Mega Code Archive
Jar info class loader
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package com.ack.tools.jarinfo;
import java.net.MalformedURLException;
import java.net.URL;
import java.security.SecureClassLoader;
/**
* This extension to a the SecureClassLoader is responsible for
* loading classes from the supplied zip/jar file. These classes
* will be loaded if they cannot be found using the parent
* class loader.
*
* @see java.security.SecureClassLoader
*/
public class JarInfoClassLoader extends SecureClassLoader {
private JarClassByteCache fClassTable;
private String fJarURLPath;
/**
* Create a class loader that will read the files
* from the supplied zip/jar file
* @param the zip/jar file to check for loaded classes
* @exception is thrown if any errors occur during the
* reading of the jar/zip file
*/
public JarInfoClassLoader( String zipFile ) throws JarInfoException {
this( zipFile, ClassLoader.getSystemClassLoader() );
}
/**
* Create a class loader that will read the files
* from the supplied zip/jar file
* @param the zip/jar file to check for loaded classes
* @param the parent class loader for this class
* @exception is thrown if any errors occur during the
* reading of the jar/zip file
*/
public JarInfoClassLoader( String zipFile, ClassLoader cl ) throws JarInfoException {
super( cl );
fClassTable = new JarClassByteCache( zipFile );
}
/**
* accessor method to get hold of the byte cache
*
* @return the jar byte cache of classes
*/
public JarClassByteCache getClassCache() {
return fClassTable;
}
/**
* Under Java 2 this method is called to find a class.
* It is based on new delegation model for loading classes,
* and will be called by the loadClass method after checking
* the parent class loader for the requested class. The parent
* class loader is supplied by the constructors of this class.
*/
public Class findClass( String className ) throws ClassNotFoundException {
// get the bytes for a classes from the class table
byte[] b = null;
try {
b = fClassTable.getClassBytes( className );
}
catch( JarInfoException jie ) {
}
// and if there are some, use the inherited method defineClass
// to convert a these bytes into an instance of a Class
if( b != null ) {
return defineClass( className, b, 0, b.length );
}
// otherwise if there is not such class
return null;
}
/**
* check to see if the supplied resource is in the jar. This method
* is call if all other attempts by the Java Runtime to find this
* resource failed.
*
*@param the name of the resource
*@return the URL for the resource
*@see java.lang.ClassLoader#findResource
*/
protected URL findResource( String resource ) {
if( fClassTable.getJarInfo().hasResource( resource ) ) {
try {
return new URL( getJarURL() + resource );
}
catch( MalformedURLException mue ) {
}
}
return null;
}
/**
*@return the URL for the supplied jar
*/
private String getJarURL() {
if( fJarURLPath == null ) {
StringBuffer buf = new StringBuffer( "jar:file:" );
String jarFile = fClassTable.getJarInfo().zipFileName();
buf.append( jarFile.replace( '\\', '/' ) );
buf.append( "!/" );
fJarURLPath = buf.toString();
}
return fJarURLPath;
}
}
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