第一节 参考
问题:
1.创建$Proxy0类源码的位置在哪儿?
2.如果被代理对象实现多个接口,如何区分哪些接口代理，哪些不代理?
第二节 架构
1.在Proxy.newProxyInstance()中创建生成对象,生成对象需要实现目标接口的所有方法。实现方式:
所有方法m1,m2都去调用自己写的代理对象的InvocationHandler.invoke()方法,参数为自己,调用方法Method,参数.
在invoke方法中可以去调用被代理对象的实际方法,并在前后加一些过滤操作.
2.当通过生成对象调用目标接口的方法时,按照1的逻辑运行.
第三节 源码细节
一.创建生成对象
//如果被代理对象实现多个接口,则interfaces传入多个接口
public static Object newProxyInstance(ClassLoader loader,
Class<?>[] interfaces,
InvocationHandler h)
throws IllegalArgumentException
{
//判断代理对象不能空
Objects.requireNonNull(h);
//调用native方法拷贝多个类对象
final Class<?>[] intfs = interfaces.clone();
//对类的方法权限检查
final SecurityManager sm = System.getSecurityManager();
if (sm != null) {
checkProxyAccess(Reflection.getCallerClass(), loader, intfs);
}
/*
* Look up or generate the designated proxy class.
*/
//创建代理类对象
Class<?> cl = getProxyClass0(loader, intfs);
/*
* Invoke its constructor with the designated invocation handler.
*/
try {
if (sm != null) {
checkNewProxyPermission(Reflection.getCallerClass(), cl);
}
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;
}
});
}
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);
}
}二.创建的生成对象的Class文件反编译如下:
public final class $Proxy0
extends Proxy
implements Subject
{
private static Method m1;
private static Method m4;
private static Method m2;
private static Method m3;
private static Method m0;
public $Proxy0(InvocationHandler paramInvocationHandler)
{
super(paramInvocationHandler);
}
public final boolean equals(Object paramObject)
{
try
{
return ((Boolean)this.h.invoke(this, m1, new Object[] { paramObject })).booleanValue();
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}
public final void rent()
{
try
{
this.h.invoke(this, m4, null);
return;
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}
public final String toString()
{
try
{
return (String)this.h.invoke(this, m2, null);
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}
public final void hello(String paramString)
{
try
{
this.h.invoke(this, m3, new Object[] { paramString });
return;
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}
public final int hashCode()
{
try
{
return ((Integer)this.h.invoke(this, m0, null)).intValue();
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}
static
{
try
{
m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[] { Class.forName("java.lang.Object") });
m4 = Class.forName("com.feivirus.dynamicproxy.Subject").getMethod("rent", new Class[0]);
m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
m3 = Class.forName("com.feivirus.dynamicproxy.Subject").getMethod("hello", new Class[] { Class.forName("java.lang.String") });
m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);
return;
}
catch (NoSuchMethodException localNoSuchMethodException)
{
throw new NoSuchMethodError(localNoSuchMethodException.getMessage());
}
catch (ClassNotFoundException localClassNotFoundException)
{
throw new NoClassDefFoundError(localClassNotFoundException.getMessage());
}
}
}三.实际创建生成对象的getProxyClass0()方法
在Proxy.newProxyInstance中进入Proxy#getProxyClass0()后，实际调用ProxyClassFactory#apply()方法创建对象.在apply()中调用
ProxyGenerator#generateProxyClass()方法创建生成对象的字节码.然后调用native()方法Proxy#defineClass0()根据字节码创建Class对象.
(一). 在hotspot中的ProxyGenerator.generateClassFile完成创建字节码操作.
主要逻辑是向ProxyGenerator类的成员变量proxyMethods中添加需要代理的方法.
代码如下:
private byte[] generateClassFile() {
/* ============================================================
* Step 1: Assemble ProxyMethod objects for all methods to
* generate proxy dispatching code for.
*/
/*
* Record that proxy methods are needed for the hashCode, equals,
* and toString methods of java.lang.Object. This is done before
* the methods from the proxy interfaces so that the methods from
* java.lang.Object take precedence over duplicate methods in the
* proxy interfaces.
*/
//向proxyMethods成员变量中添加Object的方法.该方法代码在后面
addProxyMethod(hashCodeMethod, Object.class);
addProxyMethod(equalsMethod, Object.class);
addProxyMethod(toStringMethod, Object.class);
/*
* Now record all of the methods from the proxy interfaces, giving
* earlier interfaces precedence over later ones with duplicate
* methods.
*/
//添加所有代理接口的方法
for (Class<?> intf : interfaces) {
for (Method m : intf.getMethods()) {
addProxyMethod(m, intf);
}
}
/*
* For each set of proxy methods with the same signature,
* verify that the methods' return types are compatible.
*/
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.
*/
try {
//添加InvocationHandler对象的构造方法的字节码
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
//具体创建代理方法的字节码
methods.add(pm.generateMethod());
}
}
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.
*/
/*
* Make sure that constant pool indexes are reserved for the
* following items before starting to write the final class file.
*/
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.
*/
cp.setReadOnly();
ByteArrayOutputStream bout = new ByteArrayOutputStream();
DataOutputStream dout = new DataOutputStream(bout);
try {
//写入class文件的文件头
/*
* Write all the items of the "ClassFile" structure.
* See JVMS section 4.1.
*/
// u4 magic;
dout.writeInt(0xCAFEBABE);
// u2 minor_version;
dout.writeShort(CLASSFILE_MINOR_VERSION);
// u2 major_version;
dout.writeShort(CLASSFILE_MAJOR_VERSION);
cp.write(dout); // (write constant pool)
// u2 access_flags;
dout.writeShort(accessFlags);
// u2 this_class;
dout.writeShort(cp.getClass(dotToSlash(className)));
// u2 super_class;
dout.writeShort(cp.getClass(superclassName));
// u2 interfaces_count;
dout.writeShort(interfaces.length);
// u2 interfaces[interfaces_count];
for (Class<?> intf : interfaces) {
dout.writeShort(cp.getClass(
dotToSlash(intf.getName())));
}
// u2 fields_count;
dout.writeShort(fields.size());
// field_info fields[fields_count];
for (FieldInfo f : fields) {
f.write(dout);
}
// u2 methods_count;
dout.writeShort(methods.size());
// method_info methods[methods_count];
//写入具体的代理方法字节码
for (MethodInfo m : methods) {
m.write(dout);
}
// u2 attributes_count;
dout.writeShort(0); // (no ClassFile attributes for proxy classes)
} catch (IOException e) {
throw new InternalError("unexpected I/O Exception", e);
}
return bout.toByteArray();
}(二).创建生成对象的代理方法字节码.
ProxyGenerator.addProxyMethod
private void addProxyMethod(Method m, Class<?> fromClass) {
String name = m.getName();
Class<?>[] parameterTypes = m.getParameterTypes();
Class<?> returnType = m.getReturnType();
Class<?>[] exceptionTypes = m.getExceptionTypes();
String sig = name + getParameterDescriptors(parameterTypes);
List<ProxyMethod> sigmethods = proxyMethods.get(sig);
if (sigmethods != null) {
for (ProxyMethod pm : sigmethods) {
if (returnType == pm.returnType) {
/*
* Found a match: reduce exception types to the
* greatest set of exceptions that can thrown
* compatibly with the throws clauses of both
* overridden methods.
*/
List<Class<?>> legalExceptions = new ArrayList<>();
collectCompatibleTypes(
exceptionTypes, pm.exceptionTypes, legalExceptions);
collectCompatibleTypes(
pm.exceptionTypes, exceptionTypes, legalExceptions);
pm.exceptionTypes = new Class<?>[legalExceptions.size()];
pm.exceptionTypes =
legalExceptions.toArray(pm.exceptionTypes);
return;
}
}
} else {
sigmethods = new ArrayList<>(3);
proxyMethods.put(sig, sigmethods);
}
sigmethods.add(new ProxyMethod(name, parameterTypes, returnType,
exceptionTypes, fromClass));
} (三).生成代理方法的字节码的方法
ProxyMethod.generateMethod()方法
private MethodInfo generateMethod() throws IOException {
//获取方法的描述符
String desc = getMethodDescriptor(parameterTypes, returnType);
MethodInfo minfo = new MethodInfo(methodName, desc,
ACC_PUBLIC | ACC_FINAL);
int[] parameterSlot = new int[parameterTypes.length];
int nextSlot = 1;
for (int i = 0; i < parameterSlot.length; i++) {
parameterSlot[i] = nextSlot;
nextSlot += getWordsPerType(parameterTypes[i]);
}
int localSlot0 = nextSlot;
short pc, tryBegin = 0, tryEnd;
DataOutputStream out = new DataOutputStream(minfo.code);
code_aload(0, out);
out.writeByte(opc_getfield);
out.writeShort(cp.getFieldRef(
superclassName,
handlerFieldName, "Ljava/lang/reflect/InvocationHandler;"));
code_aload(0, out);
out.writeByte(opc_getstatic);
out.writeShort(cp.getFieldRef(
dotToSlash(className),
methodFieldName, "Ljava/lang/reflect/Method;"));
if (parameterTypes.length > 0) {
code_ipush(parameterTypes.length, out);
out.writeByte(opc_anewarray);
out.writeShort(cp.getClass("java/lang/Object"));
for (int i = 0; i < parameterTypes.length; i++) {
out.writeByte(opc_dup);
code_ipush(i, out);
codeWrapArgument(parameterTypes[i], parameterSlot[i], out);
out.writeByte(opc_aastore);
}
} else {
out.writeByte(opc_aconst_null);
}
out.writeByte(opc_invokeinterface);
out.writeShort(cp.getInterfaceMethodRef(
"java/lang/reflect/InvocationHandler",
"invoke",
"(Ljava/lang/Object;Ljava/lang/reflect/Method;" +
"[Ljava/lang/Object;)Ljava/lang/Object;"));
out.writeByte(4);
out.writeByte(0);
if (returnType == void.class) {
out.writeByte(opc_pop);
out.writeByte(opc_return);
} else {
codeUnwrapReturnValue(returnType, out);
}
tryEnd = pc = (short) minfo.code.size();
List<Class<?>> catchList = computeUniqueCatchList(exceptionTypes);
if (catchList.size() > 0) {
for (Class<?> ex : catchList) {
minfo.exceptionTable.add(new ExceptionTableEntry(
tryBegin, tryEnd, pc,
cp.getClass(dotToSlash(ex.getName()))));
}
out.writeByte(opc_athrow);
pc = (short) minfo.code.size();
minfo.exceptionTable.add(new ExceptionTableEntry(
tryBegin, tryEnd, pc, cp.getClass("java/lang/Throwable")));
code_astore(localSlot0, out);
out.writeByte(opc_new);
out.writeShort(cp.getClass(
"java/lang/reflect/UndeclaredThrowableException"));
out.writeByte(opc_dup);
code_aload(localSlot0, out);
out.writeByte(opc_invokespecial);
out.writeShort(cp.getMethodRef(
"java/lang/reflect/UndeclaredThrowableException",
"<init>", "(Ljava/lang/Throwable;)V"));
out.writeByte(opc_athrow);
}
if (minfo.code.size() > 65535) {
throw new IllegalArgumentException("code size limit exceeded");
}
minfo.maxStack = 10;
minfo.maxLocals = (short) (localSlot0 + 1);
minfo.declaredExceptions = new short[exceptionTypes.length];
for (int i = 0; i < exceptionTypes.length; i++) {
minfo.declaredExceptions[i] = cp.getClass(
dotToSlash(exceptionTypes[i].getName()));
}
return minfo;
}(四).Proxy.defineClass0的native方法代码
根据内存中的字节码，创建class对象
进入Unsafe.Unsafe_DefineClass_impl()方法中.最终进入jvm.cpp的jvm_define_class_common()方法.代码如下:
static jclass jvm_define_class_common(JNIEnv *env, const char *name,
jobject loader, const jbyte *buf,
jsize len, jobject pd, const char *source,
jboolean verify, TRAPS) {
if (source == NULL) source = "__JVM_DefineClass__";
assert(THREAD->is_Java_thread(), "must be a JavaThread");
JavaThread* jt = (JavaThread*) THREAD;
PerfClassTraceTime vmtimer(ClassLoader::perf_define_appclass_time(),
ClassLoader::perf_define_appclass_selftime(),
ClassLoader::perf_define_appclasses(),
jt->get_thread_stat()->perf_recursion_counts_addr(),
jt->get_thread_stat()->perf_timers_addr(),
PerfClassTraceTime::DEFINE_CLASS);
if (UsePerfData) {
ClassLoader::perf_app_classfile_bytes_read()->inc(len);
}
// Since exceptions can be thrown, class initialization can take place
// if name is NULL no check for class name in .class stream has to be made.
TempNewSymbol class_name = NULL;
if (name != NULL) {
const int str_len = (int)strlen(name);
if (str_len > Symbol::max_length()) {
// It's impossible to create this class; the name cannot fit
// into the constant pool.
THROW_MSG_0(vmSymbols::java_lang_NoClassDefFoundError(), name);
}
class_name = SymbolTable::new_symbol(name, str_len, CHECK_NULL);
}
ResourceMark rm(THREAD);
//创建classfile的文件
ClassFileStream st((u1*) buf, len, (char *)source);
Handle class_loader (THREAD, JNIHandles::resolve(loader));
if (UsePerfData) {
is_lock_held_by_thread(class_loader,
ClassLoader::sync_JVMDefineClassLockFreeCounter(),
THREAD);
}
Handle protection_domain (THREAD, JNIHandles::resolve(pd));
//解析成Kclass结构
Klass* k = SystemDictionary::resolve_from_stream(class_name, class_loader,
protection_domain, &st,
verify != 0,
CHECK_NULL);
if (TraceClassResolution && k != NULL) {
trace_class_resolution(k);
}
return (jclass) JNIHandles::make_local(env, k->java_mirror());
}
