Google Guava学习（9）-Guava Cache缓存工具（二）

1. 功能：本地缓存

2. 代码：两个类，一个测试类，一个缓存类

package com.example.google.guava.demo.cache;import com.example.google.guava.demo.model.Department;import com.google.common.cache.*;import java.text.SimpleDateFormat;import java.util.Date;import java.util.concurrent.ExecutionException;/** * <p> * <code>LoadingCacheTest</code> * </p> * Description:guava缓存工具,类似于使用java.util.concurrent.ConcurrentHashMap做缓存 * * @author Mcchu * @date 2017/10/20 9:18 */public class LoadingCacheTest {    private static SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");    private Department getDept(String id) throws ExecutionException {        LoadingCache<String, Department> deptCache = LoadingCacheUtil.getLoadingCache();        System.out.println("此缓存累积统计数据的当前快照："+deptCache.stats());        System.out.println("缓存size：" + deptCache.size());        return deptCache.get( id );    }    public static void main(String[] args) throws ExecutionException{        LoadingCacheTest cacheTest = new LoadingCacheTest();        try {            // 1.第一次访问部门，会调用getDepartmentById()方法            System.out.println( dateFormat.format( new Date() ) );            String deptName1 = cacheTest.getDept("102").getDepartmentName();            System.out.println("第一次访问："+deptName1);            // 线程停滞一段时间过后，测试缓存是否存在            Thread.sleep(10000); // 当前设置缓存写入后5s过期，如果线程停滞10s，需要重新读取数据源            // 2.第二次访问，将不再调用getDepartmentById()方法，而是去缓存获取            System.out.println( dateFormat.format( new Date() ) );            String deptName2 = cacheTest.getDept("102").getDepartmentName();            System.out.println("第二次访问："+deptName2);        }catch (InterruptedException e){            e.printStackTrace();        }    }}

package com.example.google.guava.demo.cache;import com.example.google.guava.demo.model.Department;import com.google.common.cache.CacheBuilder;import com.google.common.cache.CacheLoader;import com.google.common.cache.LoadingCache;import java.util.ArrayList;import java.util.List;import java.util.concurrent.TimeUnit;/** * <p> * <code>LoadingCacheUtil</code> * </p> * Description: * * @author Mcchu * @date 2017/10/20 15:04 */public class LoadingCacheUtil {    private static LoadingCache<String, Department> departmentCache;    static {        CacheLoader<String,Department> deptCacheLoader = new CacheLoader<String, Department>() {            @Override            public Department load(String key) throws Exception {                return getDepartmentById( key );            }        };        departmentCache = CacheBuilder.newBuilder()                .maximumSize(100)                .expireAfterWrite(5L, TimeUnit.SECONDS)  //设置写入5s后过期                .build(deptCacheLoader);    }    public static LoadingCache<String, Department> getLoadingCache() {        return departmentCache;    }    /**     * 部门假数据（实际来源可能是数据库或远程接口）     * @return 部门列表     */    private static Department getDepartmentById(String id ){        System.out.println("访问数据源");        List<Department> departmentList = new ArrayList<>();        Department department1 = new Department("101","采购部","1");        Department department2 = new Department("102","财务部","1");        Department department3 = new Department("103","信管部","1");        Department department4 = new Department("104","外贸部","1");        departmentList.add(department1);        departmentList.add(department2);        departmentList.add(department3);        departmentList.add(department4);        for ( Department department:departmentList ){            String deptId = department.getDepartmentId();            if ( id.equals(deptId) ){                return department;            }        }        return null;    }}

3. 测试结果：

① 当线程停滞小于5s时结果

2017-10-20 15:32:18此缓存累积统计数据的当前快照：CacheStats{hitCount=0, missCount=0, loadSuccessCount=0, loadExceptionCount=0, totalLoadTime=0, evictionCount=0}缓存size：0访问数据源第一次访问：财务部2017-10-20 15:32:22此缓存累积统计数据的当前快照：CacheStats{hitCount=0, missCount=0, loadSuccessCount=0, loadExceptionCount=0, totalLoadTime=0, evictionCount=0}缓存size：1第二次访问：财务部

② 当线程停滞大于5s时结果

2017-10-20 15:33:14此缓存累积统计数据的当前快照：CacheStats{hitCount=0, missCount=0, loadSuccessCount=0, loadExceptionCount=0, totalLoadTime=0, evictionCount=0}缓存size：0访问数据源第一次访问：财务部2017-10-20 15:33:24此缓存累积统计数据的当前快照：CacheStats{hitCount=0, missCount=0, loadSuccessCount=0, loadExceptionCount=0, totalLoadTime=0, evictionCount=0}缓存size：1访问数据源第二次访问：财务部

可以发现当停滞时间大于5s时需要重新获取数据源，说明缓存设置是生效的。

附录：

参考：

https://www.concretepage.com/google-api/google-guava-cache-example-using-loadingcache-cachebuilder-and-cacheloader