动态代理的基本使用就不详细介绍了:
例子:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
|
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
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
|
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
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
|
/** * 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
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
|
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
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
|
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
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
|
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
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
|
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
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
|
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()); } } } |
以上这篇java 1.8 动态代理源码深度分析就是小编分享给大家的全部内容了,希望能给大家一个参考,也希望大家多多支持服务器之家。