Spring AOP原理之動態(tài)代理
什么是代理?
指為一個目標(biāo)對象提供一個代理對象, 并由代理對象控制對目標(biāo)對象的引用. 使用代理對象, 是為了在不修改目標(biāo)對象的基礎(chǔ)上, 增強(qiáng)目標(biāo)對象的業(yè)務(wù)邏輯.
靜態(tài)代理
靜態(tài)代理的特點(diǎn)是, 為每一個業(yè)務(wù)增強(qiáng)都提供一個代理類, 由代理類來創(chuàng)建代理對象. 下面我們通過靜態(tài)代理來實(shí)現(xiàn)對轉(zhuǎn)賬業(yè)務(wù)進(jìn)行身份驗證.
(1) 轉(zhuǎn)賬業(yè)務(wù)
public?interface?IAccountService?{
????//主業(yè)務(wù)邏輯: 轉(zhuǎn)賬
????void?transfer();
}
public?class?AccountServiceImpl?implements?IAccountService?{
????@Override
????public?void?transfer()?{
????????System.out.println("調(diào)用dao層,完成轉(zhuǎn)賬主業(yè)務(wù).");
????}
}(2) 代理類
public?class?AccountProxy?implements?IAccountService?{
????//目標(biāo)對象
????private?IAccountService target;
????public?AccountProxy(IAccountService target) {
????????this.target = target;
????}
????/**
?????* 代理方法,實(shí)現(xiàn)對目標(biāo)方法的功能增強(qiáng)
?????*/
????@Override
????public?void?transfer() {
????????before();
????????target.transfer();
????}
????/**
?????* 前置增強(qiáng)
?????*/
????private?void?before() {
????????System.out.println("對轉(zhuǎn)賬人身份進(jìn)行驗證.");
????}
}(3) 測試
public?class?Client?{
????public?static?void?main(String[] args)?{
????????//創(chuàng)建目標(biāo)對象
????????IAccountService target = new?AccountServiceImpl();
????????//創(chuàng)建代理對象
????????AccountProxy proxy = new?AccountProxy(target);
????????proxy.transfer();
????}
}
結(jié)果:
對轉(zhuǎn)賬人身份進(jìn)行驗證.
調(diào)用dao層,完成轉(zhuǎn)賬主業(yè)務(wù).動態(tài)代理
靜態(tài)代理會為每一個業(yè)務(wù)增強(qiáng)都提供一個代理類, 由代理類來創(chuàng)建代理對象, 而動態(tài)代理并不存在代理類, 代理對象直接由代理生成工具動態(tài)生成.
JDK動態(tài)代理
JDK動態(tài)代理是使用 java.lang.reflect 包下的代理類來實(shí)現(xiàn). JDK動態(tài)代理動態(tài)代理必須要有接口.
(1) 轉(zhuǎn)賬業(yè)務(wù)
public?interface?IAccountService?{
????//主業(yè)務(wù)邏輯: 轉(zhuǎn)賬
????void?transfer();
}
public?class?AccountServiceImpl?implements?IAccountService?{
????@Override
????public?void?transfer()?{
????????System.out.println("調(diào)用dao層,完成轉(zhuǎn)賬主業(yè)務(wù).");
????}
}(2) 增強(qiáng)
因為這里沒有配置切入點(diǎn), 稱為切面會有點(diǎn)奇怪, 所以稱為增強(qiáng).
public?class?AccountAdvice?implements?InvocationHandler?{
????//目標(biāo)對象
????private?IAccountService target;
????public?AccountAdvice(IAccountService target)?{
????????this.target = target;
????}
????/**
?????* 代理方法, 每次調(diào)用目標(biāo)方法時都會進(jìn)到這里
?????*/
????@Override
????public?Object invoke(Object proxy, Method method, Object[] args)?throws?Throwable {
????????before();
????????return?method.invoke(target, args);
????}
????/**
?????* 前置增強(qiáng)
?????*/
????private?void?before()?{
????????System.out.println("對轉(zhuǎn)賬人身份進(jìn)行驗證.");
????}
}(3) 測試
public?class?Client?{
????public?static?void?main(String[] args)?{
????????//創(chuàng)建目標(biāo)對象
????????IAccountService target = new?AccountServiceImpl();
????????//創(chuàng)建代理對象
????????IAccountService proxy = (IAccountService) Proxy.newProxyInstance(target.getClass().getClassLoader(),
????????????????target.getClass().getInterfaces(),
????????????????new?AccountAdvice(target)
????????);
????????proxy.transfer();
????}
}
結(jié)果:
對轉(zhuǎn)賬人身份進(jìn)行驗證.
調(diào)用dao層,完成轉(zhuǎn)賬主業(yè)務(wù).CGLIB動態(tài)代理
JDK動態(tài)代理必須要有接口, 但如果要代理一個沒有接口的類該怎么辦呢? 這時我們可以使用CGLIB動態(tài)代理. CGLIB動態(tài)代理的原理是生成目標(biāo)類的子類, 這個子類對象就是代理對象, 代理對象是被增強(qiáng)過的.
注意: 不管有沒有接口都可以使用CGLIB動態(tài)代理, 而不是只有在無接口的情況下才能使用.
(1) 轉(zhuǎn)賬業(yè)務(wù)
public?class?AccountService?{
????public?void?transfer() {
????????System.out.println("調(diào)用dao層,完成轉(zhuǎn)賬主業(yè)務(wù).");
????}
}(2) 增強(qiáng)
因為這里沒有配置切入點(diǎn), 稱為切面會有點(diǎn)奇怪, 所以稱為增強(qiáng).
public?class?AccountAdvice implements?MethodInterceptor {
????/**
?????* 代理方法, 每次調(diào)用目標(biāo)方法時都會進(jìn)到這里
?????*/
????@Override
????public?Object?intercept(Object?obj, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
????????before();
????????return?methodProxy.invokeSuper(obj, args);
????????// return method.invoke(obj, args); 這種也行
????}
????/**
?????* 前置增強(qiáng)
?????*/
????private?void?before() {
????????System.out.println("對轉(zhuǎn)賬人身份進(jìn)行驗證.");
????}
}(3) 測試
public?class?Client?{
????public?static?void?main(String[] args)?{
????????//創(chuàng)建目標(biāo)對象
????????AccountService target = new?AccountService();
????????//
????????//創(chuàng)建代理對象
????????AccountService proxy = (AccountService) Enhancer.create(target.getClass(),
????????????????new?AccountAdvice());
????????proxy.transfer();
????}
}
結(jié)果:
對轉(zhuǎn)賬人身份進(jìn)行驗證.
調(diào)用dao層,完成轉(zhuǎn)賬主業(yè)務(wù).模擬Spring AOP場景
了解了動態(tài)代理后, 我們就可以自己來實(shí)現(xiàn)Spring AOP功能了, 所以下面我們來模擬下Spring AOP場景.
(1) 轉(zhuǎn)賬業(yè)務(wù)
public?class?Client?{
????public?static?void?main(String[] args)?{
????????//創(chuàng)建目標(biāo)對象
????????AccountService target = new?AccountService();
????????//
????????//創(chuàng)建代理對象
????????AccountService proxy = (AccountService) Enhancer.create(target.getClass(),
????????????????new?AccountAdvice());
????????proxy.transfer();
????}
}
結(jié)果:
對轉(zhuǎn)賬人身份進(jìn)行驗證.
調(diào)用dao層,完成轉(zhuǎn)賬主業(yè)務(wù).(2) 切面抽象類
定義一個切面抽象類, 該類使用了模板方法的設(shè)計模式, 為開始, 結(jié)束, 異常, 前置增強(qiáng), 后置增強(qiáng)提供了默認(rèn)實(shí)現(xiàn), 當(dāng)我們定義切面類時只需要按需重寫它們就行. isIntercept() 方法用來判斷切入點(diǎn)是否正確, 切面類需要重寫這個方法.
public?abstract?class?BaseAspect?implements?MethodInterceptor?{
????private?static?final?Logger logger = LoggerFactory.getLogger(BaseAspect.class);
????@Override
????public?Object intercept(Object obj, Method method, Object[] args, MethodProxy methodProxy)?throws?Throwable {
????????Object result = null;
????????begin();
????????try?{
????????????if?(isIntercept(method, args)) {
????????????????before();
????????????????result = methodProxy.invokeSuper(obj, args);
????????????????after();
????????????} else?{
????????????????result = methodProxy.invokeSuper(obj,args);
????????????}
????????} catch?(Exception e) {
????????????logger.error("proxy failure", e);
????????????error(e);
????????????throw?e;
????????} finally?{
????????????end();
????????}
????????return?result;
????}
????/**
?????* 開始增強(qiáng)
?????*/
????public?void?begin()?{
????}
????/**
?????* 切入點(diǎn)判斷
?????*/
????public?boolean?isIntercept(Method method, Object[] args)?throws?Throwable {
????????return?true;
????}
????/**
?????* 前置增強(qiáng)
?????*/
????public?void?before()?throws?Throwable {
????}
????/**
?????* 后置增強(qiáng)
?????*/
????public?void?after()?throws?Throwable {
????}
????/**
?????* 異常增強(qiáng)
?????*/
????public?void?error(Throwable e)?{
????}
????/**
?????* 最終增強(qiáng)
?????*/
????public?void?end()?{
????}
}(3) 切面類
創(chuàng)建一個切面類, 類中配置切入點(diǎn)和增強(qiáng).
public?class?AccountAspect?extends?BaseAspect?{
????/**
?????* 切入點(diǎn)
?????*/
????public?boolean?isIntercept(Method method, Object[] args)?throws?Throwable {
????????return?method.getName().equals("transfer");
????}
????/**
?????* 前置增強(qiáng)
?????*/
????public?void?before()?throws?Throwable {
????????System.out.println("對轉(zhuǎn)賬人身份進(jìn)行驗證.");
????}
}(4) 代理工廠類
定義一個工廠類來創(chuàng)建代理, 其實(shí)不創(chuàng)建這個類也行, 但為了模仿Spring還是創(chuàng)建了. @SuppressWarnings是為了抑制警告, 就是編譯器上面的黃線.
public?class?ProxyFactory?{
????@SuppressWarnings("unchecked")
????public?static? T createProxy(final?Class targetClass, final?MethodInterceptor methodInterceptor)?{
????????return?(T) Enhancer.create(targetClass,methodInterceptor);
????}
} (5) 測試
public?class?Client?{
????public?static?void?main(String[] args)?{
????????//創(chuàng)建目標(biāo)對象
????????IAccountService target = new?AccountServiceImpl();
????????//切面
????????BaseAspect accountAspect = new?AccountAspect();
????????//創(chuàng)建代理對象
????????IAccountService proxy = (IAccountService) ProxyFactory.createProxy(target.getClass(), accountAspect);
????????proxy.transfer();
????}
}
結(jié)果:
對轉(zhuǎn)賬人身份進(jìn)行驗證.
調(diào)用dao層,完成轉(zhuǎn)賬主業(yè)務(wù).原文鏈接：csdn.net/litianxiang_kaola/article/details/85335700
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