简单了解 Java 类加载 | Jalen's Blog = Follow your heart = A happy life

	package com.example.demo.test1;

	import sun.misc.Launcher;

	import java.io.File;
	import java.util.StringTokenizer;

	/**
	* <p>
	* <code>TestClassLoader</code>
	* </p>
	* Description: java 类加载机制
	*
	* @author Chu Mingcheng
	* @date 2018/9/10
	*/
	public class TestClassLoader extends Launcher{

	public static void main(String[] args) {
	TestClassLoader test = new TestClassLoader();
	test.testAppClassLoader();
	test.testBootstrapLoader();
	test.test4();
	}

	/**
	* test AppClassLoader
	*/
	private void testAppClassLoader(){
	System.out.println("\n----------AppClassLoader：应用（系统）类加载器------------");
	final String s = System.getProperty("java.class.path");
	System.out.println(s);
	final File[] path = (s == null) ? new File[0] : getClassPath(s);
	for(File f : path){
	System.out.println(f);
	}
	}

	/**
	* test ExtClassLoader
	*/
	private void test4(){
	System.out.println("\n---------ExtClassLoader：扩展类加载器-------------");
	final String s = System.getProperty("java.ext.dirs");// 对应路径
	System.out.println(s);

	File[] dirs;
	if (s != null) {
	StringTokenizer st =
	new StringTokenizer(s, File.pathSeparator);
	int count = st.countTokens();
	dirs = new File[count];
	for (int i = 0; i < count; i++) {
	dirs[i] = new File(st.nextToken());
	}
	} else {
	dirs = new File[0];
	}

	for(File f:dirs){
	System.out.println(f.getAbsolutePath());
	}
	}

	/**
	* test BootClassLoader
	*/
	private void testBootstrapLoader(){
	System.out.println("\n--------BootstrapLoader：启动类（根）加载器--------------");
	final String s = System.getProperty("sun.boot.class.path");
	System.out.println(s);
	final File[] path = (s == null) ? new File[0] : getClassPath(s);
	for(File f : path){
	System.out.println(f);
	}
	//sun.misc.Launcher launcher = sun.misc.Launcher.getLauncher();
	//System.out.println(launcher.getClass().getClassLoader());
	}

	/**
	* Launcher 类私有方法，这里是直接复制一份过来的
	* @see sun.misc.Launcher#getClassPath
	* @param var0
	* @return
	*/
	private static File[] getClassPath(String var0) {
	File[] var1;
	if (var0 != null) {
	int var2 = 0;
	int var3 = 1;
	boolean var4 = false;

	int var5;
	int var7;
	for(var5 = 0; (var7 = var0.indexOf(File.pathSeparator, var5)) != -1; var5 = var7 + 1) {
	++var3;
	}

	var1 = new File[var3];
	var4 = false;

	for(var5 = 0; (var7 = var0.indexOf(File.pathSeparator, var5)) != -1; var5 = var7 + 1) {
	if (var7 - var5 > 0) {
	var1[var2++] = new File(var0.substring(var5, var7));
	} else {
	var1[var2++] = new File(".");
	}
	}

	if (var5 < var0.length()) {
	var1[var2++] = new File(var0.substring(var5));
	} else {
	var1[var2++] = new File(".");
	}

	if (var2 != var3) {
	File[] var6 = new File[var2];
	System.arraycopy(var1, 0, var6, 0, var2);
	var1 = var6;
	}
	} else {
	var1 = new File[0];
	}

	return var1;
	}
	}