代理模式简介：https://www.jianshu.com/p/8ca38fc27485
几种代理模式
主要看jdk代理，大部分都会默认使用jdk的代理
jdk代理
先看jdk代理的类图
1.有上层接口
2.实现类(被代理类)
3.代理类(持有上层接口引用，通过Proxy重组字节码返回新的类，实现invocationHandler接口)
4.测试类(使用者：调用代理类实现被代理类的功能)
image.png
demo
上层接口
public interface IPerson {
void findLove();
void buyInsure();
}
实现类(被代理类)
public class Zhangsan implements IPerson {
public void findLove() {
System.out.println("张三要求：肤白貌美大长腿");
}
public void buyInsure() {
System.out.println("30万");
}
}
代理类
public class JdkMeipo implements InvocationHandler {
private IPerson target;
public IPerson getInstance(IPerson target){
this.target = target;
Class<?> clazz = target.getClass();
return (IPerson) Proxy.newProxyInstance(clazz.getClassLoader(),clazz.getInterfaces(),this);
}
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
before();
Object result = method.invoke(this.target,args);
after();
return result;
}
private void after() {
System.out.println("双方同意，开始交往");
}
private void before() {
System.out.println("我是媒婆，已经收集到你的需求，开始物色");
}
}
测试类
public class Test {
public static void main(String[] args) {
JdkMeipo jdkMeipo = new JdkMeipo();
IPerson zhangsan = jdkMeipo.getInstance(new Zhangsan());
zhangsan.findLove();
}
}
proxy
jdk代理关键在于通过proxy重组字节码
public static Object newProxyInstance(ClassLoader loader,
Class<?>[] interfaces,
InvocationHandler h)
三个参数
1.classloader用于找到目标类
2.interfaces找到目标类实现接口，进一步拿到方法
3.invocationHandler反射调用执行invoke方法
实现proxy.newProxyInstance
重组字节码->输出磁盘->编译成class->jvm加载->返回新对象
import javax.tools.JavaCompiler;
import javax.tools.StandardJavaFileManager;
import javax.tools.ToolProvider;
import java.io.File;
import java.io.FileWriter;
import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import java.lang.reflect.Parameter;
import java.util.HashMap;
import java.util.Map;
/**
* 用来生成源代码的工具类
*/
public class GPProxy {
public static final String ln = "\r\n";
public static Object newProxyInstance(GPClassLoader classLoader, Class<?> [] interfaces, GPInvocationHandler h){
try {
//1、动态生成源代码.java文件
String src = generateSrc(interfaces);
//2、Java文件输出磁盘
String filePath = GPProxy.class.getResource("").getPath();
File f = new File(filePath + "$Proxy0.java");
FileWriter fw = new FileWriter(f);
fw.write(src);
fw.flush();
fw.close();
//3、把生成的.java文件编译成.class文件
JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
StandardJavaFileManager manage = compiler.getStandardFileManager(null,null,null);
Iterable iterable = manage.getJavaFileObjects(f);
JavaCompiler.CompilationTask task = compiler.getTask(null,manage,null,null,null,iterable);
task.call();
manage.close();
//4、编译生成的.class文件加载到JVM中来
Class proxyClass = classLoader.findClass("$Proxy0");
Constructor c = proxyClass.getConstructor(GPInvocationHandler.class);
f.delete();
//5、返回字节码重组以后的新的代理对象
return c.newInstance(h);
}catch (Exception e){
e.printStackTrace();
}
return null;
}
private static String generateSrc(Class<?>[] interfaces){
StringBuffer sb = new StringBuffer();
sb.append(GPProxy.class.getPackage() + ";" + ln);
sb.append("import " + interfaces[0].getName() + ";" + ln);
sb.append("import java.lang.reflect.*;" + ln);
sb.append("public class $Proxy0 implements " + interfaces[0].getName() + "{" + ln);
sb.append("GPInvocationHandler h;" + ln);
sb.append("public $Proxy0(GPInvocationHandler h) { " + ln);
sb.append("this.h = h;");
sb.append("}" + ln);
for (Method m : interfaces[0].getMethods()){
Class<?>[] params = m.getParameterTypes();
StringBuffer paramNames = new StringBuffer();
StringBuffer paramValues = new StringBuffer();
StringBuffer paramClasses = new StringBuffer();
for (int i = 0; i < params.length; i++) {
Class clazz = params[i];
String type = clazz.getName();
String paramName = (clazz.getSimpleName()).toLowerCase();
if(i > 0 && i < params.length){
paramNames.append(",");
paramClasses.append(",");
paramValues.append(",");
}
paramNames.append(type + " " + paramName);
paramValues.append(paramName);
paramClasses.append(clazz.getName() + ".class");
}
sb.append("public " + m.getReturnType().getName() + " " + m.getName() + "(" + paramNames.toString() + ") {" + ln);
sb.append("try{" + ln);
sb.append("Method m = " + interfaces[0].getName() + ".class.getMethod(\"" + m.getName() + "\",new Class[]{" + paramClasses.toString() + "});" + ln);
sb.append(hasReturnValue(m.getReturnType()) ? "return " : "");
sb.append(m.getReturnType().getName().equals("void")?"":"("+m.getReturnType().getName()+")");
sb.append(getCaseCode("this.h.invoke(this,m,new Object[]{" + paramValues + "})",m.getReturnType()) + ";" + ln);
sb.append("}catch(Error _ex) { }");
sb.append("catch(Throwable e){" + ln);
sb.append("throw new UndeclaredThrowableException(e);" + ln);
sb.append("}");
sb.append(getReturnEmptyCode(m.getReturnType()));
sb.append("}");
}
sb.append("}" + ln);
return sb.toString();
}
private static Map<Class,Class> mappings = new HashMap<Class, Class>();
static {
mappings.put(int.class,Integer.class);
}
private static String getReturnEmptyCode(Class<?> returnClass){
if(mappings.containsKey(returnClass)){
return "return 0;";
}else if(returnClass == void.class){
return "";
}else {
return "return null;";
}
}
private static String getCaseCode(String code,Class<?> returnClass){
if(mappings.containsKey(returnClass)){
return "((" + mappings.get(returnClass).getName() + ")" + code + ")." + returnClass.getSimpleName() + "Value()";
}
return code;
}
private static boolean hasReturnValue(Class<?> clazz){
return clazz != void.class;
}
private static String toLowerFirstCase(String src){
char [] chars = src.toCharArray();
chars[0] += 32;
return String.valueOf(chars);
}
}
cglib代理
上类图
image.png
demo
被代理类
public class Customer {
public void findLove(){
System.out.println("要求：肤白貌美大长腿");
}
}
代理类
public class CGlibMeipo implements MethodInterceptor {
public Object getInstance(Class<?> clazz) throws Exception{
//相当于Proxy，代理的工具类
Enhancer enhancer = new Enhancer();
enhancer.setSuperclass(clazz);
enhancer.setCallback(this);
return enhancer.create();
}
public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
before();
Object obj = methodProxy.invokeSuper(o,objects);
after();
return obj;
}
private void before(){
System.out.println("我是媒婆，我要给你找对象，现在已经确认你的需求");
System.out.println("开始物色");
}
private void after(){
System.out.println("OK的话，准备办事");
}
}
测试类
public class CglibTest {
public static void main(String[] args) {
try {
//JDK是采用读取接口的信息
//CGLib覆盖父类方法
//目的：都是生成一个新的类，去实现增强代码逻辑的功能
//JDK Proxy 对于用户而言，必须要有一个接口实现，目标类相对来说复杂
//CGLib 可以代理任意一个普通的类，没有任何要求
//CGLib 生成代理逻辑更复杂，效率,调用效率更高，生成一个包含了所有的逻辑的FastClass，不再需要反射调用
//JDK Proxy生成代理的逻辑简单，执行效率相对要低，每次都要反射动态调用
//CGLib 有个坑，CGLib不能代理final的方法
// 生成class文件
System.setProperty(DebuggingClassWriter.DEBUG_LOCATION_PROPERTY,"E://cglib_proxy_classes");
Customer obj = (Customer) new CGlibMeipo().getInstance(Customer.class);
// System.out.println(obj);
obj.findLove();
} catch (Exception e) {
e.printStackTrace();
}
}
}
代理原理
见注释，可分析生成的class文件得出
通过继承被代理类，复写方法；
