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‎Cache/Cache.iml‎

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<?xml version="1.0" encoding="UTF-8"?>
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<module type="JAVA_MODULE" version="4">
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<component name="NewModuleRootManager" inherit-compiler-output="true">
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<exclude-output />
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<content url="file://$MODULE_DIR$">
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<sourceFolder url="file://$MODULE_DIR$/src" isTestSource="false" />
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</content>
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<orderEntry type="inheritedJdk" />
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<orderEntry type="sourceFolder" forTests="false" />
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</component>
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</module>

‎Cache/src/CacheUsage1.java‎

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import java.util.HashMap;
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import java.util.concurrent.TimeUnit;
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/**
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* 最简单的缓存形式 -> HashMap
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* 性能差 + 代码复用性差（侵入性高） + 并发不安全
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*
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* @Author: zzStar
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* @Date: 10-13-2020 12:43
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*/
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public class CacheUsage1 {
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private final HashMap<String, Integer> cache = new HashMap<>();
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public synchronized Integer computer(String userId) throws InterruptedException {
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//先检查hashmap里面有没有保存过之前的计算结果
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Integer result = cache.get(userId);
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if (result == null) {
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//缓存中没有，则现在计算,计算后保存到cache里
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result = doCompute(userId);
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cache.put(userId, result);
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}
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return result;
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}
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//业务代码
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private Integer doCompute(String userId) throws InterruptedException {
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TimeUnit.SECONDS.sleep(1);
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return Integer.valueOf(userId);
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}
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public static void main(String[] args) throws InterruptedException {
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CacheUsage1 cacheUsage1 = new CacheUsage1();
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System.out.println("calculating");
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Integer result = cacheUsage1.computer("13");
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System.out.println("result = " + result);
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result = cacheUsage1.computer("13");
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System.out.println("result = " + result);
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}
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}

‎Cache/src/CacheUsage2.java‎

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import java.util.HashMap;
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/**
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* 装饰者模式解耦
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*
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* @Author: zzStar
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* @Date: 10-13-2020 13:03
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*/
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public class CacheUsage2<A, V> implements Computable<A, V> {
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private final HashMap<A, V> cache = new HashMap<>();
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private final Computable<A, V> computable;
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public CacheUsage2(Computable<A, V> computable) {
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this.computable = computable;
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}
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@Override
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public synchronized V compute(A arg) throws Exception {
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System.out.println("cache");
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V result = cache.get(arg);
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if (result == null) {
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result = computable.compute(arg);
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cache.put(arg, result);
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}
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return result;
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}
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public static void main(String[] args) throws Exception {
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CacheUsage2<String, Integer> usage2 = new CacheUsage2<>(new ExpensiveFunc());
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Integer result = usage2.compute("1333");
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System.out.println("result = " + result);
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result = usage2.compute("1333");
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System.out.println("result = " + result);
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}
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}

‎Cache/src/CacheUsage3.java‎

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import java.util.HashMap;
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/**
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* 多线程访问的性能问题:在多线程的情况下,只能一个线程进入cache 的计算方法
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*
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* @Author: zzStar
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* @Date: 10-13-2020 13:03
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*/
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public class CacheUsage3<A, V> implements Computable<A, V> {
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private final HashMap<A, V> cache = new HashMap<>();
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private final Computable<A, V> computable;
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public CacheUsage3(Computable<A, V> computable) {
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this.computable = computable;
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}
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/*
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@Override
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public synchronized V compute(A arg) throws Exception {
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System.out.println(Thread.currentThread().getName() + " 进入缓存机制");
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V result = cache.get(arg);
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if (result == null) {
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result = computable.compute(arg);
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cache.put(arg, result);
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}
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return result;
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}
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*/
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//缩小锁的粒度,仍不意味着线程安全，还需要考虑到同时读写等情况
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@Override
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public V compute(A arg) throws Exception {
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System.out.println(Thread.currentThread().getName() + " 进入缓存机制");
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V result = cache.get(arg);
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if (result == null) {
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result = computable.compute(arg);
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synchronized (this) {
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cache.put(arg, result);
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}
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}
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return result;
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}
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public static void main(String[] args) {
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CacheUsage3<String, Integer> usage3 = new CacheUsage3<>(new ExpensiveFunc());
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new Thread(() -> {
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try {
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Integer result = usage3.compute("7878");
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System.out.println(Thread.currentThread().getName() + " result=" + result);
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} catch (Exception e) {
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e.printStackTrace();
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}
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}).start();
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new Thread(() -> {
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try {
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Integer result = usage3.compute("7878");
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System.out.println(Thread.currentThread().getName() + " result=" + result);
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} catch (Exception e) {
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e.printStackTrace();
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}
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}).start();
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new Thread(() -> {
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try {
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Integer result = usage3.compute("8989");
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System.out.println(Thread.currentThread().getName() + " result=" + result);
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} catch (Exception e) {
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e.printStackTrace();
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}
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}).start();
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}
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}

‎Cache/src/CacheUsage4.java‎

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import java.util.HashMap;
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import java.util.Map;
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import java.util.concurrent.ConcurrentHashMap;
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/**
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* (使用)ConcurrentHashMap >>>> 问题:出现线程重复计算的问题
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*
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* @Author: zzStar
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* @Date: 10-13-2020 13:03
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*/
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public class CacheUsage4<A, V> implements Computable<A, V> {
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private final Map<A, V> cache = new ConcurrentHashMap<>();
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private final Computable<A, V> computable;
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public CacheUsage4(Computable<A, V> computable) {
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this.computable = computable;
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}
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@Override
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public V compute(A arg) throws Exception {
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System.out.println(Thread.currentThread().getName() + " 进入缓存机制");
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V result = cache.get(arg);
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if (result == null) {
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result = computable.compute(arg);
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cache.put(arg, result);
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}
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return result;
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}
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public static void main(String[] args) {
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CacheUsage4<String, Integer> usage3 = new CacheUsage4<>(new ExpensiveFunc());
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new Thread(() -> {
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try {
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Integer result = usage3.compute("5656");
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System.out.println(Thread.currentThread().getName() + " result=" + result);
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} catch (Exception e) {
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e.printStackTrace();
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}
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}).start();
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new Thread(() -> {
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try {
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Integer result = usage3.compute("5656");
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System.out.println(Thread.currentThread().getName() + " result=" + result);
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} catch (Exception e) {
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e.printStackTrace();
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}
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}).start();
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new Thread(() -> {
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try {
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Integer result = usage3.compute("9090");
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System.out.println(Thread.currentThread().getName() + " result=" + result);
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} catch (Exception e) {
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e.printStackTrace();
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}
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}).start();
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}
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}

‎Cache/src/CacheUsage5.java‎

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import java.util.Map;
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import java.util.concurrent.*;
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/**
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* @Description: 利用future避免重复计算 + 缓存过期到期自动失效
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* @Author: zzStar
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* @Date: 2020/10/13 13:45
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*/
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public class CacheUsage5<A, V> implements Computable<A, V> {
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private final Map<A, Future<V>> cache = new ConcurrentHashMap<>();
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private final Computable<A, V> computable;
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public CacheUsage5(Computable<A, V> computable) {
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this.computable = computable;
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}
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@Override
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public V compute(A arg) {
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Future<V> future = cache.get(arg);
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if (future == null) {
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Callable<V> callable = () -> computable.compute(arg);
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FutureTask<V> futureTask = new FutureTask<>(callable);
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//原子组合操作，每一个线程进来都先做一次判断
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future = cache.putIfAbsent(arg, futureTask);
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if (future == null) {
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future = futureTask;
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System.out.println("从FutureTask调用计算函数");
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futureTask.run();
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}
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//计算之前放入缓存
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//cache.put(arg, futureTask);
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}
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V v = null;
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try {
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//计算的时候有可能会出现异常
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v = future.get();
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} catch (InterruptedException | ExecutionException e) {
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System.out.println("出现异常 " + e.getMessage());
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//取消线程任务,发送中断信号
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future.cancel(true);
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}
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//在有结果之前会阻塞
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return v;
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}
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//延迟功能
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private final static ScheduledExecutorService service = Executors.newScheduledThreadPool(5);
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//缓存过期功能,重载
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public V compute(A arg, long expire) {
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//超时时间>0
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if (expire > 0) {
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service.schedule(() -> {
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//如果还在计算,则直接取消任务
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Future<V> vFuture = cache.get(arg);
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if (vFuture != null) {
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if (!vFuture.isDone()) {
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vFuture.cancel(true);
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}
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}
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cache.remove(arg);
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System.out.println("过期时间到了,清除缓存:" + arg);
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}, expire,TimeUnit.MILLISECONDS);
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}
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service.shutdown();
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return compute(arg);
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}
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//把缓存的时间设置为随机，过期时间不设置为统一，避免缓存雪崩
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public V computeRandomExpire(A arg) {
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long expire = (long) (Math.random() * 10000);
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return compute(arg, expire);
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}
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public static void main(String[] args) {
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CacheUsage5<String, Integer> usage5 = new CacheUsage5<>(new ExpensiveFunc());
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new Thread(() -> {
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try {
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Integer result = usage5.computeRandomExpire("1222");
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System.out.println(Thread.currentThread().getName() + " result=" + result);
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} catch (Exception e) {
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e.printStackTrace();
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}
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}).start();
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new Thread(() -> {
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try {
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Integer result = usage5.compute("1222");
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System.out.println(Thread.currentThread().getName() + " result=" + result);
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} catch (Exception e) {
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e.printStackTrace();
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}
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}).start();
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new Thread(() -> {
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try {
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Integer result = usage5.compute("1222");
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System.out.println(Thread.currentThread().getName() + " result=" + result);
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} catch (Exception e) {
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e.printStackTrace();
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}
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}).start();
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}
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}

‎Cache/src/CacheUsage5Test.java‎

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import java.text.SimpleDateFormat;
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import java.util.Date;
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import java.util.concurrent.CountDownLatch;
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import java.util.concurrent.ExecutorService;
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import java.util.concurrent.Executors;
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/**
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* 测试CacheUsage5
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*
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* @Author: zzStar
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* @Date: 10-13-2020 14:39
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*/
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public class CacheUsage5Test {
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static CacheUsage5<String, Integer> cache = new CacheUsage5<>(new ExpensiveFunc());
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public static void main(String[] args) throws InterruptedException {
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ExecutorService pool = Executors.newFixedThreadPool(100);
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//实现压测，同一时刻大量请求
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CountDownLatch countDownLatch = new CountDownLatch(1);
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for (int i = 0; i < 100; i++) {
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pool.submit(() -> {
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try {
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System.out.println(Thread.currentThread().getName() + "准备中.....");
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countDownLatch.await();
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System.out.println(Thread.currentThread().getName() + " 放行:" + TimeHolder.get().format(new Date()));
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Integer result = cache.compute("666");
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System.out.println("result=" + result);
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} catch (Exception e) {
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e.printStackTrace();
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}
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});
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}
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Thread.sleep(3000);
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countDownLatch.countDown();
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pool.shutdown();
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}
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}
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class TimeHolder {
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//每个线程需要独享的对象
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private static ThreadLocal<SimpleDateFormat> threadLocal = ThreadLocal.withInitial(() -> new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"));
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public static SimpleDateFormat get() {
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return threadLocal.get();
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}
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}
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‎Cache/src/Computable.java‎

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/**
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* 提高代码复用性 —> 装饰者模式
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* 实现无侵入缓存功能
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*
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* @Author: zzStar
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* @Date: 10-13-2020 12:54
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*/
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public interface Computable<A,V> {
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V compute(A arg) throws Exception;
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}

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