JDK1.8 动态代理机制及源码解析

Posted 2022-05-22 ly570

动态代理

a) jdk 动态代理 Proxy，
核心思想：通过实现被代理类的所有接口，生成一个字节码文件后构造一个代理对象，通过持有反射构造被代理类的一个实例，再通过invoke反射调用被代理类实例的方法，来实现代理。
缺点：被代理类必须实现一个或多个接口
参考链接：http://rejoy.iteye.com/blog/1627405
源码解析：见第四部分

cglib 动态代理

核心思想：通过生成子类字节码实现，代理类为每个委托方法都生成两个方法，以add方法为例，一个是重写的add方法，一个是CGLIB$add$0方法，该方法直接调用委托类的add方法；
底层：使用一个小而快的字节码处理框架ASM(Java字节码操控框架)，来转换字节码并生成新的类
缺点：不能代理final修饰的类，
参考链接：http://blog.csdn.net/yakoo5/article/details/9099133/
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AOP实现机制

a. 实现方式：cglib 和 jdk自带的Proxy实现
b. 策略：
1）如果是有接口声明的类进行AOP 时，spring调用的是Java.lang.reflection.Proxy 类来做处理
2）如果是没有接口声明的类时， spring通过cglib包和内部类来实现
c.配置：
<aop:aspectj-autoproxy proxy-target-class="true" />配置了这句话的话就会强制使用cglib代理。 默认就是false
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JDK动态代理Demo

//业务类接口
public interface MyBusinessInterface
public void processBusiness();

//业务实现类
public class MyBusinessInterfaceImpl implements MyBusinessInterface
public void processBusiness()
System.out.println("processing business.....");

//被代理对象调用处理程序，必须实现InvocationHandler接口
public class MyInvocationHandler implements InvocationHandler
//所代理的真实对象
private Object target = null;
//构造器，用于传入所代理的真实对象
MyInvocationHandler(Object target)
this.target = target;

//需要我们实现具体业务的地方
//proxy:　　所生成代理类实例
//method:　　指代的是我们所要调用真实对象的某个方法的Method对象
//args:　　指代的是调用真实对象某个方法时接受的参数
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable
System.out.println("You can do something here before process your business");
//调用目标对象的方法
Object result = method.invoke(target, args);
System.out.println("You can do something here after process your business");
//返回处理结果
return result;

//测试用例
public class Test

public static void main(String[] args)
//被代理真实对象
MyBusinessInterfaceImpl bpimpl = new MyBusinessInterfaceImpl();
//被代理对象调用处理程序，需传入被代理对象
MyInvocationHandler handler = new MyInvocationHandler(bpimpl);
//生成代理类实例
MyBusinessInterface bp = (MyBusinessInterface)Proxy.newProxyInstance(bpimpl.getClass().getClassLoader(), bpimpl.getClass().getInterfaces(), handler);
//调用processBusiness
bp.processBusiness();


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JDK1.8动态代理源码解析

Proxy解析

 

//代理类
public class Proxy implements java.io.Serializable

private static final long serialVersionUID = -2222568056686623797L;

//代理类构造函数的参数类型
private static final Class<?>[] constructorParams =
InvocationHandler.class ;

//代理类缓存
private static final WeakCache<ClassLoader, Class<?>[], Class<?>>
proxyClassCache = new WeakCache<>(new KeyFactory(), new ProxyClassFactory());

//此代理实例的调用处理程序。
protected InvocationHandler h;

private Proxy()

//代理类构造函数，参数类型：constructorParams所指定
protected Proxy(InvocationHandler h)
Objects.requireNonNull(h);
this.h = h;

//获取目标代理类Class对象，需传入类加载器loader对象和被代理类实现接口数组interfaces随想
@CallerSensitive
public static Class<?> getProxyClass(ClassLoader loader,Class<?>... interfaces)
throws IllegalArgumentException
//拷贝接口数组
final Class<?>[] intfs = interfaces.clone();
final SecurityManager sm = System.getSecurityManager();
if (sm != null)
//校验代理类的访问问权限
checkProxyAccess(Reflection.getCallerClass(), loader, intfs);

//获取代理类Class对象
return getProxyClass0(loader, intfs);

//校验代理类的访问问权限,这一块比较底层，我也不明白
private static void checkProxyAccess(Class<?> caller, ClassLoader loader, Class<?>... interfaces)
SecurityManager sm = System.getSecurityManager();
if (sm != null)
//获取调用者类的类加载器
ClassLoader ccl = caller.getClassLoader();
if (VM.isSystemDomainLoader(loader) && !VM.isSystemDomainLoader(ccl))
sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);

ReflectUtil.checkProxyPackageAccess(ccl, interfaces);


//获取代理类的Clas对象
private static Class<?> getProxyClass0(ClassLoader loader,
Class<?>... interfaces)
if (interfaces.length > 65535)
throw new IllegalArgumentException("interface limit exceeded");

//如果存在给定接口的给定装入器定义的代理类存在，则只返回缓存的副本；
//否则，它将通过proxyclassfactory创建代理类
//jdk1.8后收敛到这里 生成代理类字节码过程: ProxyClassFactory中了
return proxyClassCache.get(loader, interfaces);

//用于带有0个实现接口的代理类的key键值
private static final Object key0 = new Object();

/*
* Key1 and Key2 are optimized for the common use of dynamic proxies
* that implement 1 or 2 interfaces.
*/

/*
* a key used for proxy class with 1 implemented interface
*/
//用于带有1个实现接口的代理类的key键值
private static final class Key1 extends WeakReference<Class<?>>
private final int hash;

Key1(Class<?> intf)
super(intf);
this.hash = intf.hashCode();

@Override
public int hashCode()
return hash;

@Override
public boolean equals(Object obj)
Class<?> intf;
return this == obj ||
obj != null &&
obj.getClass() == Key1.class &&
(intf = get()) != null &&
intf == ((Key1) obj).get();

// //用于带有2个实现接口的代理类的key键值
private static final class Key2 extends WeakReference<Class<?>>
private final int hash;
//弱引用对象：存放第二个接口类对象
private final WeakReference<Class<?>> ref2;

Key2(Class<?> intf1, Class<?> intf2)
super(intf1);
hash = 31 * intf1.hashCode() + intf2.hashCode();
ref2 = new WeakReference<Class<?>>(intf2);

@Override
public int hashCode()
return hash;

@Override
public boolean equals(Object obj)
Class<?> intf1, intf2;
return this == obj ||
obj != null &&
obj.getClass() == Key2.class &&
(intf1 = get()) != null &&
intf1 == ((Key2) obj).get() &&
(intf2 = ref2.get()) != null &&
intf2 == ((Key2) obj).ref2.get();

// 这里用于带有>=3个实现接口的代理类的key键值（可以当实现任意数目接口的代理的key）
private static final class KeyX
//接口数组对象的hash值
private final int hash;
//弱引用对象数组：存放表示接口的类对象数组
private final WeakReference<Class<?>>[] refs;

@SuppressWarnings("unchecked")
KeyX(Class<?>[] interfaces)
hash = Arrays.hashCode(interfaces);
//构造一个弱引用对象数组
refs = (WeakReference<Class<?>>[])new WeakReference<?>[interfaces.length];
for (int i = 0; i < interfaces.length; i++)
refs[i] = new WeakReference<>(interfaces[i]);

@Override
public int hashCode()
return hash;

@Override
public boolean equals(Object obj)
return this == obj ||
obj != null &&
obj.getClass() == KeyX.class &&
equals(refs, ((KeyX) obj).refs);

private static boolean equals(WeakReference<Class<?>>[] refs1,
WeakReference<Class<?>>[] refs2)
//长度是否相等
if (refs1.length != refs2.length)
return false;

//弱引用对象数组内接口类是否相同
for (int i = 0; i < refs1.length; i++)
Class<?> intf = refs1[i].get();
if (intf == null || intf != refs2[i].get())
return false;


return true;

//将接口数组映射到一个最佳键的函数，其中表示接口的类对象为弱引用。
private static final class KeyFactory
implements BiFunction<ClassLoader, Class<?>[], Object>

@Override
public Object apply(ClassLoader classLoader, Class<?>[] interfaces)
switch (interfaces.length)
case 1: return new Key1(interfaces[0]); // the most frequent
case 2: return new Key2(interfaces[0], interfaces[1]);
case 0: return key0;
default: return new KeyX(interfaces);

//一个工厂函数生成‘给定类装载器和接口数组的代理类’。
private static final class ProxyClassFactory
implements BiFunction<ClassLoader, Class<?>[], Class<?>>

//所有代理类名称的前缀
private static final String proxyClassNamePrefix = "$Proxy";

//用于生成唯一代理类名称的下一个数字
private static final AtomicLong nextUniqueNumber = new AtomicLong();

@Override
public Class<?> apply(ClassLoader loader, Class<?>[] interfaces)

Map<Class<?>, Boolean> interfaceSet = new IdentityHashMap<>(interfaces.length);
for (Class<?> intf : interfaces)

//验证intf接口类Class对象是否为给定的classloder解析的
Class<?> interfaceClass = null;
try
//指定类加载器获取接口类class对象，
interfaceClass = Class.forName(intf.getName(), false, loader);
catch (ClassNotFoundException e)

//验证是否为同一个接口类对象，
if (interfaceClass != intf)
throw new IllegalArgumentException(
intf + " is not visible from class loader");

//验证类对象是否为接口
if (!interfaceClass.isInterface())
throw new IllegalArgumentException(
interfaceClass.getName() + " is not an interface");

/*
* Verify that this interface is not a duplicate.
* 验证此接口不是副本。
*/
if (interfaceSet.put(interfaceClass, Boolean.TRUE) != null)
throw new IllegalArgumentException(
"repeated interface: " + interfaceClass.getName());


//定义代理类的包
String proxyPkg = null;
//定义代理类的修饰符：public和final类型
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.
* 记录一个非公共代理接口的包，以便在同一个包中定义代理类。验证所有非公共代理接口都在同一个包中。
*/
for (Class<?> intf : interfaces)
//获取修饰符
int flags = intf.getModifiers();
if (!Modifier.isPublic(flags)) //不是public修饰符
//则定义代理类的修饰符符：final
accessFlags = Modifier.FINAL;
//获取接口类名称，如：com.text.MyInterface
String name = intf.getName();
int n = name.lastIndexOf(‘.‘);
//获取包名，如：com.text
String pkg = ((n == -1) ? "" : name.substring(0, n + 1));
if (proxyPkg == null)
//获取包名称
proxyPkg = pkg;
else if (!pkg.equals(proxyPkg)) //interfaces含有来自不同包的非公共接口,抛错
throw new IllegalArgumentException(
"non-public interfaces from different packages");

if (proxyPkg == null)
//如果没有非公开的代理接口，使用com.sun.proxy作为包名称
proxyPkg = ReflectUtil.PROXY_PACKAGE + ".";

//选择要生成的代理类的名称。
long num = nextUniqueNumber.getAndIncrement();
String proxyName = proxyPkg + proxyClassNamePrefix + num;

//真正生成指定的代理类字节码的地方
byte[] proxyClassFile = ProxyGenerator.generateProxyClass(
proxyName, interfaces, accessFlags);
try
//生成Calss对象
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());

//生成代理类对象
@CallerSensitive
public static Object newProxyInstance(ClassLoader loader,Class<?>[] interfaces,InvocationHandler h)
throws IllegalArgumentException
//调用处理程序不能为空
Objects.requireNonNull(h);
//拷贝接口数组对象
final Class<?>[] intfs = interfaces.clone();
final SecurityManager sm = System.getSecurityManager();
if (sm != null)
checkProxyAccess(Reflection.getCallerClass(), loader, intfs);

//查找或生成指定的代理类。
Class<?> cl = getProxyClass0(loader, intfs);

/*
* Invoke its constructor with the designated invocation handler.
* 调用指定的调用处理程序的构造函数
*/
try
if (sm != null)
//校验新代理类的权限
checkNewProxyPermission(Reflection.getCallerClass(), cl);

//获取代理类构造函数，参数类型必须为InvocationHandler
final Constructor<?> cons = cl.getConstructor(constructorParams);
final InvocationHandler ih = h;
//构造函数不是public，则设置当前构造函数为访问权限
if (!Modifier.isPublic(cl.getModifiers()))
AccessController.doPrivileged(new PrivilegedAction<Void>()
public Void run()
cons.setAccessible(true);
return null;

);

//调用构造函数构造代理类实例，入参数为‘调用处理程序’的实例,看到这里应该就明白jdk怎么实现动态代理的吧！
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);

private static void checkNewProxyPermission(Class<?> caller, Class<?> proxyClass)
SecurityManager sm = System.getSecurityManager();
if (sm != null)
if (ReflectUtil.isNonPublicProxyClass(proxyClass))
//调用者类加载器
ClassLoader ccl = caller.getClassLoader();
//代理类的类加载器
ClassLoader pcl = proxyClass.getClassLoader();

// do permission check if the caller is in a different runtime package
// of the proxy class
//获取代理类的包名
int n = proxyClass.getName().lastIndexOf(‘.‘);
String pkg = (n == -1) ? "" : proxyClass.getName().substring(0, n);
//获取调用者包名
n = caller.getName().lastIndexOf(‘.‘);
String callerPkg = (n == -1) ? "" : caller.getName().substring(0, n);
//类加载不相同或包名不相同，校验权限
if (pcl != ccl || !pkg.equals(callerPkg))
sm.checkPermission(new ReflectPermission("newProxyInPackage." + pkg));

public static boolean isProxyClass(Class<?> cl)
return Proxy.class.isAssignableFrom(cl) && proxyClassCache.containsValue(cl);

@CallerSensitive
public static InvocationHandler getInvocationHandler(Object proxy)
throws IllegalArgumentException

//验证该对象实际上是否为上一个代理实例。
if (!isProxyClass(proxy.getClass()))
throw new IllegalArgumentException("not a proxy instance");

final Proxy p = (Proxy) proxy;
final InvocationHandler ih = p.h;
if (System.getSecurityManager() != null)
Class<?> ihClass = ih.getClass();
Class<?> caller = Reflection.getCallerClass();
if (ReflectUtil.needsPackageAccessCheck(caller.getClassLoader(),
ihClass.getClassLoader()))

ReflectUtil.checkPackageAccess(ihClass);

return ih;

private static native Class<?> defineClass0(ClassLoader loader, String name,
byte[] b, int off, int len);

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WeakCache类解析 ####

 

//用处存放
final class WeakCache<K, P, V>

private final ReferenceQueue<K> refQueue = new ReferenceQueue<>();
// the key type is Object for supporting null key
//Map<类加载器，Map<接口数组对象key，代理类工厂Factory或代理类包装对象LookupValue>
private final ConcurrentMap<Object, ConcurrentMap<Object, Supplier<V>>> map = new ConcurrentHashMap<>();
//存放当前key所对应的实例是否已经生成
private final ConcurrentMap<Supplier<V>, Boolean> reverseMap = new ConcurrentHashMap<>();
//生成key的工厂（对应上面的Key1-X类）
private final BiFunction<K, P, ?> subKeyFactory;
//生成value（代理类工厂，对应上面的ProxyClassFactory类）
private final BiFunction<K, P, V> valueFactory;

//构造方法,指定key和value工厂
public WeakCache(BiFunction<K, P, ?> subKeyFactory,
BiFunction<K, P, V> valueFactory)
this.subKeyFactory = Objects.requireNonNull(subKeyFactory);
this.valueFactory = Objects.requireNonNull(valueFactory);

//获取缓存值，
public V get(K key, P parameter)
//parameter不能weinull
Objects.requireNonNull(parameter);
//删除老节点
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)
//添加cacheKey - ConcurrentMap<Object, Supplier<V>对象到map中
ConcurrentMap<Object, Supplier<V>> oldValuesMap = map.putIfAbsent(cacheKey,valuesMap = new ConcurrentHashMap<>());
if (oldValuesMap != null)
valuesMap = oldValuesMap;

//利用subKeyFactory生成subKey
Object subKey = Objects.requireNonNull(subKeyFactory.apply(key, parameter));
//获取valuesMap中subKey所对应的值，此时为cachevalue <V>实例（步骤1：cachevalue <V>实例的来源）
Supplier<V> supplier = valuesMap.get(subKey);
Factory factory = null;

while (true)
if (supplier != null)
//步骤1：supplier可能是一个工厂对象或一个cachevalue <V>实例
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)
//构造一个工厂对象(步骤1：工厂对象的来源）
factory = new Factory(key, parameter, subKey, valuesMap);

//
if (supplier == null)
//factory添加在valuesMap中
supplier = valuesMap.putIfAbsent(subKey, factory);
if (supplier == null)
// 添加成功，则factory赋值给supplier，此时supplier为一个工厂对象
supplier = factory;

// else retry with winning supplier
//失败则重试
else
//将valuesMap中subKey所对应的值替换为factory
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);

/**
* Checks whether the specified non-null value is already present in this
* @code WeakCache. The check is made using identity comparison regardless
* of whether value‘s class overrides @link Object#equals or not.
*
* @param value the non-null value to check
* @return true if given @code value is already cached
* @throws NullPointerException if value is null
*/
public boolean containsValue(V value)
Objects.requireNonNull(value);

expungeStaleEntries();
return reverseMap.containsKey(new LookupValue<>(value));

/**
* Returns the current number of cached entries that
* can decrease over time when keys/values are GC-ed.
*/
public int size()
expungeStaleEntries();
return reverseMap.size();

private void expungeStaleEntries()
CacheKey<K> cacheKey;
while ((cacheKey = (CacheKey<K>)refQueue.poll()) != null)
cacheKey.expungeFrom(map, reverseMap);

/**
* A factory @link Supplier that implements the lazy synchronized
* construction of the value and installment of it into the cache.
*/
private final class Factory implements Supplier<V>

private final K key;
private final P parameter;
private final Object subKey;
private final ConcurrentMap<Object, Supplier<V>> valuesMap;

Factory(K key, P parameter, Object subKey,
ConcurrentMap<Object, Supplier<V>> valuesMap)
this.key = key;
this.parameter = parameter;
this.subKey = subKey;
this.valuesMap = valuesMap;

@Override
public synchronized V get() // serialize access
//校验是否为同一个
Supplier<V> supplier = valuesMap.get(subKey);
if (supplier != this)
//在我们等待的时候，可能某些值已经被替换或则删除，返回null让WeakCache.get()再次循环获取
return null;

//创建一个新值
V value = null;
try
//调用valueFactory的applay方法生成一个新值
value = Objects.requireNonNull(valueFactory.apply(key, parameter));
finally
if (value == null) //如果生成失败，从valuesMap中删除值
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);

//尝试更换我们cachevalue（这应该总是成功的)此时
if (valuesMap.replace(subKey, this, cacheValue))
// 放在reversemap
reverseMap.put(cacheValue, Boolean.TRUE);
else
throw new AssertionError("Should not reach here");

//成功取代当前工厂对象为一个新的CacheValue（包裹着我们的需要对象：代理类）
return value;

//Value接口
private interface Value<V> extends Supplier<V>

//值对象：包裹着我们的需要对象：代理类
private static final class LookupValue<V> implements Value<V>
private final V value;

LookupValue(V value)
this.value = value;

@Override
public V get()
return value;

@Override
public int hashCode()
return System.identityHashCode(value); // compare by identity

@Override
public boolean equals(Object obj)
return obj == this ||
obj instanceof Value &&
this.value == ((Value<?>) obj).get(); // compare by identity

/**
* A @link Value that weakly references the referent.
*/
private static final class CacheValue<V>
extends WeakReference<V> implements Value<V>

private final int hash;

CacheValue(V value)
super(value);
this.hash = System.identityHashCode(value); // compare by identity

@Override
public int hashCode()
return hash;

@Override
public boolean equals(Object obj)
V value;
return obj == this ||
obj instanceof Value &&
// cleared CacheValue is only equal to itself
(value = get()) != null &&
value == ((Value<?>) obj).get(); // compare by identity

private static final class CacheKey<K> extends WeakReference<K>

// a replacement for null keys
private static final Object NULL_KEY = new Object();

static <K> Object valueOf(K key, ReferenceQueue<K> refQueue)
return key == null
// null key means we can‘t weakly reference it,
// so we use a NULL_KEY singleton as cache key
? NULL_KEY
// non-null key requires wrapping with a WeakReference
: new CacheKey<>(key, refQueue);

private final int hash;

private CacheKey(K key, ReferenceQueue<K> refQueue)
super(key, refQueue);
this.hash = System.identityHashCode(key); // compare by identity

@Override
public int hashCode()
return hash;

@Override
public boolean equals(Object obj)
K key;
return obj == this ||
obj != null &&
obj.getClass() == this.getClass() &&
// cleared CacheKey is only equal to itself
(key = this.get()) != null &&
// compare key by identity
key == ((CacheKey<K>) obj).get();

void expungeFrom(ConcurrentMap<?, ? extends ConcurrentMap<?, ?>> map,
ConcurrentMap<?, Boolean> reverseMap)
// removing just by key is always safe here because after a CacheKey
// is cleared and enqueue-ed it is only equal to itself
// (see equals method)...
ConcurrentMap<?, ?> valuesMap = map.remove(this);
// remove also from reverseMap if needed
if (valuesMap != null)
for (Object cacheValue : valuesMap.values())
reverseMap.remove(cacheValue);





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Proxy实际生成的代理类

import dynamic.proxy.UserService;
import java.lang.reflect.*;

public final class $Proxy11 extends Proxy
implements UserService

// 构造方法，参数就是刚才传过来的MyInvocationHandler类的实例
public $Proxy11(InvocationHandler invocationhandler)

super(invocationhandler);

public final boolean equals(Object obj)

try

return ((Boolean)super.h.invoke(this, m1, new Object[]
obj
)).booleanValue();

catch(Error _ex)
catch(Throwable throwable)

throw new UndeclaredThrowableException(throwable);

/**
* 这个方法是关键部分
*/
public final void add()

try

// 实际上就是调用MyInvocationHandler的public Object invoke(Object proxy, Method method, Object[] args)方法，第二个问题就解决了
super.h.invoke(this, m3, null);
return;

catch(Error _ex)
catch(Throwable throwable)

throw new UndeclaredThrowableException(throwable);

public final int hashCode()

try

return ((Integer)super.h.invoke(this, m0, null)).intValue();

catch(Error _ex)
catch(Throwable throwable)

throw new UndeclaredThrowableException(throwable);

public final String toString()

try

return (String)super.h.invoke(this, m2, null);

catch(Error _ex)
catch(Throwable throwable)

throw new UndeclaredThrowableException(throwable);

private static Method m1;
private static Method m3;
private static Method m0;
private static Method m2;

// 在静态代码块中获取了4个方法：Object中的equals方法、UserService中的add方法、Object中的hashCode方法、Object中toString方法
static

try

m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[]
Class.forName("java.lang.Object")
);
m3 = Class.forName("dynamic.proxy.UserService").getMethod("add", new Class[0]);
m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);
m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);

catch(NoSuchMethodException nosuchmethodexception)

throw new NoSuchMethodError(nosuchmethodexception.getMessage());

catch(ClassNotFoundException classnotfoundexception)

throw new NoClassDefFoundError(classnotfoundexception.getMessage());



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