一:經常使用的java代理模式
通常常常作java開發的知道java的代理模式一共有三種，第一種也就是靜態代理，這種用法比較簡單，沒有什麼魔法棒，比較好理解，另外兩種分別是JDK代理和cglib代理，他們分別是對接口代理和對class類自己進行代理，jdk代理要求類必須實現有一個或者多個接口，對接口進行字節碼加強在內存中實現新的class類去反射調用用戶target的實現類，這裏須要說明的是不論是cglic代理也好仍是jdk代理他們在內存中都要佔據方法區資源(jdk8 叫原空間)，從而達到代理目的，而cglib代理是對class類自己進行字節碼加強配合fastclass來實現代理，關於更多的cglib和jdk代理相關的內容你們能夠google搜索一下，網上有不少這裏不作再多的說明。下面咱們摒棄jdk，和cglib的複雜源碼來本身實現一個代理模式，來更深入的瞭解一下代理到底是怎麼造成的。html
二:java原生jdk代理demo和源碼分析
代理模式是指給某一個對象提供一個代理對象，並由代理對象控制對原對象的引用。通俗的來說代理模式就是咱們生活中常見的中介。這種模式有什麼用呢？它能夠在原對象的基礎上加強原對象的功能，好比在原對象調用一個方法的先後進行日誌、事務操做等。Spring AOP就使用了代理模式。如何實現代理模式呢？首先來看靜態代理。靜態代理是指在程序運行前就已經存在的編譯好的代理類是爲靜態代理。實現靜態代理有四個步驟：
①定義業務接口；
②被代理類實現業務接口；
③定義代理類並實現業務接口；
④最後即可經過客戶端進行調用。（這裏能夠理解成程序的main方法裏的內容）
咱們按照這個步驟去實現靜態代理。需求：在向數據庫添加一個用戶時先後打印日誌。
②被代理類實現業務接口；
③定義代理類並實現業務接口；
④最後即可經過客戶端進行調用。（這裏能夠理解成程序的main方法裏的內容）
咱們按照這個步驟去實現靜態代理。需求：在向數據庫添加一個用戶時先後打印日誌。
JDK DEMO示例
IUserService.java
public interface IUserService {
void add(String name);
}
UserServiceImpl.java java
public class UserServiceImpl implements IUserService{
@Override
public void add(String name) {
System.out.println("數據庫中插入： "+name+" 的用戶");
}
}
MyInvocationHandler.javaspring
public class MyInvocationHandler implements InvocationHandler {
//被代理對象，Object類型
private Object target;
public MyInvocationHandler(Object target) {
this.target = target;
}
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
System.out.println("準備向數據庫中插入數據");
Object returnvalue = method.invoke(target, args);
System.out.println("插入數據庫成功");
return returnvalue;
}
}
測試類數據庫
public static void main(String[] args) {
IUserService target = new UserServiceImpl();
MyInvocationHandler handler = new MyInvocationHandler(target);
IUserService proxyObject = (IUserService) Proxy.newProxyInstance(DynamicProxyTest.class.getClassLoader(),
target.getClass().getInterfaces(), handler);
proxyObject.add("張玉龍");
}
使用上很是簡單、網上demo也不少，不作充分講解，對jdk代理用法的小夥伴若是還不熟悉這塊代碼，就先了解一下jdk代理的使用方式，而後在回來繼續看下面的源碼分析數組
JDK代理源碼深度分析
這部分若是想要更快更好的理解，建議一邊對着源碼(本文JDK 1.8)，一邊看着博客。畢竟本身親身實踐效果纔好嘛。
Proxy.newProxyInstance( ClassLoaderloader, Class[] interfaces, InvocationHandler h)
產生了代理對象，因此咱們進到
newProxyInstance
的實現：
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;
}
});
}
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);
}
}
這段代碼核心就是經過
getProxyClass0(loader, intfs)獲得代理類的Class對象，而後經過Class對象獲得構造方法，進而建立代理對象。下一步看
getProxyClass0這個方法。
//此方法也是Proxy類下的方法
private static Class<?> getProxyClass0(ClassLoader loader,
Class<?>... interfaces) {
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
//意思是：若是代理類被指定的類加載器loader定義了，並實現了給定的接口interfaces，
//那麼就返回緩存的代理類對象，不然使用ProxyClassFactory建立代理類。
return proxyClassCache.get(loader, interfaces);
}
這裏看到proxyClassCache，有Cache便知道是緩存的意思，正好呼應了前面Look up or generate the designated proxy class。查詢（在緩存中已經有）或生成指定的代理類的class對象這段註釋。緩存
proxyClassCache是個WeakCache類的對象，調用proxyClassCache.get(loader, interfaces); 能夠獲得緩存的代理類或建立代理類（沒有緩存的狀況）。說明WeakCache中有
get這個方法。先看下WeakCache類的定義（這裏先只給出變量的定義和構造函數）：
//K表明key的類型，P表明參數的類型，V表明value的類型。
// WeakCache<ClassLoader, Class<?>[], Class<?>> proxyClassCache 說明proxyClassCache存的值是Class<?>對象，正是咱們須要的代理類對象。
final class WeakCache<K, P, V> {
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 ConcurrentMap<Supplier<V>, Boolean> reverseMap
= new ConcurrentHashMap<>();
private final BiFunction<K, P, ?> subKeyFactory;
private final BiFunction<K, P, V> valueFactory;
public WeakCache(BiFunction<K, P, ?> subKeyFactory,
BiFunction<K, P, V> valueFactory) {
this.subKeyFactory = Objects.requireNonNull(subKeyFactory);
this.valueFactory = Objects.requireNonNull(valueFactory);
}
其中map變量是實現緩存的核心變量，他是一個雙重的Map結構:
(key, sub-key) -> value。其中key是傳進來的Classloader進行包裝後的對象，sub-key是由WeakCache構造函數傳人的
KeyFactory()生成的。value就是產生代理類的對象，是由WeakCache構造函數傳人的
ProxyClassFactory()生成的
好，大致上說完WeakCache這個類的做用，咱們回到剛纔
proxyClassCache.get(loader, interfaces);這句代碼。get是WeakCache裏的方法。源碼以下
//K和P就是WeakCache定義中的泛型，key是類加載器，parameter是接口類數組
public V get(K key, P parameter) {
//檢查parameter不爲空
Objects.requireNonNull(parameter);
//清除無效的緩存
expungeStaleEntries();
// cacheKey就是(key, sub-key) -> value裏的一級key，
Object cacheKey = CacheKey.valueOf(key, refQueue);
// lazily install the 2nd level valuesMap for the particular cacheKey
//根據一級key獲得 ConcurrentMap<Object, Supplier<V>>對象。若是以前不存在，則新建一個ConcurrentMap<Object, Supplier<V>>和cacheKey（一級key）一塊兒放到map中。
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
//這部分就是調用生成sub-key的代碼，上面咱們已經看過怎麼生成的了
Object subKey = Objects.requireNonNull(subKeyFactory.apply(key, parameter));
//經過sub-key獲得supplier
Supplier<V> supplier = valuesMap.get(subKey);
//supplier實際上就是這個factory
Factory factory = null;
while (true) {
//若是緩存裏有supplier ，那就直接經過get方法，獲得代理類對象，返回，就結束了，一下子分析get方法。
if (supplier != null) {
// 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
//下面的全部代碼目的就是：若是緩存中沒有supplier，則建立一個Factory對象，把factory對象在多線程的環境下安全的賦給supplier。
//由於是在while（true）中，賦值成功後又回到上面去調get方法，返回才結束。
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);
}
}
}
}
因此接下來咱們看Factory類中的get方法。安全
public synchronized V get() { // serialize access
// re-check
Supplier<V> supplier = valuesMap.get(subKey);
//從新檢查獲得的supplier是否是當前對象
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 {
//代理類就是在這個位置調用valueFactory生成的
//valueFactory就是咱們傳入的 new ProxyClassFactory()
//一會咱們分析ProxyClassFactory()的apply方法
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)
//把value包裝成弱引用
CacheValue<V> cacheValue = new CacheValue<>(value);
// put into reverseMap
// reverseMap是用來實現緩存的有效性
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;
}
}
撥雲見日，來到ProxyClassFactory的apply方法，代理類就是在這裏生成的。多線程
//這裏的BiFunction<T, U, R>是個函數式接口，能夠理解爲用T，U兩種類型作參數，獲得R類型的返回值
private static final class ProxyClassFactory
implements BiFunction<ClassLoader, Class<?>[], Class<?>>
{
// prefix for all proxy class names
//全部代理類名字的前綴
private static final String proxyClassNamePrefix = "$Proxy";
// next number to use for generation of unique proxy class names
//用於生成代理類名字的計數器
private static final AtomicLong nextUniqueNumber = new AtomicLong();
@Override
public Class<?> apply(ClassLoader loader, Class<?>[] interfaces) {
Map<Class<?>, Boolean> interfaceSet = new IdentityHashMap<>(interfaces.length);
//驗證代理接口，可不看
for (Class<?> intf : interfaces) {
/*
* Verify that the class loader resolves the name of this
* interface to the same Class object.
*/
Class<?> interfaceClass = null;
try {
interfaceClass = Class.forName(intf.getName(), false, loader);
} catch (ClassNotFoundException e) {
}
if (interfaceClass != intf) {
throw new IllegalArgumentException(
intf + " is not visible from class loader");
}
/*
* Verify that the Class object actually represents an
* interface.
*/
if (!interfaceClass.isInterface()) {
throw new IllegalArgumentException(
interfaceClass.getName() + " is not an interface");
}
/*
* Verify that this interface is not a duplicate.
*/
if (interfaceSet.put(interfaceClass, Boolean.TRUE) != null) {
throw new IllegalArgumentException(
"repeated interface: " + interfaceClass.getName());
}
}
//生成的代理類的包名
String proxyPkg = null; // package to define proxy class in
//代理類訪問控制符: public ,final
int accessFlags = Modifier.PUBLIC | Modifier.FINAL;
/*
* Record the package of a non-public proxy interface so that the
* proxy class will be defined in the same package. Verify that
* all non-public proxy interfaces are in the same package.
*/
//驗證全部非公共的接口在同一個包內；公共的就無需處理
//生成包名和類名的邏輯，包名默認是com.sun.proxy，類名默認是$Proxy 加上一個自增的整數值
//若是被代理類是 non-public proxy interface ，則用和被代理類接口同樣的包名
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.
*/
long num = nextUniqueNumber.getAndIncrement();
//代理類的徹底限定名，如com.sun.proxy.$Proxy0.calss
String proxyName = proxyPkg + proxyClassNamePrefix + num;
/*
* Generate the specified proxy class.
*/
//核心部分，生成代理類的字節碼
byte[] proxyClassFile = ProxyGenerator.generateProxyClass(
proxyName, interfaces, accessFlags);
try {
//把代理類加載到JVM中，至此動態代理過程基本結束了
return defineClass0(loader, proxyName,
proxyClassFile, 0, proxyClassFile.length);
} catch (ClassFormatError e) {
/*
* A ClassFormatError here means that (barring bugs in the
* proxy class generation code) there was some other
* invalid aspect of the arguments supplied to the proxy
* class creation (such as virtual machine limitations
* exceeded).
*/
throw new IllegalArgumentException(e.toString());
}
}
}
到這裏其實已經分析完了，可是本着深究的態度，決定看看JDK生成的動態代理字節碼是什麼，因而咱們將字節碼保存到磁盤上的class文件中。代碼以下：架構
public static void main(String[] args) {
IUserService target = new UserServiceImpl();
MyInvocationHandler handler = new MyInvocationHandler(target);
//第一個參數是指定代理類的類加載器（咱們傳入當前測試類的類加載器）
//第二個參數是代理類須要實現的接口（咱們傳入被代理類實現的接口，這樣生成的代理類和被代理類就實現了相同的接口）
//第三個參數是invocation handler，用來處理方法的調用。這裏傳入咱們本身實現的handler
IUserService proxyObject = (IUserService) Proxy.newProxyInstance(DynamicProxyTest.class.getClassLoader(),
target.getClass().getInterfaces(), handler);
proxyObject.add("張玉龍");
String path = "D:/$Proxy0.class";
byte[] classFile = ProxyGenerator.generateProxyClass("$Proxy0", HelloworldImpl.class.getInterfaces());
FileOutputStream out = null;
try {
out = new FileOutputStream(path);
out.write(classFile);
out.flush();
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
out.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
運行這段代碼，會在D盤生成一個名爲$Proxy0.class的文件。經過反編譯工具,獲得JDK爲咱們生成的代理類是這樣的：mvc
// Decompiled by Jad v1.5.8e2. Copyright 2001 Pavel Kouznetsov.
// Jad home page: http://kpdus.tripod.com/jad.html
// Decompiler options: packimports(3) fieldsfirst ansi space
import com.zhb.jdk.proxy.IUserService;
import java.lang.reflect.*;
public final class $Proxy0 extends Proxy
implements IUserService
{
private static Method m1;
private static Method m2;
private static Method m3;
private static Method m0;
//代理類的構造函數，其參數正是是InvocationHandler實例，
//Proxy.newInstance方法就是經過經過這個構造函數來建立代理實例的
public $Proxy0(InvocationHandler invocationhandler)
{
super(invocationhandler);
}
// Object類中的三個方法，equals，toString， hashCode
public final boolean equals(Object obj)
{
try
{
return ((Boolean)super.h.invoke(this, m1, new Object[] {
obj
})).booleanValue();
}
catch (Error ) { }
catch (Throwable throwable)
{
throw new UndeclaredThrowableException(throwable);
}
}
public final String toString()
{
try
{
return (String)super.h.invoke(this, m2, null);
}
catch (Error ) { }
catch (Throwable throwable)
{
throw new UndeclaredThrowableException(throwable);
}
}
//接口代理方法
public final void add(String s)
{
try
{
// invocation handler的 invoke方法在這裏被調用
super.h.invoke(this, m3, new Object[] {
s
});
return;
}
catch (Error ) { }
catch (Throwable throwable)
{
throw new UndeclaredThrowableException(throwable);
}
}
public final int hashCode()
{
try
{
// 在這裏調用了invoke方法。
return ((Integer)super.h.invoke(this, m0, null)).intValue();
}
catch (Error ) { }
catch (Throwable throwable)
{
throw new UndeclaredThrowableException(throwable);
}
}
// 靜態代碼塊對變量進行一些初始化工做
static
{
try
{
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("com.zhb.jdk.proxy.IUserService").getMethod("add", new Class[] {
Class.forName("java.lang.String")
});
m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);
}
catch (NoSuchMethodException nosuchmethodexception)
{
throw new NoSuchMethodError(nosuchmethodexception.getMessage());
}
catch (ClassNotFoundException classnotfoundexception)
{
throw new NoClassDefFoundError(classnotfoundexception.getMessage());
}
}
}
生成了Object類的三個方法：toString，hashCode，equals。還有咱們須要被代理的方法。
JDK代理類的cache clear機制
你們都知道、在項目中被代理的class愈來愈多，因此jdk會搞一個cache的方式來防止相同的代理接口重複生成class，影響性能不說，實現也不是很優雅，那麼如今就會有一個問題了，當classloader已經在內存中沒有依賴的時候，被代理的proxy class其實也沒有什麼意義了，這樣就須要清空無用的cache，java Proxy採用了很是巧妙的「弱引用機制」，咱們來看下面的代碼
咱們仍是繼續看get方法的源碼
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;
}
}
.......
}
其中源碼中有一個方法expungeStaleEntries、咱們進去這個方法一窺究竟
private void expungeStaleEntries() {
CacheKey<K> cacheKey;
while ((cacheKey = (CacheKey<K>)refQueue.poll()) != null) {
cacheKey.expungeFrom(map, reverseMap);
}
}
在看看expungeFrom方法源碼幹了些什麼
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);
}
}
}
代碼很清晰了，清空被代理的對象。如今的關鍵就是refQueue對象是怎麼來的。咱們繼續找一下跟refQueue相關的源碼、在get中還有一段代碼是這樣的
Object cacheKey = CacheKey.valueOf(key, refQueue);
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
}
.....
}
這樣看就很是清晰了、原來是CacheKey繼承了WeakReference弱引用機制，當弱引用依賴的key沒有引用的時候，當前失效的對象就會進入ReferenceQueue中來實現清空cache的功能、這種實現思路和ThreadLocal的實現原理是同樣的、你們有興趣能夠去閱讀如下相關源碼。
三:手把手寫基於接口的java代理
上面咱們分析了jdk動態代理源碼、那咱們是否是能夠本身用本身的方式去寫一個屬於本身的jdk代理呢，答案是能夠的
首先咱們寫一個基類，固然我並無在基類裏面寫什麼東西，只是模擬java中的proxy類而已，固然咱們也能夠豐富的去拓展一下這個類的方法，來實現更多的功能，讀者能夠經過讀完這篇文章以後本身去考慮一下如何來拓展。
1 package meituan.zylproxy.handlder; 2 public class ZylProxy { 3 public ZylProxy(){ 4 } 5 }
代理的核心接口，咱們去作代理的時候必定是經過反射去調用的，無論jdk也好仍是cglib也好，永遠也沒法脫離反射，咱們照貓畫虎，本身寫一個代理接口核心類，這並非什麼難題，看起來和jdk的核心類接口也沒有什麼區別。
1 package meituan.zylproxy.handlder; 2 3 import java.lang.reflect.Method; 4 5 public interface ZYLInvocationHandler { 6 7 public Object invoke(Object proxy, Method method, Object[] args) 8 throws Exception; 9 }
說明一下 第一個參數proxy是表明代理類，而不是用戶本身寫的原生類實現。參數Method是接口的方法,args是運行時參數列表，在運行時傳遞過來的實際上就是實現類的參數，好了，下面讓咱們去深刻核心。
咱們自定義兩個接口和接口的實現Idto，Idto2，和Dtoimpl以下：
1 package meituan.zylproxy.test.i; 2 3 public interface Idto { 4 5 public void add(); 6 7 public String get(); 8 9 }
package meituan.zylproxy.test.i; public interface Idto2 { public void adda(); public String geta(); }
package meituan.zylproxy.test.i.impl; import meituan.zylproxy.test.i.Idto; import meituan.zylproxy.test.i.Idto2; public class DtoImpl implements Idto,Idto2{ @Override public void add() { System.out.println("add"); } @Override public String get() { System.out.println("get"); return "return get"; } @Override public void adda() { System.out.println("adda"); } @Override public String geta() { System.out.println("geta"); return "return geta"; } }
這是幾個再簡單不過的接口和實現類了，也沒有什麼可說的。接下來咱們想對接口進行代理，無非是咱們動態將接口進行實現，從而達到對使用者進行自定義handle接口暴露而已，下面看一下咱們須要生成一個什麼樣的代理類。
import java.lang.reflect.Method; import meituan.zylproxy.handlder.ZylProxy; import meituan.zylproxy.handlder.ZYLInvocationHandler; import meituan.zylproxy.test.i.Idto; import meituan.zylproxy.test.i.Idto2; public class IdtoPorxy extends ZylProxy implements Idto, Idto2 { public ZYLInvocationHandler zYLInvocationHandler; public static Method add1; public static Method get2; public static Method adda3; public static Method geta4; static { try { add1 = Class.forName ( "meituan.zylproxy.test.i.Idto" ).getMethod ( "add", new Class[0] ); get2 = Class.forName ( "meituan.zylproxy.test.i.Idto" ).getMethod ( "get", new Class[0] ); adda3 = Class.forName ( "meituan.zylproxy.test.i.Idto2" ).getMethod ( "adda", new Class[0] ); geta4 = Class.forName ( "meituan.zylproxy.test.i.Idto2" ).getMethod ( "geta", new Class[0] ); } catch (Exception e) { } } public IdtoPorxy(ZYLInvocationHandler zYLInvocationHandler) { this.zYLInvocationHandler = zYLInvocationHandler; } public void add() { Object[] o = {}; try { this.zYLInvocationHandler.invoke ( this, add1, o ); return; } catch (Throwable e) { e.printStackTrace (); } } public java.lang.String get() { Object[] o = {}; try { return (java.lang.String) this.zYLInvocationHandler.invoke ( this, get2, o ); } catch (Exception e) { e.printStackTrace (); } return null; } public void adda() { Object[] o = {}; try { this.zYLInvocationHandler.invoke ( this, adda3, o ); return; } catch (Throwable e) { e.printStackTrace (); } } public java.lang.String geta() { Object[] o = {}; try { return (java.lang.String) this.zYLInvocationHandler.invoke ( this, geta4, o ); } catch (Exception e) { e.printStackTrace (); } return null; } }
這個類不是由用戶寫的，而是咱們動態生成的，對於jdk來講是生成了字節碼，對cglib來講是經過字節碼加強，其實實現的方式有多種，後面爲了更方便你們理解我用字符串的形式來動態生成這麼一個"傢伙"，先看看這個類幹了些什麼吧，也很簡單。
public class IdtoPorxy extends ZylProxy implements Idto, Idto2
首先是繼承了剛纔咱們所說的ZylProxy，留着從此拓展，能夠參照java的Proxy，而後而且動態的實現了這兩個接口。很簡單
public ZYLInvocationHandler zYLInvocationHandler;
public IdtoPorxy(ZYLInvocationHandler zYLInvocationHandler) {
this.zYLInvocationHandler = zYLInvocationHandler;
}
這個是經過構造函數傳進來一個handler對象，對實現類的操做都靠它了。
public static Method add1; public static Method get2; public static Method adda3; public static Method geta4; static { try { add1 = Class.forName ( "meituan.zylproxy.test.i.Idto" ).getMethod ( "add", new Class[0] ); get2 = Class.forName ( "meituan.zylproxy.test.i.Idto" ).getMethod ( "get", new Class[0] ); adda3 = Class.forName ( "meituan.zylproxy.test.i.Idto2" ).getMethod ( "adda", new Class[0] ); geta4 = Class.forName ( "meituan.zylproxy.test.i.Idto2" ).getMethod ( "geta", new Class[0] ); } catch (Exception e) { } }
枚舉出來全部的接口的方法，經過class.forname來獲取到Method元數據。備用
public void add() { Object[] o = {}; try { this.zYLInvocationHandler.invoke ( this, add1, o ); return; } catch (Throwable e) { e.printStackTrace (); } } public java.lang.String get() { Object[] o = {}; try { return (java.lang.String) this.zYLInvocationHandler.invoke ( this, get2, o ); } catch (Exception e) { e.printStackTrace (); } return null; } public void adda() { Object[] o = {}; try { this.zYLInvocationHandler.invoke ( this, adda3, o ); return; } catch (Throwable e) { e.printStackTrace (); } } public java.lang.String geta() { Object[] o = {}; try { return (java.lang.String) this.zYLInvocationHandler.invoke ( this, geta4, o ); } catch (Exception e) { e.printStackTrace (); } return null; }
上面是要枚舉出來全部的方法的實現，很簡單都一個模樣，把實現交給handler去作就能夠了。至於怎麼實現靠handler，咱們動態生成的這個類只負責委託，不作任何事情。看到這裏你們必定急不可待的想知道這個類怎麼生成的了，我把我寫的源碼給你們貼出來看一下。
package meituan.zylproxy.util; import java.lang.reflect.Method; import java.lang.reflect.Modifier; import meituan.zylproxy.test.i.Idto; import meituan.zylproxy.test.i.Idto2; public class ClassUtil { public static String mackProxyClass(Class<?> c) throws Exception{ if(!c.isInterface()){ throw new Exception("代理的類必須是接口"); } StringBuffer importsp = new StringBuffer(); importsp.append("import java.lang.reflect.Method;\n"); importsp.append("import meituan.zylproxy.handlder.ZylProxy;\n"); importsp.append("import meituan.zylproxy.handlder.ZYLInvocationHandler;\n"); importsp.append("import " +c.getName() + ";\n"); StringBuilder publicStaticMethods = new StringBuilder(); //public static Method add; StringBuilder publicMethods = new StringBuilder(); publicMethods.append("public ZYLInvocationHandler zYLInvocationHandler;\n"); StringBuilder constructorsp = new StringBuilder(); String interFaceName = c.getName().substring(c.getName().lastIndexOf(".")+1); constructorsp.append("public ").append("" + interFaceName + "Porxy"). append("(ZYLInvocationHandler zYLInvocationHandler) { " + "this.zYLInvocationHandler = zYLInvocationHandler;" + "}"); publicStaticMethods.append(" static { try { "); StringBuilder classsp = new StringBuilder(); classsp.append("public class").append(" " + interFaceName + "Porxy").append(" extends ZylProxy implements ").append(interFaceName).append("{"); StringBuilder allMethods = new StringBuilder(); Method[] Methods = c.getMethods(); int curr=0; for (Method m_:Methods) { curr++; publicMethods.append("public static Method ").append(m_.getName() + String.valueOf(curr)).append(";\n"); publicStaticMethods.append("").append(m_.getName() + String.valueOf(curr)).append("="); publicStaticMethods.append("Class.forName(\"" + c.getName() + "\")" + ".getMethod(\""+ m_.getName() +"\", "); StringBuilder sp =new StringBuilder(); StringBuilder spArgs = new StringBuilder(); spArgs.append("Object[] o ={"); //public sp.append(Modifier.toString(m_.getModifiers()).replace("abstract", "")).append(" "); //void | java.lang.String sp.append(m_.getReturnType().getName()).append(" "); //add()|get() sp.append(m_.getName().concat("(")); StringBuilder methodCLass = new StringBuilder(); if(m_.getParameterTypes().length>0){ Class<?>[] claszz = m_.getParameterTypes(); int methodOffset = 0; methodCLass.append("new Class[] { "); for (Class<?> c_ : claszz) { String paramStr = "obj" + String.valueOf(++methodOffset); spArgs.append(paramStr.concat(",")); sp.append(c_.getName().toString().concat(" ").concat(paramStr)).append(","); methodCLass.append("Class.forName(\"" + c_.getName()).append("\"),"); } sp = new StringBuilder(sp.substring(0, sp.length()-1)); spArgs = new StringBuilder(spArgs.substring(0, spArgs.length()-1)); methodCLass = new StringBuilder(methodCLass.substring(0, methodCLass.length()-1)); } if(methodCLass.length()>0){ methodCLass.append("}"); } else{ methodCLass.append("new Class[0]"); } sp.append("){\n"); spArgs.append("}"); sp.append(spArgs+";\n"); if(sp.toString().contains("void")){ sp.append("try {\n this.zYLInvocationHandler.invoke(this,").append(m_.getName() + String.valueOf(curr)).append(",").append("o);\n return;\n"); sp.append("} catch (Throwable e) {e.printStackTrace();}}"); } else{ sp.append("try {return " + "(" + m_.getReturnType().getName() + ")" + "this.zYLInvocationHandler.invoke(this,").append(m_.getName() + String.valueOf(curr)).append(",").append("o);\n"); sp.append("} catch (Exception e) {e.printStackTrace();} return null;"); } publicStaticMethods.append(methodCLass).append(");\n"); allMethods.append(sp); } publicStaticMethods.append("} catch(Exception e){}}"); classsp.append(publicMethods) .append(publicStaticMethods) .append(constructorsp).append(allMethods).append("}"); classsp.append("}"); importsp.append(classsp); return importsp.toString(); } public static String mackMultiProxyClass(Class<?>[] cs) throws Exception{ StringBuffer importsp = new StringBuffer(); importsp.append("import java.lang.reflect.Method;\n"); importsp.append("import meituan.zylproxy.handlder.ZylProxy;\n"); importsp.append("import meituan.zylproxy.handlder.ZYLInvocationHandler;\n"); StringBuilder publicStaticMethods = new StringBuilder(); publicStaticMethods.append(" static { try { "); //public static Method add; StringBuilder publicMethods = new StringBuilder(); publicMethods.append("public ZYLInvocationHandler zYLInvocationHandler;\n"); int curr=0; StringBuilder constructorsp = new StringBuilder(); String interFaceName = cs[0].getName().substring(cs[0].getName().lastIndexOf(".")+1); constructorsp.append("public ").append("" + interFaceName + "Porxy"). append("(ZYLInvocationHandler zYLInvocationHandler) { " + "this.zYLInvocationHandler = zYLInvocationHandler;" + "}"); StringBuilder allMethods = new StringBuilder(); StringBuilder classsp = new StringBuilder(); classsp.append("public class").append(" " + interFaceName + "Porxy").append(" extends ZylProxy implements "); for (Class<?> c:cs) { if(!c.isInterface()){ throw new Exception("代理的類必須是接口"); } classsp.append(c.getName().substring(c.getName().lastIndexOf(".")+1)).append(","); importsp.append("import " +c.getName() + ";\n"); Method[] Methods = c.getMethods(); for (Method m_:Methods) { curr++; publicMethods.append("public static Method ").append(m_.getName() + String.valueOf(curr)).append(";\n"); publicStaticMethods.append("").append(m_.getName() + String.valueOf(curr)).append("="); publicStaticMethods.append("Class.forName(\"" + c.getName() + "\")" + ".getMethod(\""+ m_.getName() +"\", "); StringBuilder sp =new StringBuilder(); StringBuilder spArgs = new StringBuilder(); spArgs.append("Object[] o ={"); //public sp.append(Modifier.toString(m_.getModifiers()).replace("abstract", "")).append(" "); //void | java.lang.String sp.append(m_.getReturnType().getName()).append(" "); //add()|get() sp.append(m_.getName().concat("(")); StringBuilder methodCLass = new StringBuilder(); if(m_.getParameterTypes().length>0){ Class<?>[] claszz = m_.getParameterTypes(); int methodOffset = 0; methodCLass.append("new Class[] { "); for (Class<?> c_ : claszz) { String paramStr = "obj" + String.valueOf(++methodOffset); spArgs.append(paramStr.concat(",")); sp.append(c_.getName().toString().concat(" ").concat(paramStr)).append(","); methodCLass.append("Class.forName(\"" + c_.getName()).append("\"),"); } sp = new StringBuilder(sp.substring(0, sp.length()-1)); spArgs = new StringBuilder(spArgs.substring(0, spArgs.length()-1)); methodCLass = new StringBuilder(methodCLass.substring(0, methodCLass.length()-1)); } if(methodCLass.length()>0){ methodCLass.append("}"); } else{ methodCLass.append("new Class[0]"); } sp.append("){\n"); spArgs.append("}"); sp.append(spArgs+";\n"); if(sp.toString().contains("void")){ sp.append("try {\n this.zYLInvocationHandler.invoke(this,").append(m_.getName() + String.valueOf(curr)).append(",").append("o);\n return;\n"); sp.append("} catch (Throwable e) {e.printStackTrace();}}"); } else{ sp.append("try {return " + "(" + m_.getReturnType().getName() + ")" + "this.zYLInvocationHandler.invoke(this,").append(m_.getName() + String.valueOf(curr)).append(",").append("o);\n"); sp.append("} catch (Exception e) {e.printStackTrace();} return null;}"); } publicStaticMethods.append(methodCLass).append(");\n"); allMethods.append(sp); } } classsp = new StringBuilder(classsp.substring(0, classsp.length()-1)).append("{"); publicStaticMethods.append("} catch(Exception e){}}"); classsp.append(publicMethods) .append(publicStaticMethods) .append(constructorsp).append(allMethods).append(""); classsp.append("}"); importsp.append(classsp); return importsp.toString(); } public static void main(String[] args) throws Exception { System.out.println(mackMultiProxyClass(new Class<?>[]{Idto.class})); } }
看起來很複雜，仔細看一下就看了那麼幾個事情，把一個接口class或者多個接口class變成純字符串的過程，一共兩個方法，一個是單接口的實現，很早以前寫的，第二個方法是多接口的實現支持多接口，只須要傳一個class對象就會生成代理類的字符串，這裏僅僅是字符串，須要編譯成class使用。那麼如何編譯成class呢。經過java中的工具類 JavaCompiler很簡單的就能夠生成了。咱們來看兩個工具類實現
package meituan.zylproxy; import java.io.ByteArrayOutputStream; import java.io.File; import java.io.FilterOutputStream; import java.io.IOException; import java.io.OutputStream; import java.io.Reader; import java.io.StringReader; import java.net.URI; import java.nio.CharBuffer; import java.nio.file.WatchEvent.Kind; import java.util.HashMap; import java.util.Map; import javax.tools.FileObject; import javax.tools.ForwardingJavaFileManager; import javax.tools.JavaFileManager; import javax.tools.JavaFileObject; import javax.tools.SimpleJavaFileObject; @SuppressWarnings("unchecked") final class MemoryJavaFileManager extends ForwardingJavaFileManager { private final static String EXT = ".java"; private Map<String, byte[]> classBytes; public MemoryJavaFileManager(JavaFileManager fileManager) { super(fileManager); classBytes = new HashMap<String, byte[]>(); } public Map<String, byte[]> getClassBytes() { return classBytes; } public void close() throws IOException { classBytes = new HashMap<String, byte[]>(); } public void flush() throws IOException { } private static class StringInputBuffer extends SimpleJavaFileObject { final String code; StringInputBuffer(String name, String code) { super(toURI(name), Kind.SOURCE); this.code = code; } public CharBuffer getCharContent(boolean ignoreEncodingErrors) { return CharBuffer.wrap(code); } public Reader openReader() { return new StringReader(code); } } private class ClassOutputBuffer extends SimpleJavaFileObject { private String name; ClassOutputBuffer(String name) { super(toURI(name), Kind.CLASS); this.name = name; } public OutputStream openOutputStream() { return new FilterOutputStream(new ByteArrayOutputStream()) { public void close() throws IOException { out.close(); ByteArrayOutputStream bos = (ByteArrayOutputStream) out; classBytes.put(name, bos.toByteArray()); } }; } } public JavaFileObject getJavaFileForOutput(JavaFileManager.Location location, String className, JavaFileObject.Kind kind, FileObject sibling) throws IOException { if (kind == JavaFileObject.Kind.CLASS) { return new ClassOutputBuffer(className); } else { return super.getJavaFileForOutput(location, className, kind, sibling); } } static JavaFileObject makeStringSource(String name, String code) { return new StringInputBuffer(name, code); } static URI toURI(String name) { File file = new File(name); if (file.exists()) { return file.toURI(); } else { try { final StringBuilder newUri = new StringBuilder(); newUri.append("mfm:///"); newUri.append(name.replace('.', '/')); if (name.endsWith(EXT)) newUri.replace(newUri.length() - EXT.length(), newUri.length(), EXT); return URI.create(newUri.toString()); } catch (Exception exp) { return URI.create("mfm:///com/sun/script/java/java_source"); } } } }
package meituan.zylproxy; import java.io.IOException; import java.net.URL; import java.net.URLClassLoader; import java.util.Arrays; import java.util.HashMap; import java.util.Map; import java.util.regex.Matcher; import java.util.regex.Pattern; import javax.tools.JavaCompiler; import javax.tools.JavaFileObject; import javax.tools.StandardJavaFileManager; import javax.tools.ToolProvider; public class DynamicLoader { public static Map<String, byte[]> compile(String javaSrc) { Pattern pattern = Pattern.compile("public\\s+class\\s+(\\w+)"); Matcher matcher = pattern.matcher(javaSrc); if (matcher.find()) return compile(matcher.group(1) + ".java", javaSrc); return null; } public static Map<String, byte[]> compile(String javaName, String javaSrc) { JavaCompiler compiler = ToolProvider.getSystemJavaCompiler(); StandardJavaFileManager stdManager = compiler.getStandardFileManager(null, null, null); try (MemoryJavaFileManager manager = new MemoryJavaFileManager(stdManager)) { JavaFileObject javaFileObject = manager.makeStringSource(javaName, javaSrc); JavaCompiler.CompilationTask task = compiler.getTask(null, manager, null, null, null, Arrays.asList(javaFileObject)); if (task.call()) return manager.getClassBytes(); } catch (IOException e) { e.printStackTrace(); } return null; } public static class MemoryClassLoader extends URLClassLoader { Map<String, byte[]> classBytes = new HashMap<String, byte[]>(); public MemoryClassLoader(Map<String, byte[]> classBytes) { super(new URL[0], MemoryClassLoader.class.getClassLoader()); this.classBytes.putAll(classBytes); } @Override protected Class<?> findClass(String name) throws ClassNotFoundException { byte[] buf = classBytes.get(name); if (buf == null) { return super.findClass(name); } classBytes.remove(name); return defineClass(name, buf, 0, buf.length); } } }
經過DynamicLoader的compile方法能夠把純字符串的str轉成byte[]數組，有了byte[]數組就能夠很方便的獲取到class對象了，自定義一個MemoryClassLoader經過defineClass方法來獲取到class對象。這樣基本全部的事情都作完了。下面咱們寫一個工廠類來獲取代理類。
package meituan.zylproxy.util; import java.util.Map; import meituan.zylproxy.DynamicLoader; import meituan.zylproxy.handlder.ZYLInvocationHandler; public class PorxyFactory { //單interface的時候用 public static Object newProxyInstance(Class<?> c,ZYLInvocationHandler h) throws Exception{ String classStr = ClassUtil.mackProxyClass(c); Map<String, byte[]> m = DynamicLoader.compile(classStr); DynamicLoader.MemoryClassLoader classLoader = new DynamicLoader.MemoryClassLoader(m); Class<?> proxy =classLoader.loadClass(m.keySet().toArray(new String[0])[0]); return proxy.getConstructor(ZYLInvocationHandler.class).newInstance(h); } //多interface的時候用 public static Object newProxyInstancewWithMultiClass(Class<?>[] c,ZYLInvocationHandler h) throws Exception{ String classStr = ClassUtil.mackMultiProxyClass(c); System.out.println (classStr); Map<String, byte[]> m = DynamicLoader.compile(classStr); DynamicLoader.MemoryClassLoader classLoader = new DynamicLoader.MemoryClassLoader(m); Class<?> proxy =classLoader.loadClass(m.keySet().toArray(new String[0])[0]); return proxy.getConstructor(ZYLInvocationHandler.class).newInstance(h); } }
最後一步咱們測試一下結果吧，寫一個測試類
package meituan.zylproxy.test; import meituan.zylproxy.handlder.Hander; import meituan.zylproxy.test.i.Idto; import meituan.zylproxy.test.i.impl.DtoImpl; import meituan.zylproxy.util.PorxyFactory; public class ZylPorxyTest { public static void main(String[] args) throws Exception { Idto d = (Idto) PorxyFactory.newProxyInstancewWithMultiClass(DtoImpl.class.getInterfaces(), new Hander(new DtoImpl())); d.add(); } }
很簡單，第一個參數是全部的接口，第二個是handler實現。最後咱們看看結果。
大功告成。
做者簡介：就任美團外賣業務架構組，有更多的更多的源碼交流，請加羣825199617交流，spring源碼，spring mvc源碼，手寫企業級高可用rpc框架，java企業級熱部署解決方案等等更多精彩源碼，等你來。