Monday, January 19, 2009

Using Ant as a library

Ant has a lot of predefined tasks that could be a great help. You can use them directly from your Java code. Here are some examples using Ant to download a file, unzip a package and exec some shell command.

You would need to have
+ ant-1.7.1.jar
+ ant-launcher-1.7.1.jar
+ commons-io-1.3.2.jar (for exec example, found at http://commons.apache.org/io)

in your classpath.


public class AntDemo {

/**
* Download a file at sourceUrl to dest
*
*/
public static void download(URL sourceUrl, File dest) {
Project dummyProject = new Project();
dummyProject.init();

Get antGet = new Get();
antGet.setProject(dummyProject);
antGet.setVerbose(true);
antGet.setSrc(sourceUrl);
antGet.setDest(dest);
antGet.execute();
}

/**
* Unzip a zip file
*
*/
public static void unzip(File src, File dest) {
Project dummyProject = new Project();
dummyProject.init();

Expand antUnzip = new Expand();
antUnzip.setProject(dummyProject);
antUnzip.setSrc(src);
antUnzip.setDest(dest);
antUnzip.execute();

/* ant doesn't preserve permission bits
need to restore them manually */

Chmod chmod = new Chmod();
chmod.setProject(dummyProject);
chmod.setDir(new File(src.getAbsolutePath().replaceAll(".zip", "")));
chmod.setPerm("a+rx");
chmod.setIncludes("**/**");
chmod.execute();
}


/**
* Run a shell command and return the output as String
*
*/
public static String exec(String command, List params, File workDir) {
File outputFile;
try {
outputFile = File.createTempFile("exec", ".out");
} catch (IOException e) {
throw new RuntimeException(e);
}

Project dummyProject = new Project();
dummyProject.init();

ExecTask execTask = new ExecTask();
execTask.setProject(dummyProject);
execTask.setOutput(outputFile);
execTask.setDir(workDir != null ? workDir : new File(System
.getProperty("user.dir")));
execTask.setExecutable(command);
if (params != null) {
for (String param : params) {
execTask.createArg().setValue(param);
}
}

execTask.execute();

FileReader reader = null;
try {
reader = new FileReader(outputFile);
return IOUtils.toString(reader);
} catch (Exception e) {
throw new RuntimeException(e);
} finally {
IOUtils.closeQuietly(reader);
outputFile.delete();
}
}

public static void main(String[] args) {
List params = Arrays.asList(new String[] { "Hello", "World" });
System.out.println(exec("echo", params, null));
}
}


Just note that you'll need a dummy project for the Ant task. Otherwise you'll get an NullPointerException.

There are a lot of tasks that you could use. The list is here http://ant.apache.org/manual/tasksoverview.html
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