0. 疫情让我想要保存几家村里面的外卖电话
1. JDK代理类的创建过程
1.1 JdkDynamicAopProxy 创建
public Object getProxy(@Nullable ClassLoader classLoader) {
return
// 其实，我们刚从这里出来，并返回了一个 AopProxy
createAopProxy()
// step into ...
// 也就是说接下来我们分析的代理bean的创建只需跟踪JDK、cegLib的AopProxy的构造方法以及getProxy()即可
.getProxy(classLoader);
}
public JdkDynamicAopProxy(AdvisedSupport config) throws AopConfigException {
Assert.notNull(config, "AdvisedSupport must not be null");
if (config.getAdvisors().length == 0 && config.getTargetSource() == AdvisedSupport.EMPTY_TARGET_SOURCE) {
throw new AopConfigException("No advisors and no TargetSource specified");
}
// 整个构造过程非常无聊
// 简单提一下这里入参的config其实就是我们new然后一顿set的ProxyFactory
// ProxyFactory extends ProxyCreatorSupport
this.advised = config;
}
@Override
public Object getProxy(@Nullable ClassLoader classLoader) {
if (logger.isTraceEnabled()) {
logger.trace("Creating JDK dynamic proxy: " + this.advised.getTargetSource());
}
// 补全需要被代理的接口
Class<?>[] proxiedInterfaces = AopProxyUtils.completeProxiedInterfaces(this.advised, true);
findDefinedEqualsAndHashCodeMethods(proxiedInterfaces);
// step into ...
// 创建代理bean的实例
return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);
}
1.2 生成代理类的Class(defindClass)
该过程也解释了：为何JDK动态代理，只能是代理接口的实现类
// java.lang.reflect.Proxy#newProxyInstance
@CallerSensitive
public static Object newProxyInstance(ClassLoader loader,
Class<?>[] interfaces,
InvocationHandler h)
throws IllegalArgumentException
{
Objects.requireNonNull(h);
final Class<?>[] intfs = interfaces.clone();
final SecurityManager sm = System.getSecurityManager();
if (sm != null) {
checkProxyAccess(Reflection.getCallerClass(), loader, intfs);
}
// step into ...
// 这里有说法的 <- 为什么可以获取代理类的Class实例 <- classloader.defindClass <- 生成代理类的字节码
// 注意：这里把被代理类实现的所有接口传入
/*
* Look up or generate the designated proxy class.
*/
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);
}
}
// java.lang.reflect.Proxy#getProxyClass0
private static Class<?> getProxyClass0(ClassLoader loader,
Class<?>... interfaces) {
if (interfaces.length > 65535) {
throw new IllegalArgumentException("interface limit exceeded");
}
// step into ...
// 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
return proxyClassCache.get(loader, interfaces);
}
private final ReferenceQueue<K> refQueue
= new ReferenceQueue<>();
// the key type is Object for supporting null key
private final ConcurrentMap<Object, ConcurrentMap<Object, Supplier<V>>> map
= new ConcurrentHashMap<>();
private final BiFunction<K, P, ?> subKeyFactory;
private final BiFunction<K, P, V> valueFactory;
// java.lang.reflect.WeakCache#get
/**
* Look-up the value through the cache. This always evaluates the
* {@code subKeyFactory} function and optionally evaluates
* {@code valueFactory} function if there is no entry in the cache for given
* pair of (key, subKey) or the entry has already been cleared.
*
* @param key possibly null key
* @param parameter parameter used together with key to create sub-key and
* value (should not be null)
* @return the cached value (never null)
* @throws NullPointerException if {@code parameter} passed in or
* {@code sub-key} calculated by
* {@code subKeyFactory} or {@code value}
* calculated by {@code valueFactory} is null.
*/
public V get(K key, P parameter) {
Objects.requireNonNull(parameter);
expungeStaleEntries();
Object cacheKey = CacheKey.valueOf(key, refQueue);
// lazily install the 2nd level valuesMap for the particular cacheKey
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;
}
}
// create subKey and retrieve the possible Supplier<V> stored by that
// subKey from valuesMap
Object subKey = Objects.requireNonNull(subKeyFactory.apply(key, parameter));
Supplier<V> supplier = valuesMap.get(subKey);
Factory factory = null;
while (true) {
if (supplier != null) {
// step into ...
// supplier might be a Factory or a CacheValue<V> instance
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)) {
// supplier其实就是一个factory
// successfully replaced
// cleared CacheEntry / unsuccessful Factory
// with our Factory
supplier = factory;
} else {
// retry with current supplier
supplier = valuesMap.get(subKey);
}
}
}
}
// java.lang.reflect.WeakCache.Factory#get
@Override
public synchronized V get() { // serialize access
// re-check
Supplier<V> supplier = valuesMap.get(subKey);
if (supplier != this) {
// something changed while we were waiting:
// might be that we were replaced by a CacheValue
// or were removed because of failure ->
// return null to signal WeakCache.get() to retry
// the loop
return null;
}
// else still us (supplier == this)
// create new value
V value = null;
try {
// step into ...
value = Objects.requireNonNull(valueFactory.apply(key, parameter));
} finally {
if (value == null) { // remove us on failure
valuesMap.remove(subKey, this);
}
}
// the only path to reach here is with non-null value
assert value != null;
// wrap value with CacheValue (WeakReference)
CacheValue<V> cacheValue = new CacheValue<>(value);
// put into reverseMap
reverseMap.put(cacheValue, Boolean.TRUE);
// try replacing us with CacheValue (this should always succeed)
if (!valuesMap.replace(subKey, this, cacheValue)) {
throw new AssertionError("Should not reach here");
}
// successfully replaced us with new CacheValue -> return the value
// wrapped by it
return value;
}
// java.lang.reflect.Proxy.ProxyClassFactory#apply
@Override
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.
*/
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.
*/
if (!interfaceClass.isInterface()) {
throw new IllegalArgumentException(
interfaceClass.getName() + " is not an interface");
}
/*
* Verify that this interface is not a duplicate.
*/
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.
*/
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 + ".";
}
// 拼接代理类名
// com.sun.proxy.$Proxy49(自增数)
/*
* Choose a name for the proxy class to generate.
*/
long num = nextUniqueNumber.getAndIncrement();
String proxyName = proxyPkg + proxyClassNamePrefix + num;
// step into ...
// 这里返回代理类的字节码
/*
* Generate the specified proxy class.
*/
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());
}
}
// sun.misc.ProxyGenerator#generateProxyClass(java.lang.String, java.lang.Class<?>[], int)
public static byte[] generateProxyClass(final String var0, Class<?>[] var1, int var2) {
// step into ...
// 先得到代理类的构建器
ProxyGenerator var3 = new ProxyGenerator(var0, var1, var2);
// 开始一顿输出成字节数组
final byte[] var4 = var3.generateClassFile();
if (saveGeneratedFiles) {
AccessController.doPrivileged(new PrivilegedAction<Void>() {
public Void run() {
try {
int var1 = var0.lastIndexOf(46);
Path var2;
if (var1 > 0) {
Path var3 = Paths.get(var0.substring(0, var1).replace('.', File.separatorChar));
Files.createDirectories(var3);
var2 = var3.resolve(var0.substring(var1 + 1, var0.length()) + ".class");
} else {
var2 = Paths.get(var0 + ".class");
}
Files.write(var2, var4, new OpenOption[0]);
return null;
} catch (IOException var4x) {
throw new InternalError("I/O exception saving generated file: " + var4x);
}
}
});
}
return var4;
}
// sun.misc.ProxyGenerator#generateClassFile
private byte[] generateClassFile() {
// 将三个默认代理的方法加上
this.addProxyMethod(hashCodeMethod, Object.class);
this.addProxyMethod(equalsMethod, Object.class);
this.addProxyMethod(toStringMethod, Object.class);
// 获取代理类实现的接口
Class[] var1 = this.interfaces;
int var2 = var1.length;
int var3;
Class var4;
for(var3 = 0; var3 < var2; ++var3) {
var4 = var1[var3];
// 获取代理类实现接口的所有方法
Method[] var5 = var4.getMethods();
int var6 = var5.length;
for(int var7 = 0; var7 < var6; ++var7) {
Method var8 = var5[var7];
// step into ...
// 累加代理类实现接口的方法
this.addProxyMethod(var8, var4);
}
}
Iterator var11 = this.proxyMethods.values().iterator();
List var12;
while(var11.hasNext()) {
var12 = (List)var11.next();
checkReturnTypes(var12);
}
Iterator var15;
try {
this.methods.add(this.generateConstructor());
var11 = this.proxyMethods.values().iterator();
while(var11.hasNext()) {
var12 = (List)var11.next();
var15 = var12.iterator();
while(var15.hasNext()) {
ProxyGenerator.ProxyMethod var16 = (ProxyGenerator.ProxyMethod)var15.next();
this.fields.add(new ProxyGenerator.FieldInfo(var16.methodFieldName, "Ljava/lang/reflect/Method;", 10));
this.methods.add(var16.generateMethod());
}
}
this.methods.add(this.generateStaticInitializer());
} catch (IOException var10) {
throw new InternalError("unexpected I/O Exception", var10);
}
if (this.methods.size() > 65535) {
throw new IllegalArgumentException("method limit exceeded");
} else if (this.fields.size() > 65535) {
throw new IllegalArgumentException("field limit exceeded");
} else {
this.cp.getClass(dotToSlash(this.className));
this.cp.getClass("java/lang/reflect/Proxy");
var1 = this.interfaces;
var2 = var1.length;
for(var3 = 0; var3 < var2; ++var3) {
var4 = var1[var3];
this.cp.getClass(dotToSlash(var4.getName()));
}
this.cp.setReadOnly();
ByteArrayOutputStream var13 = new ByteArrayOutputStream();
DataOutputStream var14 = new DataOutputStream(var13);
try {
var14.writeInt(-889275714);
var14.writeShort(0);
var14.writeShort(49);
this.cp.write(var14);
var14.writeShort(this.accessFlags);
var14.writeShort(this.cp.getClass(dotToSlash(this.className)));
var14.writeShort(this.cp.getClass("java/lang/reflect/Proxy"));
var14.writeShort(this.interfaces.length);
Class[] var17 = this.interfaces;
int var18 = var17.length;
for(int var19 = 0; var19 < var18; ++var19) {
Class var22 = var17[var19];
var14.writeShort(this.cp.getClass(dotToSlash(var22.getName())));
}
var14.writeShort(this.fields.size());
var15 = this.fields.iterator();
// 一顿循环将接口的代理类的接口方法写入代理类构建器
while(var15.hasNext()) {
ProxyGenerator.FieldInfo var20 = (ProxyGenerator.FieldInfo)var15.next();
var20.write(var14);
}
var14.writeShort(this.methods.size());
var15 = this.methods.iterator();
F
while(var15.hasNext()) {
ProxyGenerator.MethodInfo var21 = (ProxyGenerator.MethodInfo)var15.next();
var21.write(var14);
}
var14.writeShort(0);
return var13.toByteArray();
} catch (IOException var9) {
throw new InternalError("unexpected I/O Exception", var9);
}
}
}
1.3 通过构造器反射创建代理类的实例
// java.lang.reflect.Proxy#newProxyInstance
@CallerSensitive
public static Object newProxyInstance(ClassLoader loader,
Class<?>[] interfaces,
InvocationHandler h)
throws IllegalArgumentException
{
Objects.requireNonNull(h);
final Class<?>[] intfs = interfaces.clone();
final SecurityManager sm = System.getSecurityManager();
if (sm != null) {
checkProxyAccess(Reflection.getCallerClass(), loader, intfs);
}
/*
* Look up or generate the designated proxy class.
*/
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;
}
});
}
// step into ...
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);
}
}
public T newInstance(Object ... initargs)
throws InstantiationException, IllegalAccessException,
IllegalArgumentException, InvocationTargetException
{
if (!override) {
if (!Reflection.quickCheckMemberAccess(clazz, modifiers)) {
Class<?> caller = Reflection.getCallerClass();
checkAccess(caller, clazz, null, modifiers);
}
}
if ((clazz.getModifiers() & Modifier.ENUM) != 0)
throw new IllegalArgumentException("Cannot reflectively create enum objects");
ConstructorAccessor ca = constructorAccessor; // read volatile
if (ca == null) {
ca = acquireConstructorAccessor();
}
// step into ...
@SuppressWarnings("unchecked")
T inst = (T) ca.newInstance(initargs);
return inst;
}
public Object newInstance(Object[] var1) throws InstantiationException, IllegalArgumentException, InvocationTargetException {
// step into ...
// 委派给native本地实现方法
return this.delegate.newInstance(var1);
}
public Object newInstance(Object[] var1) throws InstantiationException, IllegalArgumentException, InvocationTargetException {
if (++this.numInvocations > ReflectionFactory.inflationThreshold() && !ReflectUtil.isVMAnonymousClass(this.c.getDeclaringClass())) {
ConstructorAccessorImpl var2 = (ConstructorAccessorImpl)(new MethodAccessorGenerator()).generateConstructor(this.c.getDeclaringClass(), this.c.getParameterTypes(), this.c.getExceptionTypes(), this.c.getModifiers());
this.parent.setDelegate(var2);
}
// step into ...
return newInstance0(this.c, var1);
}
private static native Object newInstance0(Constructor<?> var0, Object[] var1) throws InstantiationException, IllegalArgumentException, InvocationTargetException;
2. 代理类实例在运行时的调用过程
@Override
public Object getProxy(@Nullable ClassLoader classLoader) {
if (logger.isTraceEnabled()) {
logger.trace("Creating JDK dynamic proxy: " + this.advised.getTargetSource());
}
Class<?>[] proxiedInterfaces = AopProxyUtils.completeProxiedInterfaces(this.advised, true);
findDefinedEqualsAndHashCodeMethods(proxiedInterfaces);
// step into ...
return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);
}
@CallerSensitive
public static Object newProxyInstance(ClassLoader loader,
Class<?>[] interfaces,
// step into ...
// 即传入的this已实现InvocationHandler接口
InvocationHandler h)
throws IllegalArgumentException
{
Objects.requireNonNull(h);
final Class<?>[] intfs = interfaces.clone();
final SecurityManager sm = System.getSecurityManager();
if (sm != null) {
checkProxyAccess(Reflection.getCallerClass(), loader, intfs);
}
/*
* Look up or generate the designated proxy class.
*/
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);
}
}
// org.springframework.aop.framework.JdkDynamicAopProxy#invoke
@Override
@Nullable
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
Object oldProxy = null;
boolean setProxyContext = false;
TargetSource targetSource = this.advised.targetSource;
Object target = null;
try {
if (!this.equalsDefined && AopUtils.isEqualsMethod(method)) {
// 代理equals()
// The target does not implement the equals(Object) method itself.
return equals(args[0]);
}
else if (!this.hashCodeDefined && AopUtils.isHashCodeMethod(method)) {
// 代理hashCode()
// The target does not implement the hashCode() method itself.
return hashCode();
}
else if (method.getDeclaringClass() == DecoratingProxy.class) {
// There is only getDecoratedClass() declared -> dispatch to proxy config.
return AopProxyUtils.ultimateTargetClass(this.advised);
}
else if (!this.advised.opaque && method.getDeclaringClass().isInterface() &&
method.getDeclaringClass().isAssignableFrom(Advised.class)) {
// Service invocations on ProxyConfig with the proxy config...
return AopUtils.invokeJoinpointUsingReflection(this.advised, method, args);
}
Object retVal;
// 如果设置了 exposeProxy，那么将 proxy 放到 ThreadLocal 中
if (this.advised.exposeProxy) {
// Make invocation available if necessary.
oldProxy = AopContext.setCurrentProxy(proxy);
setProxyContext = true;
}
// Get as late as possible to minimize the time we "own" the target,
// in case it comes from a pool.
target = targetSource.getTarget();
Class<?> targetClass = (target != null ? target.getClass() : null);
// 获取拦截器链(默认index:0为spring自带的ExposeInvocationInterceptor)
// Get the interception chain for this method.
List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);
// 空链不需要执行增强
// Check whether we have any advice. If we don't, we can fallback on direct
// reflective invocation of the target, and avoid creating a MethodInvocation.
if (chain.isEmpty()) {
// We can skip creating a MethodInvocation: just invoke the target directly
// Note that the final invoker must be an InvokerInterceptor so we know it does
// nothing but a reflective operation on the target, and no hot swapping or fancy proxying.
Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
retVal = AopUtils.invokeJoinpointUsingReflection(target, method, argsToUse);
}
else {
// chain拦截器链、真实方法均传入这个构造(里面仅仅是赋值属性而已)
// We need to create a method invocation...
MethodInvocation invocation =
new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain);
// 之后的递归调用参考 https://blog.csdn.net/weixin_43638238/article/details/126615336
// 从这里开始执行代理增强的方法(如果有拦截器链的话)
// 注释:在拦截器链中执行
// Proceed to the joinpoint through the interceptor chain.
retVal = invocation.proceed();
}
// Massage return value if necessary.
Class<?> returnType = method.getReturnType();
if (retVal != null && retVal == target &&
returnType != Object.class && returnType.isInstance(proxy) &&
!RawTargetAccess.class.isAssignableFrom(method.getDeclaringClass())) {
// Special case: it returned "this" and the return type of the method
// is type-compatible. Note that we can't help if the target sets
// a reference to itself in another returned object.
retVal = proxy;
}
else if (retVal == null && returnType != Void.TYPE && returnType.isPrimitive()) {
throw new AopInvocationException(
"Null return value from advice does not match primitive return type for: " + method);
}
return retVal;
}
finally {
if (target != null && !targetSource.isStatic()) {
// Must have come from TargetSource.
targetSource.releaseTarget(target);
}
if (setProxyContext) {
// Restore old proxy.
AopContext.setCurrentProxy(oldProxy);
}
}
}
3. jdk反射包下参与到代理的基类
此处的代理删减较多，详细代码可以参考上面的小节或者源码
- java.lang.reflect：依赖并对sun.reflect的一些组件做了相应的封装:Method、Construct等(存在对应关系)
- sun.reflect：包下的MethodAccessor、ConstructAccessor分别支撑了java反射方法调用、实例构造的能力
- sun.misc：对sun.reflect包下MethodAccessor、ConstructAccessor等组建的构建过程的一个封装
这里不按代理类创建、调用的顺序，而是采用基类所在包的顺序描述(强调关联性)
@CallerSensitive注解：这个注解是Java修复用的。防止使用者使用双重反射来提升权限，原理是因为当时反射只检查深度的调用者的类是否有权限，本身的类是没有这么高权限的，但是可以通过多重反射来提高调用的权限。
使用该注解，getCallerClass方法就会直接跳过有 @CallerSensitive修饰的接口方法，直接查找真实的调用者（actual caller）。
这段引用的出处
3.1 java.lang.reflect
3.1.1 Proxy：jdk暴露的创建代理对象的类
public class Proxy implements java.io.Serializable {
@CallerSensitive
public static Object newProxyInstance(ClassLoader loader,
Class<?>[] interfaces,
InvocationHandler h)
throws IllegalArgumentException
{
// 被代理类所实现的接口
final Class<?>[] intfs = interfaces.clone();
// 内部有一个cache
// 如果没有命中，将调用内部私有的ProxyClassFactory生成代理类的字节码并且defindClass
Class<?> cl = getProxyClass0(loader, intfs);
final Constructor<?> cons = cl.getConstructor(constructorParams);
final InvocationHandler ih = h;
// 这里可以看到JDK代理可以借助反射代理private方法
if (!Modifier.isPublic(cl.getModifiers())) {
AccessController.doPrivileged(new PrivilegedAction<Void>() {
public Void run() {
cons.setAccessible(true);
return null;
}
});
}
// 这个时候还是Constructor类型
return cons.newInstance(new Object[]{h});
}
private static final class ProxyClassFactory implements BiFunction<ClassLoader, Class<?>[], Class<?>>
{
// jdk代理类前缀
private static final String proxyClassNamePrefix = "$Proxy";
// 新增&唯一的代理类数字编号
private static final AtomicLong nextUniqueNumber = new AtomicLong();
@Override
public Class<?> apply(ClassLoader loader, Class<?>[] interfaces) {
// 代理类类名拼接规则
long num = nextUniqueNumber.getAndIncrement();
String proxyName = proxyPkg + proxyClassNamePrefix + num;
// 代理类字节码
byte[] proxyClassFile = ProxyGenerator.generateProxyClass(
proxyName, interfaces, accessFlags);
// 加载到内存
return defineClass0(loader, proxyName, proxyClassFile, 0, proxyClassFile.length);
}
}
private static native Class<?> defineClass0(ClassLoader loader, String name, byte[] b, int off, int len);
}
3.1.2 InvocationHandler：jdk暴露的代理方法的调用时钩子
public interface InvocationHandler {
public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable;
}
/* ------------ 这里插一段spring.aop借助这个接口参与到jdk代理类调用时的代码 ---------------*/
final class JdkDynamicAopProxy implements AopProxy, InvocationHandler, Serializable {
@Override
@Nullable
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
Object oldProxy = null;
boolean setProxyContext = false;
TargetSource targetSource = this.advised.targetSource;
Object target = null;
target = targetSource.getTarget();
Class<?> targetClass = (target != null ? target.getClass() : null);
// 获取用于增强被代理方法的所有advice
List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);
// 将拦截器的增强过程在这里执行
MethodInvocation invocation =
new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain);
// 这里使spring.aop的增强逻辑参与进来了
retVal = invocation.proceed();
Class<?> returnType = method.getReturnType();
return retVal;
}
}
3.1.3 Method & Construct
// Method -------------------------------
public final class Method extends Executable {
private Method root;
private volatile MethodAccessor methodAccessor;
@CallerSensitive
public Object invoke(Object obj, Object... args)
throws IllegalAccessException, IllegalArgumentException,
InvocationTargetException
{
MethodAccessor ma = methodAccessor; // read volatile
return ma.invoke(obj, args);
}
}
// Constructor -------------------------------
public final class Constructor<T> extends Executable {
@CallerSensitive
public T newInstance(Object ... initargs)
throws InstantiationException, IllegalAccessException,
IllegalArgumentException, InvocationTargetException
{
ConstructorAccessor ca = constructorAccessor; // read volatile
T inst = (T) ca.newInstance(initargs);
return inst;
}
}
3.2 sun.reflect
3.2.1 ConstructAccessor及其子类
public interface ConstructorAccessor {
Object newInstance(Object[] var1) throws InstantiationException, IllegalArgumentException, InvocationTargetException;
}
abstract class ConstructorAccessorImpl extends MagicAccessorImpl implements ConstructorAccessor {
Object newInstance(Object[] var1) throws InstantiationException, IllegalArgumentException, InvocationTargetException;
}
class DelegatingConstructorAccessorImpl extends ConstructorAccessorImpl {
// 持有 NativeConstructorAccessorImpl 的引用
private ConstructorAccessorImpl delegate;
public Object newInstance(Object[] var1) throws InstantiationException, IllegalArgumentException, InvocationTargetException {
return this.delegate.newInstance(var1);
}
}
class NativeConstructorAccessorImpl extends ConstructorAccessorImpl {
// 也持有 DelegatingConstructorAccessorImpl 的引用
private DelegatingConstructorAccessorImpl parent;
public Object newInstance(Object[] var1) throws InstantiationException, IllegalArgumentException, InvocationTargetException {
// Native版本一开始启动快，但是随着运行时间变长，速度变慢。Java版本一开始加载慢，但是随着运行时间变长，速度变快
// 正是因为两种存在这些问题，所以第一次加载时使用的是NativeMethodAccessorImpl
// 而当反射调用次数超过15次之后，则使用MethodAccessorGenerator生成的MethodAccessorImpl对象去实现反射。
if (++this.numInvocations > ReflectionFactory.inflationThreshold() && !ReflectUtil.isVMAnonymousClass(this.c.getDeclaringClass())) {
ConstructorAccessorImpl var2 = (ConstructorAccessorImpl)(new MethodAccessorGenerator()).generateConstructor(this.c.getDeclaringClass(), this.c.getParameterTypes(), this.c.getExceptionTypes(), this.c.getModifiers());
this.parent.setDelegate(var2);
}
return newInstance0(this.c, var1);
}
// 底层使用本地支持来创建代理类
private static native Object newInstance0(Constructor<?> var0, Object[] var1) throws InstantiationException, IllegalArgumentException, InvocationTargetException;
}
3.2.2 MethodAccessor及其子类
仔细看，跟ConstructAccessor差不多，这里就不解释了
public interface MethodAccessor {
Object invoke(Object var1, Object[] var2) throws IllegalArgumentException, InvocationTargetException;
}
class DelegatingMethodAccessorImpl extends MethodAccessorImpl {
private MethodAccessorImpl delegate;
public Object invoke(Object var1, Object[] var2) throws IllegalArgumentException, InvocationTargetException {
return this.delegate.invoke(var1, var2);
}
}
class NativeMethodAccessorImpl extends MethodAccessorImpl {
private final Method method;
private DelegatingMethodAccessorImpl parent;
public Object invoke(Object var1, Object[] var2) throws IllegalArgumentException, InvocationTargetException {
if (++this.numInvocations > ReflectionFactory.inflationThreshold() && !ReflectUtil.isVMAnonymousClass(this.method.getDeclaringClass())) {
MethodAccessorImpl var3 = (MethodAccessorImpl)(new MethodAccessorGenerator()).generateMethod(this.method.getDeclaringClass(), this.method.getName(), this.method.getParameterTypes(), this.method.getReturnType(), this.method.getExceptionTypes(), this.method.getModifiers());
this.parent.setDelegate(var3);
}
return invoke0(this.method, var1, var2);
}
private static native Object invoke0(Method var0, Object var1, Object[] var2);
}
3.2.3 ReflectionFactory
public MethodAccessor newMethodAccessor(Method var1) {
// 构造 NativeMethodAccessorImpl 、DelegatingMethodAccessorImpl 并使得持有对方的引用
NativeMethodAccessorImpl var2 = new NativeMethodAccessorImpl(var1);
DelegatingMethodAccessorImpl var3 = new DelegatingMethodAccessorImpl(var2);
var2.setParent(var3);
return var3;
}
public ConstructorAccessor newConstructorAccessor(Constructor<?> var1) {
NativeConstructorAccessorImpl var3 = new NativeConstructorAccessorImpl(var1);
DelegatingConstructorAccessorImpl var4 = new DelegatingConstructorAccessorImpl(var3);
var3.setParent(var4);
return var4;
}
3.3 sun.misc
写出生成好的代理类字节码文件
public class ProxyGenerator {
public static byte[] generateProxyClass(final String var0, Class<?>[] var1, int var2) {
ProxyGenerator var3 = new ProxyGenerator(var0, var1, var2);
final byte[] var4 = var3.generateClassFile();
if (saveGeneratedFiles) {
AccessController.doPrivileged(new PrivilegedAction<Void>() {
public Void run() {
Files.write(var2, var4, new OpenOption[0]);
}
});
}
return var4;
}
}
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