1. 静态代理
1.1 定义：代理模式给某一个对象提供一个代理对象，并由代理对象控制对原对象的引用。通俗的来讲代理模式就是我们生活 中常见的中介。
1.2 目的：
1.3 角色介绍：
- 抽象角色：指代理角色和真实角色对外提供的公共方法，一般为一个接口
- 真实角色：需要实现抽象角色接口，定义了真实角色所要实现的业务逻辑，以便供代理角色调用。也就是真正的业 务逻辑在此。
- 代理角色：需要实现抽象角色接口，是真实角色的代理，通过真实角色的业务逻辑方法来实现抽象方法，并可以附加自己的操作。将统一的流程控制都放到代理角色中处理！
1.4 使用样例代码：
以下是代理接口，该接口定义保存订单功能。
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| public interface OrderService {
int saveOrder();
}
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以下是真实实现类。
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| public class OutOrderServiceImpl implements OrderService {
@Override
public int saveOrder() {
System.out.println("下单成功，订单号： 66666666");
return 66666666;
}
}
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以下是代理类，代理持有真实实现类的对象，可以流程进行控制。
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| public class ProxyOrder implements OrderService {
private OrderService orderService = new OutOrderServiceImpl();
private void setOrderTag() {
System.out.println("开始海外下订单");
}
@Override
public int saveOrder() {
setOrderTag();
return orderService.saveOrder();
}
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2.动态代理
2.1 定义：通过反射机制，在运行时创建代理类
2.2 使用：
创建代理类，持有真实实现
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| public class ProxyHandler implements InvocationHandler {
private OrderService service;
public ProxyHandler(OrderService service) {
this.service = service;
}
@Override
public Object invoke(Object o, Method method, Object[] objects) throws Throwable {
System.out.println("before invoke -->");
method.invoke(service, objects);
System.out.println("after invoke -->");
return null;
}
}
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使用动态代理调用方法
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| public static void main(String[] args) {
OrderService service = new OutOrderServiceImpl();
OrderService proxy = (OrderService)Proxy.newProxyInstance(
service.getClass().getClassLoader(),
service.getClass().getInterfaces(),
new ProxyHandler(service));
proxy.saveOrder();
}
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2.3 动态代理原理：
- 通过用户实现的InvocationHandler接口，获得真实处理事件的对象（相当于Proxy加了个传入真实实现对象监听）；
- 通过newProxyInstance传入的ClassLoader和一组Interface来创建动态代理类；
- 通过反射获取动态代理类的构造方法，其构造函数的参数就是用户实现的InvocationHandler接口类；
- 通过构造函数创建动态代理类实例。
==============================生成动态代理类=============================================
下面我们详细来看一下Proxy是如何生成代理对象的。
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| public static Object newProxyInstance(ClassLoader loader,
Class<?>[] interfaces,
InvocationHandler h)
throws IllegalArgumentException
{
Objects.requireNonNull(h);
final Class<?>[] intfs = interfaces.clone();
Class<?> cl = getProxyClass0(loader, intfs);
try {
final Constructor<?> cons = cl.getConstructor(constructorParams);
final InvocationHandler ih = h;
if (!Modifier.isPublic(cl.getModifiers())) {
cons.setAccessible(true);
}
return cons.newInstance(new Object[]{h});
} catch (IllegalAccessException|InstantiationException e) {
}
}
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下面我们来看一下是如何生成这个Class对象的
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| private static Class<?> getProxyClass0(ClassLoader loader,
Class<?>... interfaces) {
if (interfaces.length > 65535) {
throw new IllegalArgumentException("interface limit exceeded");
}
return proxyClassCache.get(loader, interfaces);
}
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下面来看一下ProxyClassFactory是如何创建代理对象的。(在Proxy中有一个ProxyClassFactory静态内部类)
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| public Class<?> apply(ClassLoader loader, Class<?>[] interfaces) {
Map<Class<?>, Boolean> interfaceSet = new IdentityHashMap<>(interfaces.length);
for (Class<?> intf : interfaces) {
Class<?> interfaceClass = null;
try {
interfaceClass = Class.forName(intf.getName(), false, loader);
} catch (ClassNotFoundException e) {
}
if (interfaceClass != intf) {
throw new IllegalArgumentException(
intf + " is not visible from class loader");
}
if (!interfaceClass.isInterface()) {
throw new IllegalArgumentException(
interfaceClass.getName() + " is not an interface");
}
if (interfaceSet.put(interfaceClass, Boolean.TRUE) != null) {
throw new IllegalArgumentException(
"repeated interface: " + interfaceClass.getName());
}
}
String proxyPkg = null;
int accessFlags = Modifier.PUBLIC | Modifier.FINAL;
for (Class<?> intf : interfaces) {
int flags = intf.getModifiers();
if (!Modifier.isPublic(flags)) {
accessFlags = Modifier.FINAL;
String name = intf.getName();
int n = name.lastIndexOf('.');
String pkg = ((n == -1) ? "" : name.substring(0, n + 1));
if (proxyPkg == null) {
proxyPkg = pkg;
} else if (!pkg.equals(proxyPkg)) {
throw new IllegalArgumentException(
"non-public interfaces from different packages");
}
}
}
if (proxyPkg == null) {
proxyPkg = "";
}
{
List<Method> methods = getMethods(interfaces);
Collections.sort(methods, ORDER_BY_SIGNATURE_AND_SUBTYPE);
validateReturnTypes(methods);
List<Class<?>[]> exceptions = deduplicateAndGetExceptions(methods);
Method[] methodsArray = methods.toArray(new Method[methods.size()]);
Class<?>[][] exceptionsArray = exceptions.toArray(new Class<?>[exceptions.size()][]);
long num = nextUniqueNumber.getAndIncrement();
String proxyName = proxyPkg + proxyClassNamePrefix + num;
return generateProxy(proxyName, interfaces, loader, methodsArray,
exceptionsArray);
}
}
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最后通过调用native的generateProxy()方法生成class类
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| private static native Class<?> generateProxy(String name, Class<?>[] interfaces,
ClassLoader loader, Method[] methods,
Class<?>[][] exceptions);
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在Android中生成class类是在navite中生成的。在java中最终是调用ProxyGenerator.generateProxyClass()生成byte数组，最后调用defineClass0()将byte数组转化成class类
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| public static byte[] generateProxyClass(final String var0, Class<?>[] var1, int var2) {
ProxyGenerator var3 = new ProxyGenerator(var0, var1, var2);
final byte[] var4 = var3.generateClassFile();
if(saveGeneratedFiles) {
AccessController.doPrivileged(new PrivilegedAction<Void>() {
public Void run() {
try {
int var1 = var0.lastIndexOf(46);
Path var2;
if(var1 > 0) {
Path var3 = Paths.get(var0.substring(0, var1).replace('.', File.separatorChar), new String[0]);
Files.createDirectories(var3, new FileAttribute[0]);
var2 = var3.resolve(var0.substring(var1 + 1, var0.length()) + ".class");
} else {
var2 = Paths.get(var0 + ".class", new String[0]);
}
Files.write(var2, var4, new OpenOption[0]);
return null;
} catch (IOException var4x) {
throw new InternalError("I/O exception saving generated file: " + var4x);
}
}
});
}
return var4;
}
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生成代理类字节码文件的generateClassFile方法：
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| private byte[] generateClassFile() {
this.addProxyMethod(hashCodeMethod, Object.class);
this.addProxyMethod(equalsMethod, Object.class);
this.addProxyMethod(toStringMethod, Object.class);
Class[] var1 = this.interfaces;
int var2 = var1.length;
int var3;
Class var4;
for(var3 = 0; var3 < var2; ++var3) {
var4 = var1[var3];
Method[] var5 = var4.getMethods();
int var6 = var5.length;
for(int var7 = 0; var7 < var6; ++var7) {
Method var8 = var5[var7];
this.addProxyMethod(var8, var4);
}
}
Iterator var11 = this.proxyMethods.values().iterator();
List var12;
while(var11.hasNext()) {
var12 = (List)var11.next();
checkReturnTypes(var12);
}
Iterator var15;
try {
this.methods.add(this.generateConstructor());
var11 = this.proxyMethods.values().iterator();
while(var11.hasNext()) {
var12 = (List)var11.next();
var15 = var12.iterator();
while(var15.hasNext()) {
ProxyGenerator.ProxyMethod var16 = (ProxyGenerator.ProxyMethod)var15.next();
this.fields.add(new ProxyGenerator.FieldInfo(var16.methodFieldName, "Ljava/lang/reflect/Method;", 10));
this.methods.add(var16.generateMethod());
}
}
this.methods.add(this.generateStaticInitializer());
} catch (IOException var10) {
throw new InternalError("unexpected I/O Exception", var10);
}
if(this.methods.size() > '\uffff') {
throw new IllegalArgumentException("method limit exceeded");
} else if(this.fields.size() > '\uffff') {
throw new IllegalArgumentException("field limit exceeded");
} else {
this.cp.getClass(dotToSlash(this.className));
this.cp.getClass("java/lang/reflect/Proxy");
var1 = this.interfaces;
var2 = var1.length;
for(var3 = 0; var3 < var2; ++var3) {
var4 = var1[var3];
this.cp.getClass(dotToSlash(var4.getName()));
}
this.cp.setReadOnly();
ByteArrayOutputStream var13 = new ByteArrayOutputStream();
DataOutputStream var14 = new DataOutputStream(var13);
try {
var14.writeInt(-889275714);
var14.writeShort(0);
var14.writeShort(49);
this.cp.write(var14);
var14.writeShort(this.accessFlags);
var14.writeShort(this.cp.getClass(dotToSlash(this.className)));
var14.writeShort(this.cp.getClass("java/lang/reflect/Proxy"));
var14.writeShort(this.interfaces.length);
Class[] var17 = this.interfaces;
int var18 = var17.length;
for(int var19 = 0; var19 < var18; ++var19) {
Class var22 = var17[var19];
var14.writeShort(this.cp.getClass(dotToSlash(var22.getName())));
}
var14.writeShort(this.fields.size());
var15 = this.fields.iterator();
while(var15.hasNext()) {
ProxyGenerator.FieldInfo var20 = (ProxyGenerator.FieldInfo)var15.next();
var20.write(var14);
}
var14.writeShort(this.methods.size());
var15 = this.methods.iterator();
while(var15.hasNext()) {
ProxyGenerator.MethodInfo var21 = (ProxyGenerator.MethodInfo)var15.next();
var21.write(var14);
}
var14.writeShort(0);
return var13.toByteArray();
} catch (IOException var9) {
throw new InternalError("unexpected I/O Exception", var9);
}
}
}
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调用generateClassFile()之后，就会生成class类的byte数组。
为了验证这个结论，写一个demo：
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| private static void proxy() throws Exception {
String name = OrderService.class.getName() + "$Proxy0";
byte[] bytes = ProxyGenerator.generateProxyClass(name, new Class[]{OrderService.class});
FileOutputStream fos = new FileOutputStream("C:\\Users\\gz04766\\Desktop\\" + name + ".class");
fos.write(bytes);
fos.close();
}
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至此，我们分析清楚了Proxy是如何生成代理class类的。
================================如何完成动态调用========================================
当通过反射调用构造方法的时候，将用户实现的InvocationHandler传给Proxy。在生成的类中，通过反射拿到接口定义的Method方法。最后通过父类的中的InvocationHandler的invoke方法，最终调入到自定义的InvocationHandler中。
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public final class OrderService$Proxy0 extends Proxy implements OrderService {
private static Method m1;
private static Method m3;
private static Method m2;
private static Method m0;
public OrderService$Proxy0(InvocationHandler var1) throws {
super(var1);
}
public final int saveOrder() throws {
try {
return (Integer)super.h.invoke(this, m3, (Object[])null);
} catch (RuntimeException | Error var2) {
throw var2;
} catch (Throwable var3) {
throw new UndeclaredThrowableException(var3);
}
}
static {
try {
m1 = Class.forName("java.lang.Object").getMethod("equals", Class.forName("java.lang.Object"));
m3 = Class.forName("com.gac.oj.OrderService").getMethod("saveOrder");
m2 = Class.forName("java.lang.Object").getMethod("toString");
m0 = Class.forName("java.lang.Object").getMethod("hashCode");
} catch (NoSuchMethodException var2) {
throw new NoSuchMethodError(var2.getMessage());
} catch (ClassNotFoundException var3) {
throw new NoClassDefFoundError(var3.getMessage());
}
}
.....
}
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