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;

    }

}