tbo*_*odt 39
代理是在运行时创建和加载的类.这些类没有源代码.我知道你想知道如何让他们做一些事情,如果有没有为他们的代码.答案是,当你创建它们,你指定实现目标InvocationHandler,这是定义调用的代理方法时调用的方法.
您可以使用该调用创建它们
Proxy.newProxyInstance(classLoader, interfaces, invocationHandler)
论点是:
classLoader.生成类后,将使用此类加载器加载它.interfaces.必须全部是接口的类对象数组.生成的代理实现所有这些接口.invocationHandler.这是您的代理在调用方法时知道该怎么做的方式.它是一个实现的对象InvocationHandler.当从任何支持的接口的方法,或hashCode,equals或toString,被调用,该方法invoke调用的处理程序中,经过Method用于向被调用的方法和传递的参数对象.有关详细信息,请参阅该Proxy课程的文档.
版本1.3之后的每个JVM实现都必须支持这些.它们被加载到具体实现的方式JVM的内部数据结构,但它是保证工作.
far*_*992 39
没什么特别的.与普通Java类实例一样.
但那些课是Synthetic proxy classes由java.lang.reflect.Proxy#newProxyInstance
1.3中介绍
http://docs.oracle.com/javase/1.3/docs/relnotes/features.html#reflection
它是Java的一部分.所以每个JVM都应该支持它.
简而言之:它们是使用JVM ASM技术创建的(在运行时定义javabyte代码)
使用相同技术的东西:
java.lang.reflect.Proxy#newProxyInstancegetProxyClass0以获取`类
`
ProxyGenerator.generateProxyClass返回字节[] 的魔法define class来加载生成的$ProxyClass(你看到的类名)每个方法都使用相同的字节码构建
invocation handler'sinvoke()invocation handler's 获得返回值invoke()类(字节码)以形式表示 byte[]
如何画一个班级
认为你的java代码被编译成字节码,只需在运行时执行此操作即可
sun/misc/ProxyGenerator.java中的核心方法
generateClassFile
/**
* Generate a class file for the proxy class. This method drives the
* class file generation process.
*/
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.
*/
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.
*/
for (int i = 0; i < interfaces.length; i++) {
Method[] methods = interfaces[i].getMethods();
for (int j = 0; j < methods.length; j++) {
addProxyMethod(methods[j], interfaces[i]);
}
}
/*
* 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 {
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());
}
}
methods.add(generateStaticInitializer());
} catch (IOException e) {
throw new InternalError("unexpected I/O Exception");
}
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 (int i = 0; i < interfaces.length; i++) {
cp.getClass(dotToSlash(interfaces[i].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 {
/*
* 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(ACC_PUBLIC | ACC_FINAL | ACC_SUPER);
// 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 (int i = 0; i < interfaces.length; i++) {
dout.writeShort(cp.getClass(
dotToSlash(interfaces[i].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];
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");
}
return bout.toByteArray();
}
addProxyMethod
/**
* Add another method to be proxied, either by creating a new
* ProxyMethod object or augmenting an old one for a duplicate
* method.
*
* "fromClass" indicates the proxy interface that the method was
* found through, which may be different from (a subinterface of)
* the method's "declaring class". Note that the first Method
* object passed for a given name and descriptor identifies the
* Method object (and thus the declaring class) that will be
* passed to the invocation handler's "invoke" method for a given
* set of duplicate methods.
*/
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<Class<?>>();
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<ProxyMethod>(3);
proxyMethods.put(sig, sigmethods);
}
sigmethods.add(new ProxyMethod(name, parameterTypes, returnType,
exceptionTypes, fromClass));
}
关于gen代理方法的完整代码
private MethodInfo generateMethod() throws IOException {
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);
}
| 归档时间： |
|
| 查看次数： |
84207 次 |
| 最近记录： |