Java 性能优化

Java 性能优化

Java 性能优化的方向：提高响应速度、减少内存占用

Java性能监控工具

JDK自带性能分析工具

• jps
• jstat
• jinfo
• jmap
• jstack

性能分析工具

• VisualVM
• Memory Analyzer Tool
• Java Profiler

提高响应速度

使用多线程
增加服务器
缓存CDN

减少内存占用

使用IntObjectHashMap 替换Map<Integer,Object>

首先引入依赖

<dependency>
    <groupId>io.netty</groupId>
    <artifactId>netty-all</artifactId>
    <version>4.1.75.Final</version>
</dependency>
<!--openjdk jol-core-->
<dependency>
    <groupId>org.openjdk.jol</groupId>
    <artifactId>jol-cli</artifactId>
    <version>0.16</version>
</dependency>
<dependency>
    <groupId>org.openjdk.jol</groupId>
    <artifactId>jol-core</artifactId>
    <version>0.16</version>
</dependency>

直接上测试代码
首先使用常用的Map<Integer,String>

public class IntObjectHashMapTest {
	private static final Logger LOGGER = LoggerFactory.getLogger(IntObjectHashMapTest.class);


	public static void main(String[] args) throws InterruptedException {
		long freeMemory = Runtime.getRuntime().freeMemory();
		LOGGER.info("before freeMemory {} k Byte", freeMemory);
		int maxSize = 1000;
		HashMap<Integer,String> hashMap = new HashMap<>();
		for (int i = 0; i < maxSize; i++) {
			hashMap.put(i, String.valueOf(i));
		}
		//查看内存占用总大小
		LOGGER.info("hashMap size:[{}] Byte", GraphLayout.parseInstance(hashMap).totalSize());
		freeMemory = Runtime.getRuntime().freeMemory();
		LOGGER.info("after freeMemory {} k Byte", freeMemory);
		TimeUnit.HOURS.sleep(1L);
	}
}

使用 Netty 的 IntObjectHashMap

public class IntObjectHashMapTest {
	private static final Logger LOGGER = LoggerFactory.getLogger(IntObjectHashMapTest.class);


	public static void main(String[] args) throws InterruptedException {
		long freeMemory = Runtime.getRuntime().freeMemory();
		LOGGER.info("before freeMemory {} k Byte", freeMemory);
		int maxSize = 1000;
		IntObjectHashMap<String> hashMap = new IntObjectHashMap<>();
		for (int i = 0; i < maxSize; i++) {
			hashMap.put(i, String.valueOf(i));
		}
		//查看内存占用总大小
		LOGGER.info("hashMap size:[{}] Byte", GraphLayout.parseInstance(hashMap).totalSize());
		freeMemory = Runtime.getRuntime().freeMemory();
		LOGGER.info("after freeMemory {} k Byte", freeMemory);
		TimeUnit.HOURS.sleep(1L);
	}
}

运行上面的代码，通过日志输出，我们可以看出来IntObjectHashMap更加节省内存
结论: 可以使用IntObjectHashMap替换Map<Integer,Object>,因为IntObjectHashMap的key是int类型，而Map<Integer,Object>的key是Integer类型，是对象类型
int类型占4个字节，对象类型占用字节比基本类型int大，有兴趣可以搜索 一个对象占用几个字节

参考链接

https://docs.oracle.com/javase/7/docs/technotes/tools/index.html#troubleshoot

未完待续...