1.7 手写模拟Tomcat类加载器实现多版本代码共存隔离

1). 模拟实现Tomcat的webappClassLoader加载自己war包应用内不同版本类实现相互共存与隔离

package com.tuling.jvm;
import java.io.FileInputStream;
import java.lang.reflect.Method;
public class MyClassLoaderTest {
    static class MyClassLoader extends ClassLoader {
        private String classPath;
        public MyClassLoader(String classPath) {
            this.classPath = classPath;
        }
        private byte[] loadByte(String name) throws Exception {
            name = name.replaceAll("\\.", "/");
            FileInputStream fis = new FileInputStream(classPath + "/" + name
                    + ".class");
            int len = fis.available();
            byte[] data = new byte[len];
            fis.read(data);
            fis.close();
            return data;
        }
        protected Class<?> findClass(String name) throws ClassNotFoundException {
            try {
                byte[] data = loadByte(name);
                return defineClass(name, data, 0, data.length);
            } catch (Exception e) {
                e.printStackTrace();
                throw new ClassNotFoundException();
            }
        }
        /**
         * 重写类加载方法，实现自己的加载逻辑，不委派给双亲加载
         */
        protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException {
            synchronized (getClassLoadingLock(name)) {
                // First, check if the class has already been loaded
                Class<?> c = findLoadedClass(name);
                if (c == null) {
                    // If still not found, then invoke findClass in order
                    // to find the class.
                    long t1 = System.nanoTime();
                    //非自定义的类还是走双亲委派加载
                    if (!name.startsWith("com.tuling.jvm")) {
                        c = this.getParent().loadClass(name);
                    } else {
                        c = findClass(name);
                    }
                    // this is the defining class loader; record the stats
                    sun.misc.PerfCounter.getFindClassTime().addElapsedTimeFrom(t1);
                    sun.misc.PerfCounter.getFindClasses().increment();
                }
                if (resolve) {
                    resolveClass(c);
                }
                return c;
            }
        }
    }
    public static void main(String args[]) throws Exception {
        MyClassLoader classLoader = new MyClassLoader("D:/test");
        Class clazz = classLoader.loadClass("com.tuling.jvm.User");
        Object obj = clazz.newInstance();
        Method method = clazz.getDeclaredMethod("sout", null);
        method.invoke(obj, null);
        System.out.println(clazz.getClassLoader());
        System.out.println();
        MyClassLoader classLoader1 = new MyClassLoader("D:/test1");
        Class clazz1 = classLoader1.loadClass("com.tuling.jvm.User");
        Object obj1 = clazz1.newInstance();
        Method method1 = clazz1.getDeclaredMethod("sout", null);
        method1.invoke(obj1, null);
        System.out.println(clazz1.getClassLoader());
    }
}

2).User类，往D:/test和D:/test1中分别放两个包名一样、类名一样的类User，只sout函数的打印信息不一样。

package com.tuling.jvm;
public class User {
    private int id;
    private String name;
    public User() {
    }
    public User(int id, String name) {
        super();
        this.id = id;
        this.name = name;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public void sout() {
        System.out.println("=======自己的加载器加载类调用方法=======");
    }
}

3).结果