一、内存调优
1. 什么是内存泄漏
（1）内存溢出和内存泄漏
2. 监控Java内存的常用工具
（1）Top命令
（2）VisualVM
（3）Arthas
（4）Prometheus + Grafana
（5）堆内存状况的对比
3. 内存泄漏的常见场景
（1）equals()和hashCode()导致的内存泄漏
package com.itheima.jvmoptimize.leakdemo.demo2;
import org.apache.commons.lang3.builder.EqualsBuilder;
import org.apache.commons.lang3.builder.HashCodeBuilder;
import java.util.Objects;
public class Student {
private String name;
private Integer id;
private byte[] bytes = new byte[1024 * 1024];
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
Student student = (Student) o;
return new EqualsBuilder().append(id, student.id).isEquals();
}
@Override
public int hashCode() {
return new HashCodeBuilder(17, 37).append(id).toHashCode();
}
}（2）内部类引用外部类
package com.itheima.jvmoptimize.leakdemo.demo3;
import java.io.IOException;
import java.util.ArrayList;
public class Outer{
private byte[] bytes = new byte[1024 * 1024]; //外部类持有数据
private static String name = "测试";
class Inner{
private String name;
public Inner() {
this.name = Outer.name;
}
}
public static void main(String[] args) throws IOException, InterruptedException {
// System.in.read();
int count = 0;
ArrayList<Inner> inners = new ArrayList<>();
while (true){
if(count++ % 100 == 0){
Thread.sleep(10);
}
inners.add(new Outer().new Inner());
}
}
}package com.itheima.jvmoptimize.leakdemo.demo4;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
public class Outer {
private byte[] bytes = new byte[1024 * 1024 * 10];
public List<String> newList() {
List<String> list = new ArrayList<String>() {{
add("1");
add("2");
}};
return list;
}
public static void main(String[] args) throws IOException {
System.in.read();
int count = 0;
ArrayList<Object> objects = new ArrayList<>();
while (true){
System.out.println(++count);
objects.add(new Outer().newList());
}
}
}
package com.itheima.jvmoptimize.leakdemo.demo3;
import java.io.IOException;
import java.util.ArrayList;
public class Outer{
private byte[] bytes = new byte[1024 * 1024]; //外部类持有数据
private static String name = "测试";
static class Inner{
private String name;
public Inner() {
this.name = Outer.name;
}
}
public static void main(String[] args) throws IOException, InterruptedException {
// System.in.read();
int count = 0;
ArrayList<Inner> inners = new ArrayList<>();
while (true){
if(count++ % 100 == 0){
Thread.sleep(10);
}
inners.add(new Inner());
}
}
}package com.itheima.jvmoptimize.leakdemo.demo4;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
public class Outer {
private byte[] bytes = new byte[1024 * 1024 * 10];
public static List<String> newList() {
List<String> list = new ArrayList<String>() {{
add("1");
add("2");
}};
return list;
}
public static void main(String[] args) throws IOException {
System.in.read();
int count = 0;
ArrayList<Object> objects = new ArrayList<>();
while (true){
System.out.println(++count);
objects.add(newList());
}
}
}（3）ThreadLocal的使用
package com.itheima.jvmoptimize.leakdemo.demo5;
import java.util.concurrent.*;
public class Demo5 {
public static ThreadLocal<Object> threadLocal = new ThreadLocal<>();
public static void main(String[] args) throws InterruptedException {
ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(Integer.MAX_VALUE, Integer.MAX_VALUE,
0, TimeUnit.DAYS, new SynchronousQueue<>());
int count = 0;
while (true) {
System.out.println(++count);
threadPoolExecutor.execute(() -> {
threadLocal.set(new byte[1024 * 1024]);
// threadLocal.remove();
});
Thread.sleep(10);
}
}
}（4）String的intern方法
package com.itheima.jvmoptimize.leakdemo.demo6;
import org.apache.commons.lang3.RandomStringUtils;
import java.util.ArrayList;
import java.util.List;
public class Demo6 {
public static void main(String[] args) {
while (true){
List<String> list = new ArrayList<String>();
int i = 0;
while (true) {
//String.valueOf(i++).intern(); //JDK1.6 perm gen 不会溢出
list.add(String.valueOf(i++).intern()); //溢出
}
}
}
}（5）通过静态字段保存对象
单例模式 -> 懒加载
package com.itheima.jvmoptimize.leakdemo.demo7;
import org.springframework.context.annotation.Lazy;
import org.springframework.stereotype.Component;
@Lazy //懒加载
@Component
public class TestLazy {
private byte[] bytes = new byte[1024 * 1024 * 1024];
}Spring的Bean中不要长期存放大对象，如果是缓存用于提升性能，尽量设置过期时间
package com.itheima.jvmoptimize.leakdemo.demo7;
import com.github.benmanes.caffeine.cache.Cache;
import com.github.benmanes.caffeine.cache.Caffeine;
import java.time.Duration;
public class CaffineDemo {
public static void main(String[] args) throws InterruptedException {
Cache<Object, Object> build = Caffeine.newBuilder()
//设置100ms之后就过期
.expireAfterWrite(Duration.ofMillis(100))
.build();
int count = 0;
while (true){
build.put(count++,new byte[1024 * 1024 * 10]);
Thread.sleep(100L);
}
}
}（6）资源没有正常关闭
package com.itheima.jvmoptimize.leakdemo.demo1;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.net.URLConnection;
import java.sql.*;
//-Xmx50m -Xms50m
public class Demo1 {
// JDBC driver name and database URL
static final String JDBC_DRIVER = "com.mysql.cj.jdbc.Driver";
static final String DB_URL = "jdbc:mysql:///bank1";
// Database credentials
static final String USER = "root";
static final String PASS = "123456";
public static void leak() throws SQLException {
//Connection conn = null;
Statement stmt = null;
Connection conn = DriverManager.getConnection(DB_URL, USER, PASS);
// executes a valid query
stmt = conn.createStatement();
String sql;
sql = "SELECT id, account_name FROM account_info";
ResultSet rs = stmt.executeQuery(sql);
//STEP 4: Extract data from result set
while (rs.next()) {
//Retrieve by column name
int id = rs.getInt("id");
String name = rs.getString("account_name");
//Display values
System.out.print("ID: " + id);
System.out.print(", Name: " + name + "\n");
}
}
public static void main(String[] args) throws InterruptedException, SQLException {
while (true) {
leak();
}
}
}
4. 内存泄漏的解决方案
（1）内存快照
package com.itheima.jvmoptimize.matdemo;
import org.openjdk.jol.info.ClassLayout;
import java.util.ArrayList;
import java.util.List;
//-XX:+HeapDumpBeforeFullGC -XX:HeapDumpPath=D:/jvm/dump/mattest.hprof
public class HeapDemo {
public static void main(String[] args) {
TestClass a1 = new TestClass();
TestClass a2 = new TestClass();
TestClass a3 = new TestClass();
String s1 = "itheima1";
String s2 = "itheima2";
String s3 = "itheima3";
a1.list.add(s1);
a2.list.add(s1);
a2.list.add(s2);
a3.list.add(s3);
//System.out.print(ClassLayout.parseClass(TestClass.class).toPrintable());
s1 = null;
s2 = null;
s3 = null;
System.gc();
}
}
class TestClass {
public List<String> list = new ArrayList<>(10);
}
或
（2）修复问题
总结：
二、GC调优
1. GC调优的核心指标
（1）垃圾回收吞吐量
（2）延迟
（3）内存使用量
2. GC调优的方法
（1）发现问题
（2）常见的GC模式
（3）解决GC问题的手段
（3-1）优化基础JVM参数
（3-2）减少对象产生
（3-3）更换垃圾回收器
（3-4）优化垃圾回收器参数
三、性能调优
1. 性能调优解决的问题
2. 性能调优的方法
（1）线程转储的查看方式
（2）请求单个服务处理时间特别长
（3）程序启动之后运行正常，但是在运行一段时间之后无法处理任何的请求（内存和GC正常）
3. JMH基准测试框架
测试代码：
package org.sample;
import org.openjdk.jmh.annotations.*;
import org.openjdk.jmh.results.format.ResultFormatType;
import org.openjdk.jmh.runner.Runner;
import org.openjdk.jmh.runner.RunnerException;
import org.openjdk.jmh.runner.options.Options;
import org.openjdk.jmh.runner.options.OptionsBuilder;
import java.text.SimpleDateFormat;
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.util.Date;
import java.util.concurrent.TimeUnit;
//执行5轮预热，每次持续1秒
@Warmup(iterations = 5, time = 1, timeUnit = TimeUnit.SECONDS)
//执行一次测试
@Fork(value = 1, jvmArgsAppend = {"-Xms1g", "-Xmx1g"})
//显示平均时间，单位纳秒
@BenchmarkMode(Mode.AverageTime)
// 指定显示结果单位
@OutputTimeUnit(TimeUnit.NANOSECONDS)
// 变量共享范围
@State(Scope.Benchmark)
public class HelloWorldBench {
@Benchmark
public int test1() {
int i = 0;
i++;
return i;
}
public static void main(String[] args) throws RunnerException {
Options opt = new OptionsBuilder()
.include(HelloWorldBench.class.getSimpleName())
.resultFormat(ResultFormatType.JSON)
.forks(1)
.build();
new Runner(opt).run();
}
}如果不将i返回，JIT会直接将这段代码去掉，因为它认为你不会使用i那么我们对i进行的任何处理都是没有意义的，这种代码无法执行的现象称之为死代码
我们可以将i返回，或者添加黑洞来消费这些变量，让JIT无法消除这些代码:
package org.sample;
import org.openjdk.jmh.annotations.*;
import org.openjdk.jmh.results.format.ResultFormatType;
import org.openjdk.jmh.runner.Runner;
import org.openjdk.jmh.runner.RunnerException;
import org.openjdk.jmh.runner.options.Options;
import org.openjdk.jmh.runner.options.OptionsBuilder;
import java.text.SimpleDateFormat;
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.util.Date;
import java.util.concurrent.TimeUnit;
//执行5轮预热，每次持续1秒
@Warmup(iterations = 5, time = 1, timeUnit = TimeUnit.SECONDS)
//执行一次测试
@Fork(value = 1, jvmArgsAppend = {"-Xms1g", "-Xmx1g"})
//显示平均时间，单位纳秒
@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
@State(Scope.Thread)
public class DateBench {
private static String sDateFormatString = "yyyy-MM-dd HH:mm:ss";
private Date date = new Date();
private LocalDateTime localDateTime = LocalDateTime.now();
private static ThreadLocal<SimpleDateFormat> simpleDateFormatThreadLocal = new ThreadLocal();
private static final DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
@Setup
public void setUp() {
SimpleDateFormat sdf = new SimpleDateFormat(sDateFormatString);
simpleDateFormatThreadLocal.set(sdf);
}
@Benchmark
public String date() {
SimpleDateFormat simpleDateFormat = new SimpleDateFormat(sDateFormatString);
return simpleDateFormat.format(date);
}
@Benchmark
public String localDateTime() {
return localDateTime.format(formatter);
}
@Benchmark
public String localDateTimeNotSave() {
return localDateTime.format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));
}
@Benchmark
public String dateThreadLocal() {
return simpleDateFormatThreadLocal.get().format(date);
}
public static void main(String[] args) throws RunnerException {
Options opt = new OptionsBuilder()
.include(DateBench.class.getSimpleName())
.resultFormat(ResultFormatType.JSON)
.forks(1)
.build();
new Runner(opt).run();
}
}
package com.itheima.jvmoptimize.performance.practice.controller;
import com.itheima.jvmoptimize.performance.practice.entity.User;
import com.itheima.jvmoptimize.performance.practice.entity.UserDetails;
import com.itheima.jvmoptimize.performance.practice.service.UserService;
import com.itheima.jvmoptimize.performance.practice.vo.UserVO;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import java.text.SimpleDateFormat;
import java.time.format.DateTimeFormatter;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
@RestController
@RequestMapping("/puser")
public class UserController {
@Autowired
private UserService userService;
private final DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
//初始代码
public List<UserVO> user1(){
//1.从数据库获取前端需要的详情数据
List<UserDetails> userDetails = userService.getUserDetails();
//2.获取缓存中的用户数据
List<User> users = userService.getUsers();
SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
//3.遍历详情集合，从缓存中获取用户名，生成VO进行填充
ArrayList<UserVO> userVOS = new ArrayList<>();
for (UserDetails userDetail : userDetails) {
UserVO userVO = new UserVO();
//可以使用BeanUtils对象拷贝
userVO.setId(userDetail.getId());
userVO.setRegister(simpleDateFormat.format(userDetail.getRegister2()));
//填充name
for (User user : users) {
if(user.getId().equals(userDetail.getId())){
userVO.setName(user.getName());
}
}
//加入集合
userVOS.add(userVO);
}
return userVOS;
}
//使用HasmMap存放用户名字
public List<UserVO> user2(){
//1.从数据库获取前端需要的详情数据
List<UserDetails> userDetails = userService.getUserDetails();
//2.获取缓存中的用户数据
List<User> users = userService.getUsers();
//将list转换成hashmap
HashMap<Long, User> map = new HashMap<>();
for (User user : users) {
map.put(user.getId(),user);
}
SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
//3.遍历详情集合，从缓存中获取用户名，生成VO进行填充
ArrayList<UserVO> userVOS = new ArrayList<>();
for (UserDetails userDetail : userDetails) {
UserVO userVO = new UserVO();
//可以使用BeanUtils对象拷贝
userVO.setId(userDetail.getId());
userVO.setRegister(simpleDateFormat.format(userDetail.getRegister2()));
//填充name
userVO.setName(map.get(userDetail.getId()).getName());
//加入集合
userVOS.add(userVO);
}
return userVOS;
}
//优化日期格式化
public List<UserVO> user3(){
//1.从数据库获取前端需要的详情数据
List<UserDetails> userDetails = userService.getUserDetails();
//2.获取缓存中的用户数据
List<User> users = userService.getUsers();
//将list转换成hashmap
HashMap<Long, User> map = new HashMap<>();
for (User user : users) {
map.put(user.getId(),user);
}
//3.遍历详情集合，从缓存中获取用户名，生成VO进行填充
ArrayList<UserVO> userVOS = new ArrayList<>();
for (UserDetails userDetail : userDetails) {
UserVO userVO = new UserVO();
//可以使用BeanUtils对象拷贝
userVO.setId(userDetail.getId());
userVO.setRegister(userDetail.getRegister().format(formatter));
//填充name
userVO.setName(map.get(userDetail.getId()).getName());
//加入集合
userVOS.add(userVO);
}
return userVOS;
}
@GetMapping
//使用stream流改写for循环
public List<UserVO> user4(){
//1.从数据库获取前端需要的详情数据
List<UserDetails> userDetails = userService.getUserDetails();
//2.获取缓存中的用户数据
List<User> users = userService.getUsers();
//将list转换成hashmap
Map<Long, User> map = users.stream().collect(Collectors.toMap(User::getId, o -> o));
//3.遍历详情集合，从缓存中获取用户名，生成VO进行填充
return userDetails.stream().map(userDetail -> {
UserVO userVO = new UserVO();
//可以使用BeanUtils对象拷贝
userVO.setId(userDetail.getId());
userVO.setRegister(userDetail.getRegister().format(formatter));
//填充name
userVO.setName(map.get(userDetail.getId()).getName());
return userVO;
}).collect(Collectors.toList());
}
//使用并行流优化性能
public List<UserVO> user5(){
//1.从数据库获取前端需要的详情数据
List<UserDetails> userDetails = userService.getUserDetails();
//2.获取缓存中的用户数据
List<User> users = userService.getUsers();
//将list转换成hashmap
Map<Long, User> map = users.parallelStream().collect(Collectors.toMap(User::getId, o -> o));
//3.遍历详情集合，从缓存中获取用户名，生成VO进行填充
return userDetails.parallelStream().map(userDetail -> {
UserVO userVO = new UserVO();
//可以使用BeanUtils对象拷贝
userVO.setId(userDetail.getId());
userVO.setRegister(userDetail.getRegister().format(formatter));
//填充name
userVO.setName(map.get(userDetail.getId()).getName());
return userVO;
}).collect(Collectors.toList());
}
}在SpringBoot项目中整合JMH:
1、pom文件中添加依赖:
<dependency>
<groupId>org.openjdk.jmh</groupId>
<artifactId>jmh-core</artifactId>
<version>${jmh.version}</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.openjdk.jmh</groupId>
<artifactId>jmh-generator-annprocess</artifactId>
<version>${jmh.version}</version>
<scope>test</scope>
</dependency><properties>
<java.version>8</java.version>
<jmh.version>1.37</jmh.version>
</properties>2、测试类中编写:
package com.itheima.jvmoptimize;
import com.itheima.jvmoptimize.performance.practice.controller.UserController;
import org.junit.jupiter.api.Test;
import org.openjdk.jmh.annotations.*;
import org.openjdk.jmh.infra.Blackhole;
import org.openjdk.jmh.results.format.ResultFormatType;
import org.openjdk.jmh.runner.Runner;
import org.openjdk.jmh.runner.RunnerException;
import org.openjdk.jmh.runner.options.OptionsBuilder;
import org.springframework.boot.SpringApplication;
import org.springframework.context.ApplicationContext;
import java.io.IOException;
import java.util.concurrent.TimeUnit;
//执行5轮预热，每次持续1秒
@Warmup(iterations = 5, time = 1, timeUnit = TimeUnit.SECONDS)
//执行一次测试
@Fork(value = 1, jvmArgsAppend = {"-Xms1g", "-Xmx1g"})
//显示平均时间，单位纳秒
@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.MILLISECONDS)
@State(Scope.Benchmark)
public class PracticeBenchmarkTest {
private UserController userController;
private ApplicationContext context;
//初始化将springboot容器启动 端口号随机
@Setup
public void setup() {
this.context = new SpringApplication(JvmOptimizeApplication.class).run();
userController = this.context.getBean(UserController.class);
}
//启动这个测试用例进行测试
@Test
public void executeJmhRunner() throws RunnerException, IOException {
new Runner(new OptionsBuilder()
.shouldDoGC(true)
.forks(0)
.resultFormat(ResultFormatType.JSON)
.shouldFailOnError(true)
.build()).run();
}
//用黑洞消费数据，避免JIT消除代码
@Benchmark
public void test1(final Blackhole bh) {
bh.consume(userController.user1());
}
@Benchmark
public void test2(final Blackhole bh) {
bh.consume(userController.user2());
}
@Benchmark
public void test3(final Blackhole bh) {
bh.consume(userController.user3());
}
@Benchmark
public void test4(final Blackhole bh) {
bh.consume(userController.user4());
}
@Benchmark
public void test5(final Blackhole bh) {
bh.consume(userController.user5());
}
}
