Guava------------Cache使用方法

简单从这几个方面描述一下如何使用Cache，对Cache的各种原理介绍此处不涉及.

1.使用场景

2.如何使用Cache

3.创建方式

4. 如何和Spring搭配使用

+------------------------------------------------------分割线-------------------------------------------------------+

1. Cache的使用场景

一般而言，对于那些频繁需要查询比对的热点数据，我们采用使用缓存，对于数据量较小的，几条，几十条数据，而且需要加缓存的接口较少，这时候我们会采用Cache,建议使用Google提供的guava Cache，它简单易用的同时，性能也好. 而且线程安全（原因看源码） .对于那些较大数据量的，或者需要加缓存的接口较多的项目，可以去考虑Redis，memcached等等

2. 如何使用Cache

和Map的使用方式差不多，也可以和Spring结合，使用@Cacheable注解使用.

3. 创建方式

1. Cache Callable

2. LoadingCache

方式一：

 package info.sanaulla.cache;

 import com.google.common.cache.Cache;
 import com.google.common.cache.CacheBuilder;
 import org.junit.Test;

 import java.util.concurrent.Callable;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.TimeUnit;

 /**
  * *********************************************************
  * <p/>
  * Author:     XiJun.Gong
  * Date:       2016-08-17 16:59
  * Version:    default 1.0.0
  * Class description：
  * <p/>
  * *********************************************************
  */
 public class CacheDemo {
     private static Cache<Object, Object> cache = CacheBuilder.newBuilder()
             .maximumSize(100).expireAfterWrite(24, TimeUnit.HOURS)
             .recordStats()
             .build();

     public static Object get(Object key) throws ExecutionException {

         Object var = cache.get(key, new Callable<Object>() {
             @Override
             public Object call() throws Exception {
                 System.out.println("如果没有值,就执行其他方式去获取值");
                 String var = "Google.com.sg";
                 return var;
             }
         });
         return var;
     }

     public static void put(Object key, Object value) {
         cache.put(key, value);
     }

     class Person {
         private String name;
         private Integer age;

         public Person() {
         }

         public Person(String name, Integer age) {
             this.name = name;
             this.age = age;
         }

         public String getName() {
             return name;
         }

         public void setName(String name) {
             this.name = name;
         }

         public Integer getAge() {
             return age;
         }

         public void setAge(Integer age) {
             this.age = age;
         }

         @Override
         public String toString() {
             return "Person{" +
                     "名字='" + name + '\'' +
                     ", 年纪=" + age +
                     '}';
         }
     }

     @Test
     public void CacheTest() throws ExecutionException {

         Person person = new Person();
         person.setAge(11);
         person.setName("tSun");
         System.out.println(CacheDemo.get("man"));
         CacheDemo.put("man", new Person("hopg", 123));
         System.out.println(CacheDemo.get("man"));
         System.out.println(CacheDemo.get("man"));

         System.out.println(CacheDemo.get("person").toString());
         CacheDemo.put("person", person);
         System.out.println(CacheDemo.get("person").toString());
         System.out.println(CacheDemo.get("person").toString());

         System.out.println(CacheDemo.get("woman"));
         CacheDemo.put("women", new Person("google", 666));
         System.out.println(CacheDemo.get("woman"));
         System.out.println(CacheDemo.get("woman"));
         System.out.println(CacheDemo.get("man"));
     }
 }

结果：

 如果没有值,就执行其他方式去获取值
 Google.com.sg
 Person{名字='hopg', 年纪=123}
 Person{名字='hopg', 年纪=123}
 如果没有值,就执行其他方式去获取值
 Google.com.sg
 Person{名字='tSun', 年纪=11}
 Person{名字='tSun', 年纪=11}
 如果没有值,就执行其他方式去获取值
 Google.com.sg
 Google.com.sg
 Google.com.sg
 Person{名字='hopg', 年纪=123}

方式二：

 package info.sanaulla.cache;

 import com.google.common.cache.CacheBuilder;
 import com.google.common.cache.CacheLoader;
 import com.google.common.cache.LoadingCache;
 import org.junit.Test;

 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.TimeUnit;

 /**
  * *********************************************************
  * <p/>
  * Author:     XiJun.Gong
  * Date:       2016-08-17 15:00
  * Version:    default 1.0.0
  * Class description：
  * <p>Cache Demo</p>
  * <p/>
  * *********************************************************
  */
 public class CacheUtil {

     private static LoadingCache<Object, Object> cache = CacheBuilder.newBuilder()
             .maximumSize(2)
             .expireAfterAccess(24, TimeUnit.HOURS)
             .recordStats()
             .build(new CacheLoader<Object, Object>() {

                 @Override
                 public Object load(Object key) throws Exception {
                     return key;
                 }
             });

     public static Object get(Object key) throws ExecutionException {
         Object var = cache.get(key);

         if (var.equals(key)) {

             System.out.println("执行其他操作,查询该值");
             /**执行其他操作，获取值**/
             Object object = "Google.com.hk";
             put(key, object);
         } else {
             System.out.println("从Cache中取值....");
         }
         return cache.get(key);
     }

     public static void put(Object key, Object value) {
         cache.put(key, value);
     }

     class Person {
         private String name;
         private Integer age;

         public Person() {
         }

         public Person(String name, Integer age) {
             this.name = name;
             this.age = age;
         }

         public String getName() {
             return name;
         }

         public void setName(String name) {
             this.name = name;
         }

         public Integer getAge() {
             return age;
         }

         public void setAge(Integer age) {
             this.age = age;
         }

         @Override
         public String toString() {
             return "Person{" +
                     "名字='" + name + '\'' +
                     ", 年纪=" + age +
                     '}';
         }
     }

     @Test
     public void TestCache() throws ExecutionException {

         Person person = new Person();
         person.setAge(11);
         person.setName("tSun");
         System.out.println(CacheUtil.get("man"));
         CacheUtil.put("man", new Person("hopg", 123));
         System.out.println(CacheUtil.get("man"));
         System.out.println(CacheUtil.get("man"));

         System.out.println(CacheUtil.get("person").toString());
         CacheUtil.put("person", person);
         System.out.println(CacheUtil.get("person").toString());
         System.out.println(CacheUtil.get("person").toString());

         System.out.println(CacheUtil.get("woman"));
         CacheUtil.put("women", new Person("google", 666));
         System.out.println(CacheUtil.get("woman"));
         System.out.println(CacheUtil.get("woman"));
         System.out.println(CacheUtil.get("man"));
     }
 }

结果：

 执行其他操作,查询该值
 Google.com.hk
 从Cache中取值....
 Person{名字='hopg', 年纪=123}
 从Cache中取值....
 Person{名字='hopg', 年纪=123}
 执行其他操作,查询该值
 Google.com.hk
 从Cache中取值....
 Person{名字='tSun', 年纪=11}
 从Cache中取值....
 Person{名字='tSun', 年纪=11}
 执行其他操作,查询该值
 Google.com.hk
 从Cache中取值....
 Google.com.hk
 从Cache中取值....
 Google.com.hk
 执行其他操作,查询该值
 Google.com.hk

4. 如何和Spring结合使用

因为我们需要使用Spring的注解，所以需要重写Spring的一些接口，然后进行自定义.

4.1 首先简单了解一下@Cacheable,@CachePut,@CacheEvit

对于cache和数据操作进行一个功能对应，如下图.

　　　　  cache　　　　　       　sql

　　　　 Cacheable   　　　　--save/insert

关于Cacheable的简单说明：

@Cacheable注解，如果是类被注解，那么该类所有的方法下,如果在查询时，会先去查询缓存，没有的话，再去调用方法查询，

并且方法的返回值都会被缓存，如果是方法被注解，那么查询的时候，也会遵从先缓存，然后在方法，并且该方法的返回值都会被缓存.

CachePut    　　　　--update/Insert

CacheEvit   　　　　 --remove/delete

4.2 首先我们需要实现接口Spring的BeanAware接口，以及InitializingBean接口,并实现FactoryBean接口，还有实现Spring的

AbstractTransactionSupportingCacheManager抽象类

过程大致如下：

1. 实现Cache接口

 import com.google.common.cache.CacheBuilder;
 import com.google.common.cache.CacheBuilderSpec;
 import org.springframework.cache.Cache;
 import org.springframework.cache.support.SimpleValueWrapper;

 import java.io.Serializable;
 import java.util.concurrent.TimeUnit;

 import static com.google.common.base.Preconditions.checkNotNull;

 /**
  * *********************************************************
  * <p/>
  * Author:     XiJun.Gong
  * Date:       2016-08-22 15:47
  * Version:    default 1.0.0
  * Class description：
  * <p/>
  * *********************************************************
  */
 public class GuavaCache implements Cache {

     private static final Object NULL_HOLDER = new NullHolder();

     private final String name;

     private final com.google.common.cache.Cache<Object, Object> store;

     private final boolean allowNullValues;

     /**
      * Create a new GuavaCache with the specified name.
      *
      * @param name the name of the cache
      */
     public GuavaCache(String name) {
         this(name, CacheBuilder.newBuilder(), true);
     }

     /**
      * Create a new GuavaCache with the specified name.
      *
      * @param name            the name of the cache
      * @param allowNullValues whether to accept and convert null values for this cache
      */
     public GuavaCache(String name, boolean allowNullValues) {
         this(name, CacheBuilder.newBuilder(), allowNullValues);
     }

     /**
      * Create a new GuavaCache using the specified name and {@link com.google.common.cache.CacheBuilderSpec specification}
      *
      * @param name the name of the cache
      * @param spec the cache builder specification to use to build he cache
      */
     public GuavaCache(String name, CacheBuilderSpec spec, boolean allowNullValues) {
         this(name, CacheBuilder.from(spec), allowNullValues);
     }

     /**
      * Create a new GuavaCache using the specified name and {@link CacheBuilderSpec specification}
      *
      * @param name    the name of the cache
      * @param builder the cache builder to use to build the cache
      */
     public GuavaCache(String name, CacheBuilder<Object, Object> builder, boolean allowNullValues) {
         this.name = checkNotNull(name, "name is required");
         this.allowNullValues = allowNullValues;
         this.store = builder.maximumSize(CacheConstant.defaultCacheSize).
                 expireAfterWrite(CacheConstant.defaultCacheExpire, TimeUnit.MINUTES).
                 build();
     }

     @Override
     public String getName() {
         return this.name;
     }

     @Override
     public com.google.common.cache.Cache<Object, Object> getNativeCache() {
         return this.store;
     }

     @Override
     public ValueWrapper get(Object key) {
         Object value = this.store.getIfPresent(key);
         return (value != null ? new SimpleValueWrapper(fromStoreValue(value)) : null);
     }

     @Override
     public void put(Object key, Object value) {
         this.store.put(key, value);
     }

     /**
      * remove the key of object
      *
      * @param key
      */
     @Override
     public void evict(Object key) {
         this.store.invalidate(key);
     }

     /**
      * clear all
      */
     @Override
     public void clear() {
         this.store.invalidateAll();
     }

     /**
      * Convert the given value from the internal store to a user value
      * returned from the get method (adapting {@code null}).
      *
      * @param storeValue the store value
      * @return the value to return to the user
      */
     protected Object fromStoreValue(Object storeValue) {
         if (this.allowNullValues && storeValue == NULL_HOLDER) {
             return null;
         }
         return storeValue;
     }

     /**
      * Convert the given user value, as passed into the put method,
      * to a value in the internal store (adapting {@code null}).
      *
      * @param userValue the given user value
      * @return the value to store
      */
     protected Object toStoreValue(Object userValue) {
         if (this.allowNullValues && userValue == null) {
             return NULL_HOLDER;
         }
         return userValue;
     }

     @SuppressWarnings("serial")
     private static class NullHolder implements Serializable {

     }
 }

2.实现Spring的FactoryBean,BeanAware，InitializingBean接口

 import com.google.common.cache.CacheBuilder;
 import org.springframework.beans.factory.BeanNameAware;
 import org.springframework.beans.factory.FactoryBean;
 import org.springframework.beans.factory.InitializingBean;
 import org.springframework.util.StringUtils;

 /**
  * *********************************************************
  * <p/>
  * Author:     XiJun.Gong
  * Date:       2016-08-22 16:00
  * Version:    default 1.0.0
  * Class description：
  * <p>{@link FactoryBean} for easy configuration of a {@link GuavaCache}.</p>
  * <p/>
  * *********************************************************
  */
 public class GuavaCacheFactoryBean
         implements FactoryBean<GuavaCache>, BeanNameAware, InitializingBean {

     private String name = "";

     private boolean allowNullValues = true;

     private String spec;

     private GuavaCache cache;

     public void setName(String name) {
         this.name = name;
     }

     public void setAllowNullValues(boolean allowNullValues) {
         this.allowNullValues = allowNullValues;
     }

     public void setSpec(String spec) {
         this.spec = spec;
     }

     @Override
     public void setBeanName(String name) {
         if (!StringUtils.hasLength(this.name)) {
             this.name = name;
         }
     }

     @Override
     public void afterPropertiesSet() throws Exception {
         if (StringUtils.hasText(this.spec)) {
             this.cache = new GuavaCache(this.name, CacheBuilder.from(spec), allowNullValues);
         } else {
             this.cache = new GuavaCache(this.name, allowNullValues);
         }
     }

     @Override
     public GuavaCache getObject() throws Exception {
         return this.cache;
     }

     @Override
     public Class<?> getObjectType() {
         return GuavaCache.class;
     }

     @Override
     public boolean isSingleton() {
         return true;
     }

 }

3.实现Spring的Manager类

 import com.google.common.cache.CacheBuilder;
 import com.google.common.cache.CacheLoader;
 import org.springframework.cache.Cache;
 import org.springframework.cache.transaction.AbstractTransactionSupportingCacheManager;
 import org.springframework.util.StringUtils;

 import java.util.Collection;
 import java.util.Collections;
 import java.util.concurrent.TimeUnit;

 /**
  * *********************************************************
  * <p/>
  * Author:     XiJun.Gong
  * Date:       2016-08-22 16:09
  * Version:    default 1.0.0
  * Class description：
  * <p> {@link org.springframework.cache.CacheManager} implementation backed by {@link GuavaCache}.</p>
  * <p/>
  * *********************************************************
  */
 public class GuavaCacheManager extends AbstractTransactionSupportingCacheManager {
     private Collection<GuavaCache> caches;

     private String spec;

     private volatile CacheBuilder<Object, Object> cacheBuilder;

     private boolean allowNullValues = true;

     public GuavaCacheManager() {
     }

     public void setCaches(Collection<GuavaCache> caches) {
         this.caches = caches;
     }

     public void setSpec(String spec) {
         this.spec = spec;
     }

     public String getSpec() {
         return spec;
     }

     public void setAllowNullValues(boolean allowNullValues) {
         this.allowNullValues = allowNullValues;
     }

     public boolean isAllowNullValues() {
         return allowNullValues;
     }

     @Override
     protected Collection<? extends Cache> loadCaches() {
         return (caches != null) ? caches : Collections.<GuavaCache>emptyList();
     }

     @Override
     public Cache getCache(String name) {
         Cache cache = super.getCache(name);
         if (cache == null) {
             // create a new cache
             cache = createGuavaCache(name);

             // add to collection of available caches
             addCache(cache);
         }
         return cache;
     }

     private GuavaCache createGuavaCache(String name) {
         // create GuavaCache
         return new GuavaCache(name, getCacheBuilder(), allowNullValues);
     }

     private CacheBuilder<Object, Object> getCacheBuilder() {
         if (cacheBuilder == null) {
             synchronized (this) {
                 if (cacheBuilder == null) {
                     if (StringUtils.hasText(spec)) {
                         cacheBuilder = CacheBuilder.from(spec);
                     } else {
                         cacheBuilder =CacheBuilder.newBuilder();
                     }

                 }
                 notify();
             }
         }

         return cacheBuilder;
     }

 }

4.3 配置spring配置文件applicationContext.xml

     <!--添加Cache-->
     <!--添加一个注解驱动不要掉-->
     <tx:annotation-driven/>
     <!--使用spring注解去扫描需要加缓存地方的的包-->
     <context:component-scan base-package="com.qunar.data.allinone.bus.testModel">
         <context:exclude-filter type="annotation" expression="org.springframework.context.annotation.Configuration"/>
     </context:component-scan>
     <!-- cache Manager-->
     <bean id="cacheManager" class="com.qunar.data.allinone.bus.cache.GuavaCacheManager">
         <property name="caches">
             <list>
                 <bean class="com.qunar.data.allinone.bus.cache.GuavaCacheFactoryBean" name="msg-cache"/>
             </list>
         </property>
     </bean>
     <!--cache的注解驱动包-->
     <cache:annotation-driven/>

测试即可

 import org.springframework.cache.annotation.Cacheable;
 import org.springframework.stereotype.Component;
 import org.springframework.stereotype.Service;

 /**
  * *********************************************************
  * <p/>
  * Author:     XiJun.Gong
  * Date:       2016-08-22 19:50
  * Version:    default 1.0.0
  * Class description：
  * <p/>
  * *********************************************************
  */
 @Component
 public class TestName {

     @Cacheable(value = "msg-cache")
     public String getName(String con) {
         System.out.println("缓存中没有找到信息");
         return con;
     }
 }

 import com.qunar.data.allinone.bus.testModel.TestName;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.springframework.test.context.ContextConfiguration;
 import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

 import javax.annotation.Resource;

 /**
  * *********************************************************
  * <p/>
  * Author:     XiJun.Gong
  * Date:       2016-08-22 19:30
  * Version:    default 1.0.0
  * Class description：
  * <p/>
  * *********************************************************
  */
 @RunWith(SpringJUnit4ClassRunner.class)
 @ContextConfiguration(value = "classpath:applicationContext.xml")
 public class CacheTest {

     @Resource

     TestName testName;

     @Test
     public void testName() {
         String username = "xijun.gong";
         for (int i = 0; i < 10; i++) {
             System.out.println("++++++++++++++++打印结果:   " + testName.getName(username));
         }
     }
 }

缓存中没有找到信息
++++++++++++++++打印结果:   王小二
++++++++++++++++打印结果:   王小二
++++++++++++++++打印结果:   王小二
++++++++++++++++打印结果:   王小二
++++++++++++++++打印结果:   王小二
++++++++++++++++打印结果:   王小二
++++++++++++++++打印结果:   王小二
++++++++++++++++打印结果:   王小二
++++++++++++++++打印结果:   王小二
++++++++++++++++打印结果:   王小二

5. 扩展

在github上看到一篇关于，对于overflow时候，将数据写入到文件系统的例子，还不错，如果有这方面的需求可以看看.

地址：https://github.com/raphw/guava-cache-overflow-extension