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Extract children jar files inside of a jar file (which is often a self-contained executable jar file)
import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.;
import java.i FileOutputStream o.IOException;
import java.util.Enumeration;
import java.util.jar.JarFile;
import java.util.zip.ZipEntry;
/**
* This class extracts child jar files from a parent jar file. For example, if
* the parent jar `a.jar' contains a child jar `b.jar' under the
* <code>lib</code> directory, as shown below.
*
* <pre>
* <<< the structure of a.jar >>>
* a.jar (parent)
* L MANIFEST.MF
* L a.class
* L lib
* L b.jar (child)
* L MANIFEST.MF
* L b.class
* </pre>
*
* Then, you can only see `a.jar' since the other files are contained in it.
*
* <pre>
* <<< directory tree before extraction >>>
* ./ (base dir)
* L a.jar (parent)
* </pre>
*
* This class extracts `b.jar' with its parent directory.
*
* <pre>
* <<< after extraction >>>
* ./ (base dir)
* L a.jar (parent)
* L extracted (the directory where child files being extracted)
* L lib
* L b.jar
* </pre>
* @author Yuji Kosuga
*/
class JarExtractor {
/**
* @param args
* the first arg should be the path to the parent jar file, and
* the second should be the directory where child jar files are
* extracted.
*/
public static void main(String[] args) {
// JarExtractor ex = new JarExtractor(args[0], args[1]);
// For this demo, args are prefixed.
JarExtractor ex = new JarExtractor("a.jar", "extracted");
ex.parseJarFile();
}
private String parentPath = null;
private String extractPath = ".";
/**
* @param parentPath
* the path to the parent jar file
* @param extractPath
* the path to the directory where child files being extracted
*/
JarExtractor(String parentPath, String extractPath) {
this.parentPath = parentPath;
this.extractPath = extractPath;
}
/**
* @param parentJar
* the parent jar file
* @param extractee
* the file to be extracted
* @return the extracted jar file
* @throws IOException
*/
private File extractJarFileFromJar(final JarFile parentJar,
final ZipEntry extractee) throws IOException {
BufferedInputStream is = new BufferedInputStream(parentJar
.getInputStream(extractee));
File f = new File(extractPath + File.separator + extractee.getName());
String parentName = f.getParent();
if (parentName != null) {
File dir = new File(parentName);
dir.mkdirs();
}
BufferedOutputStream os = new BufferedOutputStream(
new FileOutputStream(f));
int c;
while ((c = is.read()) != -1) {
os.write((byte) c);
}
is.close();
os.close();
return f;
}
/**
* the default parseJarFile method
*/
private void parseJarFile() {
parseJarFile(new File(parentPath));
}
/**
* Parses the jar file.
* @param file
* the file to be parsed, which should be jar file, otherwise, an
* ioexception will be thrown.
*/
private void parseJarFile(final File file) {
if (file == null) {
throw new RuntimeException("file is null.");
}
JarFile jarFile = null;
try {
jarFile = new JarFile(file);
Enumeration entries = jarFile.entries();
while (entries.hasMoreElements()) {
ZipEntry entry = (ZipEntry) entries.nextElement();
if (entry.isDirectory()) {
continue;
}
String entryName = entry.toString();
if (entryName == null) {
continue;
} else if (entryName.endsWith(".jar")) {
// Found a child jar file inside the parent.
File f = extractJarFileFromJar(jarFile, entry);
if (f != null) {
// Try to extract descendant jar files from the child
// jar recursively.
parseJarFile(f);
}
}
}
} catch (Exception e) {
e.printStackTrace();
} finally {
if (jarFile != null) {
try {
jarFile.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
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