Jakarta Commons Cookbook

1.18. Validation of Method Parameters

Problem

You need to validate parameters passed to a method. You would prefer one line of code to test that a method parameter is valid.

Solution

Use Validate to check method parameters. Validate can check for empty or null parameters, as well as evaluate any logical conditions. Example 1-18 demonstrates the use of Validate to perform a few simple validations.

Example 1-18. Using Validate to perform simple validations

import org.apache.commons.lang.Validate;

public doSomething( int param1, Object[] param2, Collection param3 ) {

    Validate.isTrue( param1 > 0, "param must be greater than zero" );
    Validate.notEmpty( param2, "param2 must not be empty" );
    Validate.notEmpty( param3, "param3 must not be empty" );
    Validate.noNullElements( param3, "param3 cannot contain null elements" );

    // do something complex and interesting
}

Discussion

Write finicky methods. Don’t just work with any input, have some standards. Don’t hang around with garbage or nulls—clean up your act, and use Validate. Methods in Validate throw an IllegalArgumentException if invalid parameters are encountered. Validate.notEmpty( ) will throw an exception if the parameter is null or empty, and Validate.isTrue( ) takes a logical expression that must evaluate to true. Table 1-5 lists a number of static methods of Validate.

Table 1-5. Available static methods on Validate

Validate method	Description
isTrue(boolean expr)	Fails if expression evaluates to false
isTrue(boolean expr, String ...