org.springframework.boot
spring-boot-starter-web
org.springframework.boot
spring-boot-starter-test
test
package com.example.springboottest.guava_cache;
import com.google.common.base.MoreObjects;
/***************************************
@author:Alex Wang
@Date:2017/11/18
QQ: 532500648
-
QQ群:463962286
***************************************/
public class Employee
{
private final String name;
private final String dept;
private final String empID;
private final byte[] data = new byte[1024 * 1024];public Employee(String name, String dept, String empID)
{
this.name = name;
this.dept = dept;
this.empID = empID;
}public String getName()
{
return name;
}public String getDept()
{
return dept;
}public String getEmpID()
{
return empID;
}@Override
public String toString()
{
return MoreObjects.toStringHelper(this)
.add("Name", this.getName()).add("Department", getDept())
.add("EmployeeID", this.getEmpID()).toString();
}@Override
protected void finalize() throws Throwable
{
System.out.println("The name " + getName() + " will be GC.");
}
}
package com.example.springboottest.guava_cache;
import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;
import com.google.common.cache.Weigher;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeUnit;
public class _1_CacheLoaderBasicTest {
public static void main(String[] args) throws Exception{
// test1();
// test2();
// test3();
// test4();
test5();
}
/**测试软引用在缓存中被过期
* 需要设置堆内存信息
* -Xms64M -Xmx64M -XX:+PrintGCDetails
* @throws Exception
*/
private static void test5() throws Exception{
LoadingCache cache = CacheBuilder.newBuilder()
.expireAfterWrite(200, TimeUnit.SECONDS)
.softValues()//只能对values 做软引用处理
.build(createCacheLoader2());
int i = 0;
//Employee 内部会有一个1M的数组，所以一个Employee对象 至少占1M空间
//由于软引用在内存快不足的时候会被回收 所以这里运行结果 可以创建很多对象 不止64个
//todo 但是考虑到软引用的性能影响 一般我们在在缓存中设置size来限制缓存所占内存的总大小 而不是使用软引用来
for (; ; ) {
String key = "Alex" + i;
cache.put(key, new Employee(key, key, key));
// cache.get(key);
// System.gc();
System.out.println("The Employee [" + (i++) + "] is store into cache.");
TimeUnit.MILLISECONDS.sleep(200);
}
}
//测试弱引用(weakReference) 在缓存中被过期
public static void test4() throws InterruptedException {
LoadingCache cache = CacheBuilder.newBuilder()
.expireAfterWrite(2, TimeUnit.SECONDS)
.weakValues()
.weakKeys()
.build(createCacheLoader2());
cache.getUnchecked("Alex");
cache.getUnchecked("Guava");
//active method
//Thread Active design pattern
System.gc();
TimeUnit.MILLISECONDS.sleep(100);
//weak：弱引用 每次gc的时候 都会将其回收， 所以这里从缓存中拿不到数据了
System.out.println(cache.getIfPresent("Alex"));
}
//测试Write的expire模式下的缓存存活情况
private static void test3() throws Exception {
LoadingCache cache = CacheBuilder.newBuilder()
//expireAfterWrite,write:包括写(write)和更新(update) 不包括读(read)
.expireAfterWrite(2, TimeUnit.SECONDS)
.build(createCacheLoader2());
cache.getUnchecked("Guava");
TimeUnit.SECONDS.sleep(1);
Employee guava = cache.getIfPresent("Guava");
System.out.println(guava);//1s后guava 此时存活
TimeUnit.MILLISECONDS.sleep(900);
guava = cache.getIfPresent("Guava");
System.out.println(guava);//1.90s guava 此时依然存活
TimeUnit.SECONDS.sleep(1);
guava = cache.getIfPresent("Guava");
System.out.println(guava);//2.99s guava 此时不存活
}
//测试Access的expire模式下的缓存存活情况
private static void test2() throws Exception{
LoadingCache cache = CacheBuilder.newBuilder()
//expireAfterAccess,access:包括读(read),写(write),改(update),都会续长缓存的存活期
.expireAfterAccess(2, TimeUnit.SECONDS)
.build(createCacheLoader2());
cache.getUnchecked("Alex");
TimeUnit.SECONDS.sleep(3);
Employee alex = cache.getIfPresent("Alex");//睡眠了 3s 此时缓存获取不到数据
System.out.println(alex);
cache.getUnchecked("Guava");
TimeUnit.SECONDS.sleep(1);
Employee employee = cache.getIfPresent("Guava");//此时Guava存在
System.out.println(employee);
TimeUnit.SECONDS.sleep(1);
employee = cache.getIfPresent("Guava");//再次获取Guava 依然存在
System.out.println(employee);
TimeUnit.SECONDS.sleep(1);
employee = cache.getIfPresent("Guava");//再次获取Guava 依然存在
System.out.println(employee);
}
//测试基础用法
public static void test1() throws ExecutionException, InterruptedException {
//创建一个缓存容器对象 其最大容量是3，容器内元素存放30ms就过期
LoadingCache cache = CacheBuilder.newBuilder()
.maximumSize(3)
.expireAfterAccess(30, TimeUnit.MILLISECONDS)
.build(createCacheLoader());
//#################################### 测试30ms时间过期 ####################################
// System.out.println(cache.get("Alex").getName());
// TimeUnit.MILLISECONDS.sleep(31);
// System.out.println(cache.get("Alex").getName());
//测试到达容量之后 LRU过期
//#################################### 测试到达size之后被LRU过期(过期策略:size) ####################################
// System.out.println(cache.get("Alex").getName());
// System.out.println(cache.get("allen").getName());
// System.out.println(cache.get("tom").getName());
// System.out.println(cache.get("amy").getName());//此时Alex被过期调，再拿Alex的话会从DB中拿
// System.out.println(cache.size());
// System.out.println(cache.get("Alex").getName());
// System.out.println();
//#################################### 测试到达weight之后被LRU过期(过期策略:自定义) ####################################
//设置一个称重器 称重的方式是：对象的重量weight = name的长度 + empId的长度 + Dept的长度
Weigher weigher = (key, employee) ->
employee.getName().length() + employee.getEmpID().length() + employee.getDept().length();
//设置缓存重量限制为45
LoadingCache cache2 = CacheBuilder.newBuilder()
.maximumWeight(45)
.concurrencyLevel(1)
.weigher(weigher)
.build(createCacheLoader());
cache2.get("Gavin");//缓存重量：15
cache2.get("Kevin");//缓存重量：30
cache2.get("Allen");//缓存重量：45
cache2.get("Jason");//重量已经达到45，此时Gavin被过期
Employee employee = cache2.getIfPresent("Gavin");//此时再去缓存中拿Gavin 是拿不到的
System.out.println(employee);
//#################################### LoadingCache 的一些api ####################################
// 从LoadingCache中拿数据，如果拿不到，会去从DB中拿，
// cache.get("aa");
// 与get()方法的区别是这里不需要显式捕获异常
// cache.getUnchecked("aa");
// 从缓存中拿key对应的数据，如果缓存中没有 就返回null，不会去从DB中拿
// cache.getIfPresent("aa");
}
private static CacheLoader createCacheLoader() {
return new CacheLoader() {
@Override
public Employee load(String key) throws Exception {
// 这里要注意：load的时候不能返回空， 那返回空了怎么办？很有可能命中不了
// if (key.equals("aa")) return null;
System.out.println("从数据库中拿数据： " + key);
return new Employee(key, key, key);
}
};
}
private static CacheLoader createCacheLoader2() {
//也可以使用from()来构建缓存
return CacheLoader.from(key -> new Employee(key, key, key));
}
}