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;}@Overridepublic 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();}@Overridepublic 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 URLstatic final String JDBC_DRIVER = "com.mysql.cj.jdbc.Driver";static final String DB_URL = "jdbc:mysql:///bank1";// Database credentialsstatic 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 querystmt = conn.createStatement();String sql;sql = "SELECT id, account_name FROM account_info";ResultSet rs = stmt.executeQuery(sql);//STEP 4: Extract data from result setwhile (rs.next()) {//Retrieve by column nameint id = rs.getInt("id");String name = rs.getString("account_name");//Display valuesSystem.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 {@Benchmarkpublic 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");@Setuppublic void setUp() {SimpleDateFormat sdf = new SimpleDateFormat(sDateFormatString);simpleDateFormatThreadLocal.set(sdf);}@Benchmarkpublic String date() {SimpleDateFormat simpleDateFormat = new SimpleDateFormat(sDateFormatString);return simpleDateFormat.format(date);}@Benchmarkpublic String localDateTime() {return localDateTime.format(formatter);}@Benchmarkpublic String localDateTimeNotSave() {return localDateTime.format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));}@Benchmarkpublic 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 {@Autowiredprivate 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namefor (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hashmapHashMap<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nameuserVO.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hashmapHashMap<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nameuserVO.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hashmapMap<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nameuserVO.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hashmapMap<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nameuserVO.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@Setuppublic 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@Testpublic 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@Benchmarkpublic void test1(final Blackhole bh) {bh.consume(userController.user1());}@Benchmarkpublic void test2(final Blackhole bh) {bh.consume(userController.user2());}@Benchmarkpublic void test3(final Blackhole bh) {bh.consume(userController.user3());}@Benchmarkpublic void test4(final Blackhole bh) {bh.consume(userController.user4());}@Benchmarkpublic void test5(final Blackhole bh) {bh.consume(userController.user5());}
}