supplied, use 60202)
    String zipcode = "60202";
    try {
      zipcode = args[0]);
    } catch( Exception e ) {}

    // Start the program
    new Main(zipcode).start();
  }

  private String zip;

  public Main(String zip) {
    this.zip = zip;
  }

  public void start() throws Exception {
    // Retrieve Data
    InputStream dataIn = new YahooRetriever().retrieve( zip );

    // Parse Data
    Weather weather = new YahooParser().parse( dataIn );

    // Format (Print) Data
    System.out.print( new WeatherFormatter().format( weather ) );
  }
}

The main() function shown in this example configures Log4J by retrieving a resource from the classpath. It then tries to read a zip code from the command line. If an exception is thrown while it is trying to read the zip code, the program will default to a zip code of 60202. Once it has a zip code, it instantiates an instance of Main and calls the start() method on an instance of Main. The start() method calls out to the YahooRetriever to retrieve the weather XML. The YahooRetriever returns an InputStream, which is then passed to the YahooParser. The YahooParser parses the Yahoo! Weather XML and returns a Weather object. Finally, the WeatherFormatter takes a Weather object and spits out a formatted String, which is printed to standard output.

Create a file named YahooRetriever.java in the same directory with the contents shown in Example 4-6.

Example 4-6. simple-weather’s YahooRetriever class
package org.sonatype.mavenbook.weather;

import java.io.InputStream;
import java.net.URL;
import java.net.URLConnection;

import org.apache.log4j.Logger;

public class YahooRetriever {

  private static Logger log = Logger.getLogger(YahooRetriever.class);

  public InputStream retrieve(int zipcode) throws Exception {
    log.info( "Retrieving Weather Data" );
    String url = "http://weather.yahooapis.com/forecastrss?p=" + zipcode;
    URLConnection conn = new URL(url).openConnection();
    return conn.getInputStream();
  }
}

This simple class opens a URLConnection to the Yahoo! Weather API and returns an InputStream. To create something to parse this feed, we’ll need to create the YahooParser.java file in the same directory. See Example 4-7.

Example 4-7. simple-weather’s YahooParser class
package org.sonatype.mavenbook.weather;

import java.io.InputStream;
import java.util.HashMap;
import java.util.Map;

import org.apache.log4j.Logger;
import org.dom4j.Document;
import org.dom4j.DocumentFactory;
import org.dom4j.io.SAXReader;

public class YahooParser {

  private static Logger log = Logger.getLogger(YahooParser.class);

  public Weather parse(InputStream inputStream) throws Exception {
    Weather weather = new Weather();
  
    log.info( "Creating XML Reader" );
    SAXReader xmlReader = createXmlReader();
    Document doc = xmlReader.read( inputStream );

    log.info( "Parsing XML Response" );
    weather.setCity( doc.valueOf("/rss/channel/y:location/@city") );
    weather.setRegion( doc.valueOf("/rss/channel/y:location/@region") );
    weather.setCountry( doc.valueOf("/rss/channel/y:location/@country") );
    weather.setCondition( doc.valueOf("/rss/channel/item/y:condition/@text") );
    weather.setTemp( doc.valueOf("/rss/channel/item/y:condition/@temp") );
    weather.setChill( doc.valueOf("/rss/channel/y:wind/@chill") );
    weather.setHumidity( doc.valueOf("/rss/channel/y:atmosphere/@humidity") );
  
    return weather;
  }

  private SAXReader createXmlReader() {
    Map<String,String> uris = new HashMap<String,String>();
        uris.put( "y", "http://xml.weather.yahoo.com/ns/rss/1.0" );
        
    DocumentFactory factory = new DocumentFactory();
    factory.setXPathNamespaceURIs( uris );
        
    SAXReader xmlReader = new SAXReader();
    xmlReader.setDocumentFactory( factory );
    return xmlReader;
  }
}

The YahooParser is the most complex class in this example. We’re not going to dive into the details of Dom4J or Jaxen here, but the class deserves some explanation. YahooParser’s parse() method takes an InputStream and returns a Weather object. To do this, it needs to parse an XML document with Dom4J. Since we’re interested in elements under the Yahoo! Weather XML namespace, we need to create a namespace-aware SAXReader in the createXmlReader() method. Once we create this reader and parse the document, we get an org.dom4j.Document object back. Instead of iterating through child elements, we simply address each piece of information we need using an XPath expression. Dom4J provides the XML parsing in this example, and Jaxen provides the XPath capabilities.

Once we’ve created a Weather object, we need to format our output for human consumption. Create a file named WeatherFormatter.java in the same directory as the other classes. See Example 4-8.

Example 4-8. simple-weather’s WeatherFormatter class
package org.sonatype.mavenbook.weather;

import java.io.InputStreamReader;
import java.io.Reader;
import java.io.StringWriter;

import org.apache.log4j.Logger;
import org.apache.velocity.VelocityContext;
import org.apache.velocity.app.Velocity;

public class WeatherFormatter {

  private static Logger log = Logger.getLogger(WeatherFormatter.class);

  public String format( Weather weather ) throws Exception {
    log.info( "Formatting Weather Data" );
    Reader reader = 
      new InputStreamReader( getClass().getClassLoader()
                                 .getResourceAsStream("output.vm"));
    VelocityContext context = new VelocityContext();
    context.put("weather", weather );
    StringWriter writer = new StringWriter();
    Velocity.evaluate(context, writer, "", reader);
    return writer.toString();
  }
}

The WeatherFormatter uses Velocity to render a template. The format() method takes a Weather bean and spits out a formatted String. The first thing the format() method does is load a Velocity template from the classpath named output.vm. We then create a VelocityContext, which is populated with a single Weather object named weather. A StringWriter is created to hold the results of the template merge. The template is then evaluated with a call to Velocity.evaluate(), and the results are returned as a String.

Before we can run this example, we’ll need to add some resources to our classpath.

Add Resources

This project depends on two classpath resources: the Main class that configures Log4J with a classpath resource named log4j.properties, and the WeatherFormatter that references a Velocity template from the classpath named output.vm. Both of these resources need to be in the default package (or the root of the classpath).

To add these resources, we’ll need to create a new directory from the base directory of the project: src/main/resources. Since this directory was not created by the archetype:create task, we need to create it by executing the following commands from the project’s base directory:

$ cd src/main
$ mkdir resources
$ cd resources

Once the resources directory is created, we can add the two resources. First, add the log4j.properties file in the resources directory, as shown in Example 4-9.

Example 4-9. simple-weather’s Log4J configuration file
# Set root category priority to INFO and its only appender to CONSOLE.
log4j.rootCategory=INFO, CONSOLE

# CONSOLE is set to be a ConsoleAppender using a PatternLayout.
log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
log4j.appender.CONSOLE.Threshold=INFO
log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
log4j.appender.CONSOLE.layout.ConversionPattern=%-4r %-5p %c{1} %x - %m%n

This log4j.properties file simply configures Log4J to print all log messages to standard output using a PatternLayout. Lastly, we need to create the output.vm, which is the Velocity template used to render the output of this command-line program. Create output.vm in the resources/ directory. See Example 4-10.

Example 4-10. simple-weather’s output Velocity template
*********************************
 Current Weather Conditions for:
  ${weather.city}, ${weather.region}, ${weather.country}
  
 Temperature: ${weather.temp}
   Condition: ${weather.condition}
    Humidity: ${weather.humidity}
  Wind Chill: ${weather.chill}
*********************************

This template contains a number of references to a variable named weather, which is the Weather bean that was passed to the WeatherFormatter. The ${weather.temp} syntax is shorthand for retrieving and displaying the value of the temp bean property. Now that we have all of our project’s code in the right place, we can use Maven to run the example.

Running the Simple Weather Program

Using the Exec plugin from the Codehaus Mojo project, we can execute this program. To execute the Main class, run the following command from the project’s base directory:

$ mvn install
$ mvn exec:java -Dexec.mainClass=org.sonatype.mavenbook.weather.Main
...
[INFO] [exec:java]
0    INFO  YahooRetriever  - Retrieving Weather Data
134  INFO  YahooParser  - Creating XML Reader
333  INFO  YahooParser  - Parsing XML Response
420  INFO  WeatherFormatter  - Formatting Weather Data
*********************************
 Current Weather Conditions for:
  Evanston, IL, US
  
 Temperature: 45
   Condition: Cloudy
    Humidity: 76
  Wind Chill: 38
*********************************
...

We didn’t supply a command-line argument to the Main class, so we ended up with the default zip code, 60202. To supply a zip code, we would use the -Dexec.args argument and pass in a zip code:

$ mvn exec:java -Dexec.mainClass=org.sonatype.mavenbook.weather.Main \ 
     -Dexec.args="70112"
...
[INFO] [exec:java]
0    INFO  YahooRetriever  - Retrieving Weather Data
134  INFO  YahooParser  - Creating XML Reader
333  INFO  YahooParser  - Parsing XML Response
420  INFO  WeatherFormatter  - Formatting Weather Data
*********************************
 Current Weather Conditions for:
  New Orleans, LA, US
  
 Temperature: 82
   Condition: Fair
    Humidity: 71
  Wind Chill: 82
*********************************
[INFO] Finished at: Sun Aug 31 09:33:34 CDT 2008
...

As you can see, we’ve successfully executed the simple weather command-line tool, retrieved some data from Yahoo! Weather, parsed the result, and formatted the resulting data with Velocity. We achieved all of this without doing much more than writing our project’s source code and adding some minimal configuration to the pom.xml. Notice that no “build process” was involved. We didn’t need to define how or where the Java compiler compiles our source to bytecode, and we didn’t need to instruct the build system how to locate the bytecode when we executed the example application. All we needed to do to include a few dependencies was locate the appropriate Maven coordinates.

The Maven Exec Plugin

The Exec plugin allows you to execute Java classes and other scripts. It is not a core Maven plugin, but it is available from the Mojo project hosted by Codehaus. For a full description of the Exec plugin, run:

$ mvn help:describe -Dplugin=exec -Dfull

This will list all of the goals that are available in the Maven Exec plugin. The Help plugin will also list all of the valid parameters for the Exec plugin. If you would like to customize the behavior of the Exec plugin to pass in command-line arguments, you should use the documentation provided by help:describe as a guide. Although the Exec plugin is useful, you shouldn’t rely on it as a way to execute your application outside of running tests during development. For a more robust solution, use the Maven Assembly plugin that is demonstrated in the section Building a Packaged Command-Line Application,” later in this chapter.

Exploring Your Project Dependencies

The Exec plugin makes it possible for us to run the simplest weather program without having to load the appropriate dependencies into the classpath. In any other build system, we would have to copy all of the program dependencies into some sort of lib/ directory containing a collection of JAR files. Then, we would have to write a simple script that includes our program’s bytecode and all of our dependencies in a classpath. Only then could we run java org.sonatype.mavenbook.weather.Main. The Exec plugin leverages the fact that Maven already knows how to create and manage your classpath and dependencies.

This is convenient, but it’s also nice to know exactly what is being included in your project’s classpath. Although the project depends on a few libraries such as Dom4J, Log4J, Jaxen, and Velocity, it also relies on a few transitive dependencies. If you need to find out what is on the classpath, you can use the Maven Dependency plugin to print out a list of resolved dependencies. To print out this list for the simple weather project, execute the dependency:resolve goal:

$ mvn dependency:resolve
...
[INFO] [dependency:resolve]
[INFO] 
[INFO] The following files have been resolved: 
[INFO]    com.ibm.icu:icu4j:jar:2.6.1 (scope = compile)
[INFO]    commons-collections:commons-collections:jar:3.1 (scope = compile)
[INFO]    commons-lang:commons-lang:jar:2.1 (scope = compile)
[INFO]    dom4j:dom4j:jar:1.6.1 (scope = compile)
[INFO]    jaxen:jaxen:jar:1.1.1 (scope = compile)
[INFO]    jdom:jdom:jar:1.0 (scope = compile)
[INFO]    junit:junit:jar:3.8.1 (scope = test)
[INFO]    log4j:log4j:jar:1.2.14 (scope = compile)
[INFO]    oro:oro:jar:2.0.8 (scope = compile)
[INFO]    velocity:velocity:jar:1.5 (scope = compile)
[INFO]    xalan:xalan:jar:2.6.0 (scope = compile)
[INFO]    xerces:xercesImpl:jar:2.6.2 (scope = compile)
[INFO]    xerces:xmlParserAPIs:jar:2.6.2 (scope = compile)
[INFO]    xml-apis:xml-apis:jar:1.0.b2 (scope = compile)
[INFO]    xom:xom:jar:1.0 (scope = compile)

As you can see, our project has a very large set of dependencies. Although we included direct dependencies on only 4 libraries, we appear to be depending on 15 dependencies in total. Dom4J depends on Xerces and the XML Parser APIs, whereas Jaxen depends on Xalan being available in the classpath. The Dependency plugin will print out the final combination of dependencies under which your project is being compiled. If you would like to know about the entire dependency tree of your project, you can run the dependency:tree goal.

$ mvn dependency:tree
...
[INFO] [dependency:tree]
[INFO] org.sonatype.mavenbook.ch04:simple-weather:jar:1.0
[INFO] +- log4j:log4j:jar:1.2.14:compile
[INFO] +- dom4j:dom4j:jar:1.6.1:compile
[INFO] |  \- xml-apis:xml-apis:jar:1.0.b2:compile
[INFO] +- jaxen:jaxen:jar:1.1.1:compile
[INFO] |  +- jdom:jdom:jar:1.0:compile
[INFO] |  +- xerces:xercesImpl:jar:2.6.2:compile
[INFO] |  \- xom:xom:jar:1.0:compile
[INFO] |     +- xerces:xmlParserAPIs:jar:2.6.2:compile
[INFO] |     +- xalan:xalan:jar:2.6.0:compile
[INFO] |     \- com.ibm.icu:icu4j:jar:2.6.1:compile
[INFO] +- velocity:velocity:jar:1.5:compile
[INFO] |  +- commons-collections:commons-collections:jar:3.1:compile
[INFO] |  +- commons-lang:commons-lang:jar:2.1:compile
[INFO] |  \- oro:oro:jar:2.0.8:compile
[INFO] +- org.apache.commons:commons-io:jar:1.3.2:test
[INFO] \- junit:junit:jar:3.8.1:test
...

If you’re truly adventurous or want to see the full dependency trail, including artifacts that were rejected due to conflicts and other reasons, run Maven with the debug flag:

$ mvn install -X
...
[DEBUG] org.sonatype.mavenbook.ch04:simple-weather:jar:1.0 (selected for null)
[DEBUG]   log4j:log4j:jar:1.2.14:compile (selected for compile)
[DEBUG]   dom4j:dom4j:jar:1.6.1:compile (selected for compile)
[DEBUG]     xml-apis:xml-apis:jar:1.0.b2:compile (selected for compile)
[DEBUG]   jaxen:jaxen:jar:1.1.1:compile (selected for compile)
[DEBUG]     jaxen:jaxen:jar:1.1-beta-6:compile (removed - causes a cycle 
    in the graph)
[DEBUG]     jaxen:jaxen:jar:1.0-FCS:compile (removed - causes a cycle in 
    the graph)
[DEBUG]     jdom:jdom:jar:1.0:compile (selected for compile)
[DEBUG]     xml-apis:xml-apis:jar:1.3.02:compile (removed - nearer found: 
    1.0.b2)
[DEBUG]     xerces:xercesImpl:jar:2.6.2:compile (selected for compile)
[DEBUG]     xom:xom:jar:1.0:compile (selected for compile)
[DEBUG]       xerces:xmlParserAPIs:jar:2.6.2:compile (selected for compile)
[DEBUG]       xalan:xalan:jar:2.6.0:compile (selected for compile)
[DEBUG]       xml-apis:xml-apis:1.0.b2.
[DEBUG]       com.ibm.icu:icu4j:jar:2.6.1:compile (selected for compile)
[DEBUG]   velocity:velocity:jar:1.5:compile (selected for compile)
[DEBUG]     commons-collections:commons-collections:jar:3.1:compile 
    (selected for compile)
[DEBUG]     commons-lang:commons-lang:jar:2.1:compile (selected for compile)
[DEBUG]     oro:oro:jar:2.0.8:compile (selected for compile)
[DEBUG]   junit:junit:jar:3.8.1:test (selected for test)
...

In the debug output, we see some of the guts of the dependency management system at work. What you see here is the tree of dependencies for this project. Maven is printing out the full Maven coordinates for all of your project’s dependencies and the dependencies of your dependencies (and the dependencies of your dependencies’ dependencies). You can see that simple-weather depends on jaxen, which depends on xom, which in turn depends on icu4j. You can also see that Maven is creating a graph of dependencies, eliminating duplicates, and resolving any conflicts between different versions. If you are having problems with dependencies, it is often helpful to dig a little deeper than the list generated by dependency:resolve. Turning on the debug output allows you to see Maven’s dependency mechanism at work.

Writing Unit Tests

Maven has built-in support for unit tests, and testing is a part of the default Maven lifecycle. Let’s add some unit tests to our simple weather project. First, let’s create the org.sonatype.mavenbook.weather package under src/test/java:

$ cd src/test/java
$ cd org/sonatype/mavenbook
$ mkdir weather
$ cd weather

At this point, we will create two unit tests. The first will test the YahooParser, and the second will test the WeatherFormatter. In the weather package, create a file named YahooParserTest.java with the contents shown in Example 4-11.

Example 4-11. simple-weather’s YahooParserTest unit test
package org.sonatype.mavenbook.weather.yahoo;

import java.io.InputStream;

import junit.framework.TestCase;

import org.sonatype.mavenbook.weather.Weather;
import org.sonatype.mavenbook.weather.YahooParser;

public class YahooParserTest extends TestCase {

  public YahooParserTest(String name) {
    super(name);
  }
 
  public void testParser() throws Exception {
    InputStream nyData = 
      getClass().getClassLoader().getResourceAsStream("ny-weather.xml");
    Weather weather = new YahooParser().parse( nyData );
    assertEquals( "New York", weather.getCity() );
    assertEquals( "NY", weather.getRegion() );
    assertEquals( "US", weather.getCountry() );
    assertEquals( "39", weather.getTemp() );
    assertEquals( "Fair", weather.getCondition() );
    assertEquals( "39", weather.getChill() );
    assertEquals( "67", weather.getHumidity() );
  }
}

This YahooParserTest extends the TestCase class defined by JUnit. It follows the usual pattern for a JUnit test: a constructor that takes a single String argument that calls the constructor of the superclass, and a series of public methods that begin with “test” that are invoked as unit tests. We define a single test method, testParser, which tests the YahooParser by parsing an XML document with known values. The test XML document is named ny-weather.xml and is loaded from the classpath. We’ll add test resources in Adding Unit Test Resources.” In our Maven project’s directory layout, the ny-weather.xml file is found in the directory that contains test resources—${basedir}/src/test/resources under org/sonatype/mavenbook/weather/yahoo/ny-weather.xml. The file is read as an InputStream and passed to the parse() method on YahooParser. The parse() method returns a Weather object, which is then tested with a series of calls to assetEquals(), a method defined by TestCase.

In the same directory, create a file named WeatherFormatterTest.java. See Example 4-12.

Example 4-12. simple-weather’s WeatherFormatterTest unit test
package org.sonatype.mavenbook.weather.yahoo;

import java.io.InputStream;

import org.apache.commons.io.IOUtils;

import org.sonatype.mavenbook.weather.Weather;
import org.sonatype.mavenbook.weather.WeatherFormatter;
import org.sonatype.mavenbook.weather.YahooParser;

import junit.framework.TestCase;

public class WeatherFormatterTest extends TestCase {

  public WeatherFormatterTest(String name) {
    super(name);
  }

  public void testFormat() throws Exception {
    InputStream nyData = 
      getClass().getClassLoader().getResourceAsStream("ny-weather.xml");
    Weather weather = new YahooParser().parse( nyData );
    String formattedResult = new WeatherFormatter().format( weather );
    InputStream expected = 
      getClass().getClassLoader().getResourceAsStream("format-expected.dat");
    assertEquals( IOUtils.toString( expected ).trim(), 
                  formattedResult.trim() );
  }
}

The second unit test in this simple project tests the WeatherFormatter. Like the YahooParserTest, the WeatherFormatterTest also extends JUnit’s TestCase class. The single test function reads the same test resource from ${basedir}/src/test/resources under the org/sonatype/mavenbook/weather/yahoo directory via this unit test’s classpath. We’ll add test resources in the section Adding Unit Test Resources,” later in this chapter. WeatherFormatterTest runs this sample input file through the YahooParser, which spits out a Weather object, and this object is then formatted with the WeatherFormatter. Since the WeatherFormatter prints out a String, we need to test it against some expected input. Our expected input has been captured in a text file named format-expected.dat, which is in the same directory as ny-weather.xml. To compare the test’s output to the expected output, we read this expected output in as an InputStream and use Apache Commons IO’s IOUtils class to convert this file to a String. This String is then compared to the test output using assertEquals().

Adding Test-Scoped Dependencies

In WeatherFormatterTest, we used a utility from Apache Commons IO—the IOUtils class. IOUtils provides a number of helpful static functions that take most of the work out of input/output operations. In this particular unit test, we used IOUtils.toString() to copy the format-expected.dat classpath resource to a String. We could have done this without using Commons IO, but it would have required an extra six or seven lines of code to deal with the various InputStreamReader and StringWriter objects. The main reason we used Commons IO was to give us an excuse to add a test-scoped dependency on Commons IO.

A test-scoped dependency is a dependency that is available on the classpath only during test compilation and test execution. If your project has war or ear packaging, a test-scoped dependency would not be included in the project’s output archive. To add a test-scoped dependency, add the dependency element to your project’s dependencies section, as shown in Example 4-13.

Example 4-13. Adding a test-scoped dependency
<project>
  ...
  <dependencies>
    ...
    <dependency>
      <groupId>org.apache.commons</groupId>
      <artifactId>commons-io</artifactId>
      <version>1.3.2</version>
      <scope>test</scope>
    </dependency>
    ...
  </dependencies>
</project>

After you add this dependency to the pom.xml, run mvn dependency:resolve and you should see that commons-io is now listed as a dependency with scope test. We need to do one more thing before we are ready to run this project’s unit tests: create the classpath resources these unit tests depend on. Dependency scopes are explained in detail in Dependency Scope” in Chapter 8.

Adding Unit Test Resources

A unit test has access to a set of resources that are specific to tests. Often, you’ll store files containing expected results and files containing dummy input in the test classpath. In this project, we’re storing a test XML document for YahooParserTest named ny-weather.xml and a file containing expected output from the WeatherFormatter in format-expected.dat.

To add test resources, you’ll need to create the src/test/resources directory. This is the default directory in which Maven looks for unit test resources. To create this directory, execute the following commands from your project’s base directory:

$ cd src/test
$ mkdir resources
$ cd resources

Once you’ve created the resources/ directory, create a file named format-expected.dat there. See Example 4-14.

Example 4-14. simple-weather’s WeatherFormatterTest expected output
*********************************
 Current Weather Conditions for:
  New York, NY, US
  
 Temperature: 39
   Condition: Fair
    Humidity: 67
  Wind Chill: 39
*********************************

This file should look familiar. It is the same output that was generated previously when you ran the simple weather project with the Maven Exec plugin. The second file you’ll need to add to the resources directory is ny-weather.xml. See Example 4-15.

Example 4-15. simple-weather’s YahooParserTest XML input
<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
<rss version="2.0" xmlns:yweather="http://xml.weather.yahoo.com/ns/rss/1.0" 
     xmlns:geo="http://www.w3.org/2003/01/geo/wgs84_pos#">
 <channel>
 <title>Yahoo! Weather - New York, NY</title>
 <link>http://us.rd.yahoo.com/dailynews/rss/weather/New_York__NY/</link>
 <description>Yahoo! Weather for New York, NY</description>
 <language>en-us</language>
 <lastBuildDate>Sat, 10 Nov 2007 8:51 pm EDT</lastBuildDate>

 <ttl>60</ttl>
 <yweather:location city="New York" region="NY" country="US" />
 <yweather:units temperature="F" distance="mi" pressure="in" speed="mph" />
 <yweather:wind chill="39" direction="0" speed="0" />
 <yweather:atmosphere humidity="67" visibility="1609" pressure="30.18" 
                      rising="1" />
  <yweather:astronomy sunrise="6:36 am" sunset="4:43 pm" />
  <image>
 <title>Yahoo! Weather</title>

 <width>142</width>
 <height>18</height>
 <link>http://weather.yahoo.com/</link>
 <url>http://l.yimg.com/us.yimg.com/i/us/nws/th/main_142b.gif</url>
 </image>
 <item>
 <title>Conditions for New York, NY at 8:51 pm EDT</title>

  <geo:lat>40.67</geo:lat>
 <geo:long>-73.94</geo:long>
  <link>http://us.rd.yahoo.com/dailynews/rss/weather/New_York__NY/\</link>
 <pubDate>Sat, 10 Nov 2007 8:51 pm EDT</pubDate>
 <yweather:condition text="Fair" code="33" temp="39" 
                     date="Sat, 10 Nov 2007 8:51 pm EDT" />
 <description><![CDATA[
<img src="http://l.yimg.com/us.yimg.com/i/us/we/52/33.gif" /><br />
 <b>Current Conditions:</b><br />
 Fair, 39 F<BR /><BR />
 <b>Forecast:</b><BR />
  Sat - Partly Cloudy. High: 45 Low: 32<br />
  Sun - Sunny. High: 50 Low: 38<br />
 <br />
 ]]></description>
 <yweather:forecast day="Sat" date="10 Nov 2007" low="32" high="45" 
                    text="Partly Cloudy" code="29" />

<yweather:forecast day="Sun" date="11 Nov 2007" low="38" high="50" 
                   text="Sunny" code="32" />
  <guid isPermaLink="false">10002_2007_11_10_20_51_EDT</guid>
 </item>
</channel>
</rss>

This file contains a test XML document for the YahooParserTest. We store this file so that we can test the YahooParser without having to retrieve an XML response from Yahoo! Weather.

Executing Unit Tests

Now that your project has unit tests, let’s run them. You don’t have to do anything special to run a unit test; the test phase is a normal part of the Maven lifecycle. You run Maven tests whenever you run mvn package or mvn install. If you would like to run all the lifecycle phases up to and including the test phase, run mvn test:

$ mvn test
...
[INFO] [surefire:test]
[INFO] Surefire report directory: ~/examples/simple-weather/target/\
                                  surefire-reports

-------------------------------------------------------
 T E S T S
-------------------------------------------------------
Running org.sonatype.mavenbook.weather.yahoo.WeatherFormatterTest
0    INFO  YahooParser  - Creating XML Reader
177  INFO  YahooParser  - Parsing XML Response
239  INFO  WeatherFormatter  - Formatting Weather Data
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.547 sec
Running org.sonatype.mavenbook.weather.yahoo.YahooParserTest
475  INFO  YahooParser  - Creating XML Reader
483  INFO  YahooParser  - Parsing XML Response
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.018 sec

Results :

Tests run: 2, Failures: 0, Errors: 0, Skipped: 0

Executing mvn test from the command line causes Maven to execute all lifecycle phases up to the test phase. The Maven Surefire plugin has a test goal that is bound to the test phase. This test goal executes all of the unit tests that this project can find under src/test/java. In the case of this project, you can see that the Surefire plugin’s test goal executes WeatherFormatterTest and YahooParserTest. When the Surefire plugin runs the JUnit tests, it also generates XML and text reports in the ${basedir}/target/surefire-reports directory. If your tests are failing, you should look in this directory for details such as stack traces and error messages generated by your unit tests.

Ignoring Test Failures

You will often find yourself developing on a system that has failing unit tests. If you are practicing Test-Driven Development (TDD), you might use test failure as a measure of how close your project is to completeness. If you have failing unit tests, and you would still like to produce build output, you are going to have to tell Maven to ignore build failures. When Maven encounters a build failure, its default behavior is to stop the current build. To continue building a project even when the Surefire plugin encounters failed test cases, you’ll need to set the testFailureIgnore configuration property of the Surefire plugin to true. See Example 4-16.

Example 4-16. Ignoring unit test failures
<project>
  [...]
  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-surefire-plugin</artifactId>
        <configuration>
          <testFailureIgnore>true</testFailureIgnore>
        </configuration>
      </plugin>
    </plugins>
  </build>
  [...]
</project>

The plugin documents (http://maven.apache.org/plugins/maven-surefire-plugin/test-mojo.html) show that this parameter declares an expression, as shown in Example 4-17.

Example 4-17. Plugin parameter expressions
    testFailureIgnore  Set this to true to ignore a failure during \
                          testing. Its use is NOT RECOMMENDED, but quite \
                          convenient on occasion.

    * Type: boolean
    * Required: No
    * Expression: ${maven.test.failure.ignore}

This expression can be set from the command line using the -D parameter:

$ mvn test -Dmaven.test.failure.ignore=true

Skipping Unit Tests

You may want to configure Maven to skip unit tests altogether. Maybe you have a very large system where the unit tests take minutes to complete and you don’t want to wait for them before producing output. Or maybe you are working with a legacy system that has a series of failing unit tests, and instead of fixing them, you just want to produce a JAR. Maven allows you to skip unit tests using the skip parameter of the Surefire plugin. To skip tests from the command line, simply add the maven.test.skip property to any goal:

$ mvn install -Dmaven.test.skip=true
...
[INFO] [compiler:testCompile]
[INFO] Not compiling test sources
[INFO] [surefire:test]
[INFO] Tests are skipped.
...

When the Surefire plugin reaches the test goal, it will skip the unit tests if the maven.test.skip properties is set to true. Another way to configure Maven to skip unit tests is to add the configuration shown in Example 4-18 to your project’s pom.xml. To do this, you would add a plugin element to your build configuration.

Example 4-18. Skipping unit tests
<project>
  [...]
  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-surefire-plugin</artifactId>
        <configuration>
          <skip>true</skip>
        </configuration>
      </plugin>
    </plugins>
  </build>
  [...]
</project>

Building a Packaged Command-Line Application

In the Running the Simple Weather Program” section, earlier in this chapter, we executed our application using the Maven Exec plugin. Although that plugin executed the program and produced some output, you shouldn’t look to Maven as an execution container for your applications. If you are distributing this command-line application to others, you will probably want to distribute a JAR or an archive as a ZIP or TAR’d GZIP file. This section outlines a process for using a predefined assembly descriptor in the Maven Assembly plugin to produce a distributable JAR file, which contains the project’s bytecode and all of the dependencies.

You can use the Maven Assembly plugin to create arbitrary distributions for your applications. Use it to assemble the output of your project in any format you desire by defining a custom assembly descriptor. In a later chapter, we will show you how to create a custom assembly descriptor that produces a more complex archive for the simple weather application. In this chapter, we’re going to use the predefined jar-with-dependencies format. To configure the Assembly Plugin, we need to add the plugin configuration shown in Example 4-19 to our existing build configuration in the pom.xml.

Example 4-19. Configuring the Maven Assembly descriptor
<project>
  [...]
  <build>
    <plugins>
      <plugin>
        <artifactId>maven-assembly-plugin</artifactId>
        <configuration>
          <descriptorRefs>
            <descriptorRef>jar-with-dependencies</descriptorRef>
          </descriptorRefs>
        </configuration>
      </plugin>
    </plugins>
  </build>
  [...]
</project>

Once you’ve added this configuration, you can build the assembly by running mvn assembly:assembly, like so:

$ mvn install assembly:assembly
...
[INFO] [jar:jar]
[INFO] Building jar: ~/examples/simple-weather/target/simple-weather-1.0.jar
[INFO] [assembly:assembly]
[INFO] Processing DependencySet (output=)
[INFO] Expanding: \
       .m2/repository/dom4j/dom4j/1.6.1/dom4j-1.6.1.jar into \
       /tmp/archived-file-set.1437961776.tmp
[INFO] Expanding: .m2/repository/commons-lang/commons-lang/2.1/\
                     commons-lang-2.1.jar
       into /tmp/archived-file-set.305257225.tmp
... (Maven Expands all dependencies into a temporary directory) ...
[INFO] Building jar: \
       ~/examples/simple-weather/target/\
         simple-weather-1.0-jar-with-dependencies.jar

Once the assembly is assembled in target/simple-weather-1.0-jar-with-dependencies.jar, you can run the Main class again from the command line. To run the simple weather app’s Main class, execute the following from your project’s base directory:

$ cd target
$ java -cp simple-weather-1.0-jar-with-dependencies.jar \
                    org.sonatype.mavenbook.weather.Main 10002
0    INFO  YahooRetriever  - Retrieving Weather Data
221  INFO  YahooParser  - Creating XML Reader
399  INFO  YahooParser  - Parsing XML Response
474  INFO  WeatherFormatter  - Formatting Weather Data
*********************************
 Current Weather Conditions for:
  New York, NY, US
  
 Temperature: 44
   Condition: Fair
    Humidity: 40
  Wind Chill: 40
*********************************

The jar-with-dependencies format creates a single JAR file that includes all of the bytecode from the simple-weather project as well as the unpacked bytecode from all of the dependencies. This somewhat unconventional format produces a 9 MiB JAR file containing approximately 5,290 classes, but it does provide for an easy distribution format for applications you’ve developed with Maven. Later in this book, we’ll show you how to create a custom assembly descriptor to produce a more standard distribution.

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