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這篇文章將為大家詳細(xì)講解有關(guān)Springboot中TargetSource的作用是什么,文章內(nèi)容質(zhì)量較高,因此小編分享給大家做個參考,希望大家閱讀完這篇文章后對相關(guān)知識有一定的了解。
其實proxy
代理的不是target
,而是TargetSource
,這點非常重要,一定要分清楚!??!
通常情況下,一個代理對象只能代理一個target,每次方法調(diào)用的目標(biāo)也是唯一固定的target。但是,如果讓proxy代理TargetSource,可以使得每次方法調(diào)用的target實例都不同(當(dāng)然也可以相同,這取決于TargetSource實現(xiàn))。這種機(jī)制使得方法調(diào)用變得靈活,可以擴(kuò)展出很多高級功能,如:單利,原型,本地線程,目標(biāo)對象池、運行時目標(biāo)對象熱替換目標(biāo)源等等。
public class SingletonTargetSource implements TargetSource, Serializable { /** Target cached and invoked using reflection. */ private final Object target; //省略無關(guān)代碼...... @Override public Object getTarget() { return this.target; } //省略無關(guān)代碼...... }
從這個目標(biāo)源取得的目標(biāo)對象是單例的,成員變量target緩存了目標(biāo)對象,每次getTarget()
都是返回這個對象。
public class PrototypeTargetSource extends AbstractPrototypeBasedTargetSource { /** * Obtain a new prototype instance for every call. * @see #newPrototypeInstance() */ @Override public Object getTarget() throws BeansException { return newPrototypeInstance(); } /** * Destroy the given independent instance. * @see #destroyPrototypeInstance */ @Override public void releaseTarget(Object target) { destroyPrototypeInstance(target); } //省略無關(guān)代碼...... }
每次getTarget()
將生成prototype
類型的bean,即其生成的bean并不是單例的,因而使用這個類型的TargetSource
時需要注意,封裝的目標(biāo)bean必須是prototype類型的。PrototypeTargetSource
繼承了AbstractBeanFactoryBasedTargetSource
擁有了創(chuàng)建bean的能力。
public abstract class AbstractPrototypeBasedTargetSource extends AbstractBeanFactoryBasedTargetSource { //省略無關(guān)代碼...... /** * Subclasses should call this method to create a new prototype instance. * @throws BeansException if bean creation failed */ protected Object newPrototypeInstance() throws BeansException { if (logger.isDebugEnabled()) { logger.debug("Creating new instance of bean '" + getTargetBeanName() + "'"); } return getBeanFactory().getBean(getTargetBeanName()); } /** * Subclasses should call this method to destroy an obsolete prototype instance. * @param target the bean instance to destroy */ protected void destroyPrototypeInstance(Object target) { if (logger.isDebugEnabled()) { logger.debug("Destroying instance of bean '" + getTargetBeanName() + "'"); } if (getBeanFactory() instanceof ConfigurableBeanFactory) { ((ConfigurableBeanFactory) getBeanFactory()).destroyBean(getTargetBeanName(), target); } else if (target instanceof DisposableBean) { try { ((DisposableBean) target).destroy(); } catch (Throwable ex) { logger.warn("Destroy method on bean with name '" + getTargetBeanName() + "' threw an exception", ex); } } } //省略無關(guān)代碼...... }
可以看到,PrototypeTargetSource
的生成prototype類型bean的方式主要是委托給BeanFactory
進(jìn)行的,因為BeanFactory自有一套生成prototype類型的bean的邏輯,因而PrototypeTargetSource
也就具有生成prototype類型bean的能力,這也就是我們要生成的目標(biāo)bean必須聲明為prototype類型的原因。
public class ThreadLocalTargetSource extends AbstractPrototypeBasedTargetSource implements ThreadLocalTargetSourceStats, DisposableBean { /** * ThreadLocal holding the target associated with the current * thread. Unlike most ThreadLocals, which are static, this variable * is meant to be per thread per instance of the ThreadLocalTargetSource class. */ private final ThreadLocal<Object> targetInThread = new NamedThreadLocal<>("Thread-local instance of bean '" + getTargetBeanName() + "'"); /** * Set of managed targets, enabling us to keep track of the targets we've created. */ private final Set<Object> targetSet = new HashSet<>(); //省略無關(guān)代碼...... /** * Implementation of abstract getTarget() method. * We look for a target held in a ThreadLocal. If we don't find one, * we create one and bind it to the thread. No synchronization is required. */ @Override public Object getTarget() throws BeansException { ++this.invocationCount; Object target = this.targetInThread.get(); if (target == null) { if (logger.isDebugEnabled()) { logger.debug("No target for prototype '" + getTargetBeanName() + "' bound to thread: " + "creating one and binding it to thread '" + Thread.currentThread().getName() + "'"); } // Associate target with ThreadLocal. target = newPrototypeInstance(); this.targetInThread.set(target); synchronized (this.targetSet) { this.targetSet.add(target); } } else { ++this.hitCount; } return target; } /** * Dispose of targets if necessary; clear ThreadLocal. * @see #destroyPrototypeInstance */ @Override public void destroy() { logger.debug("Destroying ThreadLocalTargetSource bindings"); synchronized (this.targetSet) { for (Object target : this.targetSet) { destroyPrototypeInstance(target); } this.targetSet.clear(); } // Clear ThreadLocal, just in case. this.targetInThread.remove(); } //省略無關(guān)代碼...... }
ThreadLocalTargetSource
也就是和線程綁定的TargetSource
,可以理解,其底層實現(xiàn)必然使用的是ThreadLocal。既然使用了ThreadLocal
,也就是說我們需要注意兩個問題:
目標(biāo)對象必須聲明為prototype類型,因為每個線程都會持有一個不一樣的對象;
目標(biāo)對象必須是無狀態(tài)的,因為目標(biāo)對象是和當(dāng)前線程綁定的,而Spring是使用的線程池處理的請求,因而每個線程可能處理不同的請求,因而為了避免造成問題,目標(biāo)對象必須是無狀態(tài)的。
package com.github.dqqzj.springboot.target; import org.springframework.aop.TargetSource; import org.springframework.util.Assert; import java.lang.reflect.Array; import java.util.concurrent.ThreadLocalRandom; import java.util.concurrent.atomic.AtomicInteger; /** * @author qinzhongjian * @date created in 2019-08-25 12:43 * @description: TODO * @since JDK 1.8.0_212-b10z */ public class DqqzjTargetSource implements TargetSource { private final AtomicInteger idx = new AtomicInteger(); private final Object[] target;; public DqqzjTargetSource(Object[] target) { Assert.notNull(target, "Target object must not be null"); this.target = target; } @Override public Class<?> getTargetClass() { return target.getClass(); } @Override public boolean isStatic() { return false; } @Override public Object getTarget() throws Exception { return this.target[this.idx.getAndIncrement() & this.target.length - 1]; } @Override public void releaseTarget(Object target) throws Exception { } }
實現(xiàn)自定義TargetSource主要有兩個點要注意,一個是getTarget()
方法,該方法中需要實現(xiàn)獲取目標(biāo)對象的邏輯,另一個是isStatic()
方法,這個方法告知Spring是否需要緩存目標(biāo)對象,在非單例的情況下一般是返回false
。
關(guān)于Springboot中TargetSource的作用是什么就分享到這里了,希望以上內(nèi)容可以對大家有一定的幫助,可以學(xué)到更多知識。如果覺得文章不錯,可以把它分享出去讓更多的人看到。
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