JDK8动态代理源码分析
动态代理的基本使用就不详细介绍了：
例子：
class proxyed implements pro{
@Override
public void text() {
System.err.println("本方法");
}
}
interface pro {
void text();
}
public class JavaProxy implements InvocationHandler {
private Object source;
public JavaProxy(Object source) {
super();
this.source = source;
}
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
System.out.println("before");
Object invoke = method.invoke(source, args);
System.out.println("after");
return invoke;
}
public Object getProxy(){
return Proxy.newProxyInstance(getClass().getClassLoader(), source.getClass().getInterfaces(), this);
}
public static void main(String[] args) throws IllegalAccessException, InvocationTargetException, InstantiationException, NoSuchMethodException {
//第一种，自己写
//1.设置saveGeneratedFiles值为true则生成 class字节码文件方便分析
System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", "true");
//2.获取动态代理类
Class proxyClazz = Proxy.getProxyClass(pro.class.getClassLoader(),pro.class);
//3.获得代理类的构造函数，并传入参数类型InvocationHandler.class
Constructor constructor = proxyClazz.getConstructor(InvocationHandler.class);
//4.通过构造函数来创建动态代理对象，将自定义的InvocationHandler实例传入
pro iHello = (pro) constructor.newInstance(new JavaProxy(new proxyed()));
//5.通过代理对象调用目标方法
iHello.text();
//第二种，调用JDK提供的方法，实现了2~4步
Proxy.newProxyInstance(JavaProxy.class.getClassLoader(),proxyed.class.getInterfaces(),new JavaProxy(new proxyed()));
}
}
入口：newProxyInstance
public static Object newProxyInstance(ClassLoader loader, Class<?>[] interfaces, InvocationHandler h) throws IllegalArgumentException {
//Objects.requireNonNull 判空方法，之后所有的单纯的判断null并抛异常，都是此方法
Objects.requireNonNull(h);
//clone 类实现的所有接口
final Class<?>[] intfs = interfaces.clone();
//获取当前系统安全接口
final SecurityManager sm = System.getSecurityManager();
if (sm != null) {
//Reflection.getCallerClass返回调用该方法的方法的调用类;loader：接口的类加载器
//进行包访问权限、类加载器权限等检查
checkProxyAccess(Reflection.getCallerClass(), loader, intfs);
}
/*
* Look up or generate the designated proxy class.
* 查找或生成代理类
*/
Class<?> cl = getProxyClass0(loader, intfs);
/*
* Invoke its constructor with the designated invocation handler.
* 使用指定的调用处理程序调用它的构造函数
*/
try {
if (sm != null) {
checkNewProxyPermission(Reflection.getCallerClass(), cl);
}
//获取构造
final Constructor<?> cons = cl.getConstructor(constructorParams);
final InvocationHandler ih = h;
if (!Modifier.isPublic(cl.getModifiers())) {
AccessController.doPrivileged(new PrivilegedAction<Void>() {
public Void run() {
cons.setAccessible(true);
return null;
}
});
}
//返回 代理对象
return cons.newInstance(new Object[]{h});
} catch (IllegalAccessException|InstantiationException e) {
throw new InternalError(e.toString(), e);
} catch (InvocationTargetException e) {
Throwable t = e.getCause();
if (t instanceof RuntimeException) {
throw (RuntimeException) t;
} else {
throw new InternalError(t.toString(), t);
}
} catch (NoSuchMethodException e) {
throw new InternalError(e.toString(), e);
}
}
从上面的分析中可以看出，newProxyInstance帮我们执行了生成代理类----获取构造器----生成代理对象这三步；
我们重点分析生成代理类
getProxyClass0
/**
* a cache of proxy classes：动态代理类的弱缓存容器
* KeyFactory:根据接口的数量，映射一个最佳的key生成函数,其中表示接口的类对象被弱引用；也就是key对象被弱引用继承自WeakReference（key0、key1、key2、keyX），保存接口密钥(hash值)
* ProxyClassFactory：生成动态类的工厂
* 注意，两个都实现了BiFunction<ClassLoader, Class<?>[], Object>接口
*/
private static final WeakCache<ClassLoader, Class<?>[], Class<?>> proxyClassCache = new WeakCache<>(new KeyFactory(), new ProxyClassFactory()); /**
* Generate a proxy class. Must call the checkProxyAccess method
* to perform permission checks before calling this.
* 生成代理类，调用前必须进行 checkProxyAccess权限检查，所以newProxyInstance进行了权限检查
*/
private static Class<?> getProxyClass0(ClassLoader loader, Class<?>... interfaces) {
//实现接口的最大数量<65535;谁写的类能实现这么多接口
if (interfaces.length > 65535) {
throw new IllegalArgumentException("interface limit exceeded");
} // If the proxy class defined by the given loader implementing
// the given interfaces exists, this will simply return the cached copy;
// otherwise, it will create the proxy class via the ProxyClassFactory
// 如果缓存中有，就直接返回，否则会生成
return proxyClassCache.get(loader, interfaces);
}
proxyClassCache.get
public V get(K key, P parameter) {
//key：类加载器；parameter：接口数组
Objects.requireNonNull(parameter);
//清除已经被GC回收的弱引用
expungeStaleEntries();
//CacheKey弱引用类，refQueue已经被回收的弱引用队列；构建一个CacheKey
Object cacheKey = CacheKey.valueOf(key, refQueue);
//map一级缓存，获取valuesMap二级缓存
ConcurrentMap<Object, Supplier<V>> valuesMap = map.get(cacheKey);
if (valuesMap == null) {
ConcurrentMap<Object, Supplier<V>> oldValuesMap
= map.putIfAbsent(cacheKey,
valuesMap = new ConcurrentHashMap<>());
if (oldValuesMap != null) {
valuesMap = oldValuesMap;
}
}
// subKeyFactory类型是KeyFactory，apply返回表示接口的key
Object subKey = Objects.requireNonNull(subKeyFactory.apply(key, parameter));
//Factory 实现了supplier，我们实际是获取缓存中的Factory，调用其get方法
Supplier<V> supplier = valuesMap.get(subKey);
Factory factory = null;
//下面用到了 CAS+重试 实现的多线程安全的 非阻塞算法
while (true) {
if (supplier != null) {
// 只需要知道，最终会调用get方法，此supplier可能是缓存中取出来的，也可能是Factory新new出来的
V value = supplier.get();
if (value != null) {
return value;
}
}
// else no supplier in cache
// or a supplier that returned null (could be a cleared CacheValue
// or a Factory that wasn't successful in installing the CacheValue)
// lazily construct a Factory
if (factory == null) {
factory = new Factory(key, parameter, subKey, valuesMap);
}
if (supplier == null) {
supplier = valuesMap.putIfAbsent(subKey, factory);
if (supplier == null) {
// successfully installed Factory
supplier = factory;
}
// else retry with winning supplier
} else {
if (valuesMap.replace(subKey, supplier, factory)) {
// successfully replaced
// cleared CacheEntry / unsuccessful Factory
// with our Factory
supplier = factory;
} else {
// retry with current supplier
supplier = valuesMap.get(subKey);
}
}
}
}
supplier.get
这个方法中会调用ProxyClassFactory的apply方法，就不过多介绍
ProxyClassFactory.apply
public Class<?> apply(ClassLoader loader, Class<?>[] interfaces) {
Map<Class<?>, Boolean> interfaceSet = new IdentityHashMap<>(interfaces.length);
for (Class<?> intf : interfaces) {
/*
* Verify that the class loader resolves the name of this interface to the same Class object.
* 类加载器和接口名解析出的是同一个
*/
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");
}
/*
* Verify that the Class object actually represents an interface.
* 确保是一个接口
*/
if (!interfaceClass.isInterface()) {
throw new IllegalArgumentException( interfaceClass.getName() + " is not an interface");
}
/*
* Verify that this interface is not a duplicate.
* 确保接口没重复
*/
if (interfaceSet.put(interfaceClass, Boolean.TRUE) != null) {
throw new IllegalArgumentException( "repeated interface: " + interfaceClass.getName());
}
}
String proxyPkg = null; // package to define proxy class in
int accessFlags = Modifier.PUBLIC | Modifier.FINAL;
/*
* Record the package of a non-public proxy interface so that the proxy class will be defined in the same package.
* Verify that all non-public proxy interfaces are in the same package.
* 验证所有非公共的接口在同一个包内；公共的就无需处理
*/
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) {
// if no non-public proxy interfaces, use com.sun.proxy package
proxyPkg = ReflectUtil.PROXY_PACKAGE + ".";
}
/*
* Choose a name for the proxy class to generate.
* proxyClassNamePrefix = $Proxy
* nextUniqueNumber 是一个原子类，确保多线程安全，防止类名重复，类似于：$Proxy0，$Proxy1......
*/
long num = nextUniqueNumber.getAndIncrement();
String proxyName = proxyPkg + proxyClassNamePrefix + num;
/*
* Generate the specified proxy class.
* 生成类字节码的方法:重点
*/
byte[] proxyClassFile = ProxyGenerator.generateProxyClass( proxyName, interfaces, accessFlags);
try {
return defineClass0(loader, proxyName, proxyClassFile, 0, proxyClassFile.length);
} catch (ClassFormatError e) {
/*
* A ClassFormatError here means that (barring bugs in the
* proxy class generation code) there was some other
* invalid aspect of the arguments supplied to the proxy
* class creation (such as virtual machine limitations
* exceeded).
*/
throw new IllegalArgumentException(e.toString());
}
}
ProxyGenerator.generateProxyClass
public static byte[] generateProxyClass(final String name, Class<?>[] interfaces, int accessFlags) {
ProxyGenerator gen = new ProxyGenerator(name, interfaces, accessFlags);
//真正生成字节码的方法
final byte[] classFile = gen.generateClassFile();
//如果saveGeneratedFiles为true 则生成字节码文件，所以在开始我们要设置这个参数
//当然，也可以通过返回的bytes自己输出
if (saveGeneratedFiles) {
java.security.AccessController.doPrivileged( new java.security.PrivilegedAction<Void>() {
public Void run() {
try {
int i = name.lastIndexOf('.');
Path path;
if (i > 0) {
Path dir = Paths.get(name.substring(0, i).replace('.', File.separatorChar));
Files.createDirectories(dir);
path = dir.resolve(name.substring(i+1, name.length()) + ".class");
} else {
path = Paths.get(name + ".class");
}
Files.write(path, classFile);
return null;
} catch (IOException e) {
throw new InternalError( "I/O exception saving generated file: " + e);
}
}
});
}
return classFile;
}
最终方法
private byte[] generateClassFile() {
/* ============================================================
* Step 1: Assemble ProxyMethod objects for all methods to generate proxy dispatching code for.
* 步骤1：为所有方法生成代理调度代码，将代理方法对象集合起来。
*/
//增加 hashcode、equals、toString方法
addProxyMethod(hashCodeMethod, Object.class);
addProxyMethod(equalsMethod, Object.class);
addProxyMethod(toStringMethod, Object.class);
//增加接口方法
for (Class<?> intf : interfaces) {
for (Method m : intf.getMethods()) {
addProxyMethod(m, intf);
}
}
/*
* 验证方法签名相同的一组方法，返回值类型是否相同；意思就是重写方法要方法签名和返回值一样
*/
for (List<ProxyMethod> sigmethods : proxyMethods.values()) {
checkReturnTypes(sigmethods);
}
/* ============================================================
* Step 2: Assemble FieldInfo and MethodInfo structs for all of fields and methods in the class we are generating.
* 为类中的方法生成字段信息和方法信息
*/
try {
//增加构造方法
methods.add(generateConstructor());
for (List<ProxyMethod> sigmethods : proxyMethods.values()) {
for (ProxyMethod pm : sigmethods) {
// add static field for method's Method object
fields.add(new FieldInfo(pm.methodFieldName,
"Ljava/lang/reflect/Method;",
ACC_PRIVATE | ACC_STATIC));
// generate code for proxy method and add it
methods.add(pm.generateMethod());
}
}
//增加静态初始化信息
methods.add(generateStaticInitializer());
} catch (IOException e) {
throw new InternalError("unexpected I/O Exception", e);
}
if (methods.size() > 65535) {
throw new IllegalArgumentException("method limit exceeded");
}
if (fields.size() > 65535) {
throw new IllegalArgumentException("field limit exceeded");
}
/* ============================================================
* Step 3: Write the final class file.
* 步骤3：编写最终类文件
*/
/*
* Make sure that constant pool indexes are reserved for the following items before starting to write the final class file.
* 在开始编写最终类文件之前，确保为下面的项目保留常量池索引。
*/
cp.getClass(dotToSlash(className));
cp.getClass(superclassName);
for (Class<?> intf: interfaces) {
cp.getClass(dotToSlash(intf.getName()));
}
/*
* Disallow new constant pool additions beyond this point, since we are about to write the final constant pool table.
* 设置只读，在这之前不允许在常量池中增加信息，因为要写常量池表
*/
cp.setReadOnly();
ByteArrayOutputStream bout = new ByteArrayOutputStream();
DataOutputStream dout = new DataOutputStream(bout);
try {
// u4 magic;
dout.writeInt(0xCAFEBABE);
// u2 次要版本;
dout.writeShort(CLASSFILE_MINOR_VERSION);
// u2 主版本
dout.writeShort(CLASSFILE_MAJOR_VERSION);
cp.write(dout); // (write constant pool)
// u2 访问标识;
dout.writeShort(accessFlags);
// u2 本类名;
dout.writeShort(cp.getClass(dotToSlash(className)));
// u2 父类名;
dout.writeShort(cp.getClass(superclassName));
// u2 接口;
dout.writeShort(interfaces.length);
// u2 interfaces[interfaces_count];
for (Class<?> intf : interfaces) {
dout.writeShort(cp.getClass(
dotToSlash(intf.getName())));
}
// u2 字段;
dout.writeShort(fields.size());
// field_info fields[fields_count];
for (FieldInfo f : fields) {
f.write(dout);
}
// u2 方法;
dout.writeShort(methods.size());
// method_info methods[methods_count];
for (MethodInfo m : methods) {
m.write(dout);
}
// u2 类文件属性：对于代理类来说没有类文件属性;
dout.writeShort(0); // (no ClassFile attributes for proxy classes)
} catch (IOException e) {
throw new InternalError("unexpected I/O Exception", e);
}
return bout.toByteArray();
}
生成的字节码反编译
final class $Proxy0 extends Proxy implements pro {
//fields
private static Method m1;
private static Method m2;
private static Method m3;
private static Method m0;
public $Proxy0(InvocationHandler var1) throws {
super(var1);
}
public final boolean equals(Object var1) throws {
try {
return ((Boolean)super.h.invoke(this, m1, new Object[]{var1})).booleanValue();
} catch (RuntimeException | Error var3) {
throw var3;
} catch (Throwable var4) {
throw new UndeclaredThrowableException(var4);
}
}
public final String toString() throws {
try {
return (String)super.h.invoke(this, m2, (Object[])null);
} catch (RuntimeException | Error var2) {
throw var2;
} catch (Throwable var3) {
throw new UndeclaredThrowableException(var3);
}
}
public final void text() throws {
try {
//实际就是调用代理类的invoke方法
super.h.invoke(this, m3, (Object[])null);
} catch (RuntimeException | Error var2) {
throw var2;
} catch (Throwable var3) {
throw new UndeclaredThrowableException(var3);
}
}
public final int hashCode() throws {
try {
return ((Integer)super.h.invoke(this, m0, (Object[])null)).intValue();
} catch (RuntimeException | Error var2) {
throw var2;
} catch (Throwable var3) {
throw new UndeclaredThrowableException(var3);
}
}
static {
try {
//这里每个方法对象 和类的实际方法绑定
m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[]{Class.forName("java.lang.Object")});
m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
m3 = Class.forName("spring.commons.api.study.CreateModel.pro").getMethod("text", new Class[0]);
m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);
} catch (NoSuchMethodException var2) {
throw new NoSuchMethodError(var2.getMessage());
} catch (ClassNotFoundException var3) {
throw new NoClassDefFoundError(var3.getMessage());
}
}
}