Building Java Applications for the iSeries Server with VisualAge for Java 3.5

Chapter 10. Structured Query Language for Java (SQLJ) 407

Consider these points when you compare SQLJ and JDBC:

򐂰 SQLJ source programs are smaller than the equivalent JDBC programs.

򐂰 SQLJ programs allow direct embedding of Java bind expressions within SQL statements.

JDBC requires a separate call statement for each bind variable and specifies the binding

by position number.

򐂰 SQLJ provides strong type checking of query output and returns parameters on

pre-compile. JDBC passes values to and from SQL without compile-time type checking.

򐂰 SQLJ provides simplified rules for SQL statements and for calling stored procedures and

functions. JDBC requires more statements and takes more time and effort to code.

򐂰 SQLJ generates JDBC statements. You do not have complete control of the JDBC

statements as you do when writing it directly.

򐂰 If performance is your major concern, consider using JDBC rather than SQLJ because you

can deal directly with the JDBC statements.

10.2.1 An overview of how SQLJ works

This is an overview of how to program using SQLJ and Java. The SQL statement is written in

the Java source within curly brackets ({}) and it is preceded by a symbol #sql, for example:

#sql { select CFIRST into :customerName from CSTMR where CID = :cstno }

This is all you need to enter to retrieve a customer record from the CSTMR file. This is much

simpler than JDBC and is a more natural way of coding SQL statements.

To use SQLJ, the member type of the Java source is different and needs to be converted into

Java code using a translator. This translator converts the SQL statement into JDBC

statements. For example, we have the following .sqlj source file:

HelloWorld.sqlj

This member type needs to be translated by the SQLJ translator, for example:

Sqlj HelloWorld.sqlj

As a result of running the translator, the following files are generated:

򐂰 HelloWorld.java

򐂰 HelloWorld.class

򐂰 HelloWorld_SJProfileKeys.class

򐂰 HelloWorld_SJProfile0.ser

The Java source and class files are standard Java files. The translator generates the

additional class and .ser file to handle the conversion of the SQL statements to JDBC

statements.

VisualAge for Java also provides an SQLJ tool that implements the SQLJ standard. The

translator component is integrated into the IDE, so you can import, translate, and edit SQLJ

files. The runtime environment is an installable feature that is added to your workspace. The

original .sqlj source files are maintained in your project resources directory, as are the

profiles.

In our examples, we use VisualAge for Java as a tool to store source files, translate source

files, and act as a runtime environment.