java 1.8 动态代理源码分析
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2022-04-23 10:53:36
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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{
@Overridepublic 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.classConstructor 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CacheKeyObject 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keyObject 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 Factoryif (factory == null) {
factory = new Factory(key, parameter, subKey, valuesMap);
}if (supplier == null) {
supplier = valuesMap.putIfAbsent(subKey, factory);if (supplier == null) {// successfully installed Factorysupplier = factory;
}// else retry with winning supplier} else {if (valuesMap.replace(subKey, supplier, factory)) {// successfully replaced// cleared CacheEntry / unsuccessful Factory// with our Factorysupplier = factory;
} else {// retry with current suppliersupplier = 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 inint 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 packageproxyPkg = 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 objectfields.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());
}
}
}以上就是java 1.8 动态代理源码分析的详细内容，更多请关注其它相关文章！