Apache Ant InputHandler

Apache Ant is a popular build tool used by developers to automate their software builds. One of the key features of Ant is its ability to accept input from users during the build process. This is where the InputHandler comes in.

The InputHandler is a component of Ant that allows developers to prompt users for input during the build process. This input can then be used by Ant's build scripts to make decisions or customize the build process for the user.

How It Works

The input handler is specified in the build script by setting the inputhandler attribute on the project element to the fully qualified class name of the input handler. When Ant needs to prompt the user for input, it creates an instance of the input handler and calls its handleInput method.

Here is an example of how to set the input handler in an Ant build file:

<project name="MyProject" default="build" basedir=".">
   <property name="my.input.handler" value="com.example.MyInputHandler"/>

   <target name="build">
      <input handler="${my.input.handler}" message="Enter a value:" addproperty="my.property"/>
      <echo message="The value entered was: ${my.property}" />
   </target>
</project>

In this example, the input task is used to prompt the user for a value. The handler attribute specifies the input handler to use (com.example.MyInputHandler), and the message attribute provides the prompt to display. The addproperty attribute sets the value of the my.property property to the value entered by the user.

Implementing an Input Handler

To implement an input handler, you need to create a class that extends the org.apache.tools.ant.input.InputHandler abstract class. This class must override the handleInput method, which is called by Ant to prompt the user for input.

Here is an example implementation of an input handler:

package com.example;

import org.apache.tools.ant.input.InputRequest;
import org.apache.tools.ant.input.InputHandler;

public class MyInputHandler extends InputHandler {
   @Override
   public void handleInput(InputRequest request) {
      String prompt = request.getPrompt();
      String defaultValue = request.getDefaultValue();
      String input = System.console().readLine("%s [%s]: ", prompt, defaultValue);
      if ((input == null || input.trim().isEmpty()) && defaultValue != null) {
         input = defaultValue;
      }
      request.setInput(input);
   }
}

This input handler prompts the user for input using the console, and uses any default value specified by the InputRequest. If the user enters a value, it is set as the value of the InputRequest using the setInput method.

Conclusion

The Apache Ant InputHandler is a powerful tool for allowing users to provide input during the build process. By setting the input handler in the build script, developers can prompt users for input and use it to customize the build process. Implementing a custom input handler is easy, and provides flexibility for developers to customize the user experience of their Ant build scripts.