Guava系列：LoadingCache使用方法

目录

​​场景​​

​​demo​​

场景

基于内存LoadingCache缓存数据

demo

package com.nio4444.demo;

import com.google.common.base.MoreObjects;
import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;
import lombok.AllArgsConstructor;

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.TimeUnit;

public class LoadingCacheDemo {
    public static void main(String[] args) {
        LoadingCache cache =
            CacheBuilder.newBuilder()
                .maximumSize(30) //最多缓存30个元素
                .expireAfterAccess(3, TimeUnit.SECONDS) //最多缓存3s
                .build(new CacheLoader<String,Employee>() {
                    @Override
                    public Employee load(String key) throws Exception {
                        return getFromDatabase(key);
                    }
                }) ;

        try{

            System.out.println("-----------sleep before--------------");
            System.out.println("   "+cache.get("103"));
            System.out.println("    "+cache.get("100"));
            System.out.println("    "+cache.get("103"));


            Thread.sleep(3*1000);
            System.out.println("-----------sleep after-------------");
            System.out.println("    "+cache.get("103"));
            System.out.println("    "+cache.get("110"));
        }catch (Exception e){
            e.printStackTrace();
        }

    }


    private static Employee getFromDatabase(String empId){
        Employee e1 = new Employee("Mahesh", "Finance", "100");
        Employee e2 = new Employee("Rohan", "IT", "103");
        Employee e3 = new Employee("Sohan", "Admin", "110");

        Map database = new HashMap();
        database.put("100", e1);
        database.put("103", e2);
        database.put("110", e3);
        System.out.println("@数据库查询" + empId);
        return (Employee) database.get(empId);
    }

}

@AllArgsConstructor
class Employee {
    String name;
    String dept;
    String emplD;

    @Override
    public String toString() {
        return MoreObjects.toStringHelper(Employee.class)
                .add("Name", name)
                .add("Department", dept)
                .add("Emp Id", emplD).toString();
    }

}