性能指标与测量
Java 代码优化
Pavlos Kosmetatos
Lead Engineer @Wealthyhood
超越时间测量
- 前面的视频
- 测量操作耗时
- JVM 内存管理
- 超越时间测量
- 内存指标
- CPU 利用率指标
使用 Runtime 获取内存指标
// Get the Runtime instance Runtime runtime = Runtime.getRuntime();// Memory metrics in bytes long totalMemory = runtime.totalMemory(); // Memory currently allocated long freeMemory = runtime.freeMemory(); // Memory that is unused long maxMemory = runtime.maxMemory(); // Maximum memory JVM will attempt to use
- 都返回以字节为单位的
long数值
理解内存指标
maxMemory()：JVM 试图使用的最大内存（由 -Xmx 设置）totalMemory()：JVM 当前已分配的内存freeMemory()：未使用的内存usedMemory()：totalMemory - freeMemory- JVM 可按需将
totalMemory增长至maxMemory
内存指标实战
// Create a utility method for readable memory values
public static double getUsedMemoryMB() {
Runtime runtime = Runtime.getRuntime();
long memory = runtime.totalMemory() - runtime.freeMemory();
return memory / (1024.0 * 1024.0); // Convert to MB
}
// After allocation
System.out.println("Memory used: " + getUsedMemoryMB() + " MB");
Memory used: 5.23 MB
CPU 利用率测量
import java.lang.management.*; ThreadMXBean threadMXBean = ManagementFactory.getThreadMXBean();// Check if CPU time measurement is supported if (threadMXBean.isThreadCpuTimeSupported()) { // Enable CPU time measurement threadMXBean.setThreadCpuTimeEnabled(true); // Get CPU time in nanoseconds long cpuTimeNs = threadMXBean.getThreadCpuTime(Thread.currentThread().threadId()); }
Java 分析工具
- JVisualVM：用于监控内存、CPU 等的可视化界面
- jmap：命令行内存分析工具
- 这些工具超越了我们已讨论的简单指标！
Passons à la pratique !
Java 代码优化
