what is java class loaer code example
Example 1: custom classloader
package test.main;
import java.io.DataInputStream;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
public class MyClassLoader extends ClassLoader {
public MyClassLoader(ClassLoader parent) {
super(parent);
}
@Override
public Class<?> loadClass(String name) throws ClassNotFoundException {
System.out.println("Class Loading Started for " + name);
if (name.startsWith("test")) {
return getClass(name);
}
return super.loadClass(name);
}
/**
* Loading of class from .class file
* happens here You Can modify logic of
* this method to load Class
* from Network or any other source
* @param name
* @return
* @throws ClassNotFoundException
*/
private Class<?> getClass(String name) throws ClassNotFoundException {
System.out.println("*********Inside getClass*********");
String file = name.replace('.', File.separatorChar) + ".class";
System.out.println("Name of File" + file);
byte[] byteArr = null;
try {
// This loads the byte code data from the file
byteArr = loadClassData(file);
System.out.println("Size of byte array "+byteArr.length);
Class<?> c = defineClass(name, byteArr, 0, byteArr.length);
resolveClass(c);
return c;
} catch (IOException e) {
e.printStackTrace();
return null;
}
}
/**
* Loads a given file and converts
* it into a Byte Array
* @param name
* @return
* @throws IOException
*/
private byte[] loadClassData(String name) throws IOException {
System.out.println("<<<<<<<<<Inside loadClassData>>>>>>");
InputStream stream = getClass().getClassLoader().getResourceAsStream(
name);
int size = stream.available();
byte buff[] = new byte[size];
DataInputStream in = new DataInputStream(stream);
// Reading the binary data
in.readFully(buff);
in.close();
return buff;
}
}
Example 2: custom classloader
package test.main;
import java.lang.reflect.InvocationTargetException;
public class Test {
public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException, NoSuchMethodException, Exception {
MyClassLoader loader = new MyClassLoader(
Test.class.getClassLoader());
System.out.println("loader name---- " +loader.getParent().getClass().getName());
//This Loads the Class we must always
//provide binary name of the class
Class<?> clazz =
loader.loadClass("test.frugalis.Frugalis");
System.out.println("Loaded class name: " + clazz.getName());
//Create instance Of the Class and invoke the particular method
Object instance = clazz.newInstance();
clazz.getMethod("printMyName").invoke(instance);
}
}