我刚仔细看了Proxy.newProxyInstance的方法注释：
Returns an instance of a proxy class for the specified interfaces that dispatches method invocations to the specified invocation handler. This method is equivalent to: Proxy.getProxyClass(loader, interfaces). // 对应步骤1和2 getConstructor(new Class[] { InvocationHandler.class }). // 对应步骤3 newInstance(new Object[] { handler }); // 对应步骤3其中，第一步，细问一下，class是怎么生成的，很多人估计又答不上了。咱们这里就看一下：
public static Object newProxyInstance(ClassLoader loader, Class<?>[] interfaces, InvocationHandler h) throws IllegalArgumentException { /* * Look up or generate the designated proxy class. */ Class<?> cl = getProxyClass0(loader, interfaces); /* * Invoke its constructor with the designated invocation handler. */ return newInstance(cons, ih); }可以看到，主要的获取Class，是getProxyClass0方法，这个方法里面代码不少，去掉非核心的缓存等部分,核心的部分如下：
String proxyName = proxyPkg + "$Proxy" + num; /* * Generate the specified proxy class. */ byte[] proxyClassFile = ProxyGenerator.generateProxyClass( proxyName, interfaces); proxyClass = defineClass0(loader, proxyName, proxyClassFile, 0, proxyClassFile.length);这其中，ProxyGenerator.generateProxyClass 负责生成class的字节流，对应我们前面讲到的步骤1；defineClass0对应类加载。我们仔细说说：
字节流生成
这部分呢，其实就是调用了ProxyGenerator.generateProxyClass，我们跟踪发现，它的全名为：sun.misc.ProxyGenerator，是sun包下的。这部分没法看源码，还好我之前下载过openjdk的源码，这里我给大家全文贴一下：
/** * 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(); }