Java 代码获取 JVM 参数

运行时诊断：代码中读取 JVM 状态

除了命令行工具，Java 代码本身也提供了丰富的 API 来获取 JVM 和运行时信息。这一节介绍如何在代码中诊断和获取 JVM 参数。

ManagementFactory：获取管理 MXBean

java.lang.management.ManagementFactory 是获取 JVM 运行时信息的入口：

java

import java.lang.management.*;

public class JvmDiagnostics {
    public static void main(String[] args) {
        // 获取内存管理 MXBean
        MemoryMXBean memoryMXBean = ManagementFactory.getMemoryMXBean();
        System.out.println("堆内存使用：" + memoryMXBean.getHeapMemoryUsage());
        System.out.println("非堆内存使用：" + memoryMXBean.getNonHeapMemoryUsage());

        // 获取类加载 MXBean
        ClassLoadingMXBean classLoadingMXBean = ManagementFactory.getClassLoadingMXBean();
        System.out.println("已加载类数量：" + classLoadingMXBean.getLoadedClassCount());
        System.out.println("总加载类数量：" + classLoadingMXBean.getTotalLoadedClassCount());

        // 获取运行时 MXBean
        RuntimeMXBean runtimeMXBean = ManagementFactory.getRuntimeMXBean();
        System.out.println("JVM 名称：" + runtimeMXBean.getVmName());
        System.out.println("JVM 版本：" + runtimeMXBean.getVmVersion());
        System.out.println("启动时间：" + new Date(runtimeMXBean.getStartTime()));
        System.out.println("运行时间：" + runtimeMXBean.getUptime() + " ms");
    }
}

内存信息：MemoryMXBean

堆内存使用

java

import java.lang.management.MemoryMXBean;
import java.lang.management.MemoryUsage;
import java.lang.management.ManagementFactory;

public class MemoryInfo {
    public static void main(String[] args) {
        MemoryMXBean memoryMXBean = ManagementFactory.getMemoryMXBean();

        // 堆内存使用
        MemoryUsage heapUsage = memoryMXBean.getHeapMemoryUsage();
        System.out.println("=== 堆内存 ===");
        System.out.println("初始大小：" + bytesToMB(heapUsage.getInit()) + " MB");
        System.out.println("已使用：" + bytesToMB(heapUsage.getUsed()) + " MB");
        System.out.println("最大限制：" + bytesToMB(heapUsage.getMax()) + " MB");
        System.out.println("已提交：" + bytesToMB(heapUsage.getCommitted()) + " MB");
        System.out.println("使用率：" + String.format("%.2f%%",
            (double) heapUsage.getUsed() / heapUsage.getMax() * 100));

        // 非堆内存（元空间）
        MemoryUsage nonHeapUsage = memoryMXBean.getNonHeapMemoryUsage();
        System.out.println("\n=== 非堆内存 ===");
        System.out.println("已使用：" + bytesToMB(nonHeapUsage.getUsed()) + " MB");
        System.out.println("最大限制：" + (nonHeapUsage.getMax() == -1 ? "无限制" :
            bytesToMB(nonHeapUsage.getMax()) + " MB"));
    }

    private static long bytesToMB(long bytes) {
        return bytes / 1024 / 1024;
    }
}

获取各内存池使用

java

import java.lang.management.*;
import java.util.*;

public class MemoryPools {
    public static void main(String[] args) {
        List<MemoryPoolMXBean> pools = ManagementFactory.getMemoryPoolMXBeans();

        for (MemoryPoolMXBean pool : pools) {
            String name = pool.getName();
            MemoryType type = pool.getType();
            MemoryUsage usage = pool.getUsage();

            System.out.println("=== " + name + " (" + type + ") ===");
            System.out.println("已使用：" + usage.getUsed() / 1024 / 1024 + " MB");
            System.out.println("最大：" + (usage.getMax() == -1 ? "无限制" :
                usage.getMax() / 1024 / 1024 + " MB"));
        }
    }
}

GC 信息：GarbageCollectorMXBean

java

import java.lang.management.*;
import java.util.*;

public class GcInfo {
    public static void main(String[] args) {
        List<GarbageCollectorMXBean> gcBeans = ManagementFactory.getGarbageCollectorMXBeans();

        System.out.println("=== GC 信息 ===");
        for (GarbageCollectorMXBean gc : gcBeans) {
            System.out.println("GC 名称：" + gc.getName());
            System.out.println("收集次数：" + gc.getCollectionCount());
            System.out.println("总耗时：" + gc.getCollectionTime() + " ms");

            // 内存池名称
            String[] poolNames = gc.getMemoryPoolNames();
            System.out.println("管理的内存池：" + Arrays.toString(poolNames));
        }
    }
}

线程信息：ThreadMXBean

java

import java.lang.management.*;
import java.util.*;

public class ThreadInfo {
    public static void main(String[] args) {
        ThreadMXBean threadMXBean = ManagementFactory.getThreadMXBean();

        System.out.println("=== 线程信息 ===");
        System.out.println("活动线程数：" + threadMXBean.getThreadCount());
        System.out.println("峰值线程数：" + threadMXBean.getPeakThreadCount());
        System.out.println("总启动线程数：" + threadMXBean.getTotalStartedThreadCount());
        System.out.println("守护线程数：" + threadMXBean.getDaemonThreadCount());

        // 获取所有线程信息
        long[] threadIds = threadMXBean.getAllThreadIds();
        System.out.println("\n=== 所有线程 ===");
        for (long tid : threadIds) {
            ThreadInfo info = threadMXBean.getThreadInfo(tid);
            if (info != null) {
                System.out.println("线程: " + info.getThreadName() +
                    " | 状态: " + info.getThreadState() +
                    " | CPU: " + threadMXBean.getThreadCpuTime(tid) / 1_000_000 + " ms");
            }
        }
    }
}

运行时信息：RuntimeMXBean

java

import java.lang.management.*;
import java.util.*;

public class RuntimeInfo {
    public static void main(String[] args) {
        RuntimeMXBean runtimeMXBean = ManagementFactory.getRuntimeMXBean();

        System.out.println("=== JVM 信息 ===");
        System.out.println("JVM 名称：" + runtimeMXBean.getVmName());
        System.out.println("JVM 供应商：" + runtimeMXBean.getVmVendor());
        System.out.println("JVM 版本：" + runtimeMXBean.getVmVersion());
        System.out.println("Java 版本：" + System.getProperty("java.version"));
        System.out.println("Java 主页：" + System.getProperty("java.home"));

        System.out.println("\n=== 启动信息 ===");
        System.out.println("启动时间：" + new Date(runtimeMXBean.getStartTime()));
        System.out.println("运行时间：" + runtimeMXBean.getUptime() / 1000 + " 秒");

        System.out.println("\n=== 系统属性 ===");
        Map<String, String> props = runtimeMXBean.getSystemProperties();
        props.forEach((k, v) -> System.out.println(k + "=" + v));
    }
}

编译信息：CompilationMXBean

java

import java.lang.management.*;

public class CompilerInfo {
    public static void main(String[] args) {
        CompilationMXBean compilerMXBean = ManagementFactory.getCompilationMXBean();

        if (compilerMXBean != null) {
            System.out.println("=== 编译信息 ===");
            System.out.println("编译器名称：" + compilerMXBean.getName());
            System.out.println("编译耗时：" + compilerMXBean.getTotalCompilationTime() + " ms");

            // 获取 JIT 编译器名称
            String compilerName = compilerMXBean.getName();
            System.out.println("JIT 编译器：" + compilerName);
        } else {
            System.out.println("JIT 编译器信息不可用");
        }
    }
}

类加载信息：ClassLoadingMXBean

java

import java.lang.management.*;

public class ClassLoadingInfo {
    public static void main(String[] args) {
        ClassLoadingMXBean classLoadingMXBean = ManagementFactory.getClassLoadingMXBean();

        System.out.println("=== 类加载信息 ===");
        System.out.println("当前加载类数：" + classLoadingMXBean.getLoadedClassCount());
        System.out.println("总加载类数：" + classLoadingMXBean.getTotalLoadedClassCount());
        System.out.println("已卸载类数：" + classLoadingMXBean.getUnloadedClassCount());
        System.out.println("类加载是否启用：" + classLoadingMXBean.isVerbose());
    }
}

操作系统信息：OperatingSystemMXBean

java

import java.lang.management.*;
import java.lang.reflect.*;

public class OsInfo {
    public static void main(String[] args) throws Exception {
        OperatingSystemMXBean osMXBean = ManagementFactory.getOperatingSystemMXBean();

        System.out.println("=== 操作系统信息 ===");
        System.out.println("系统名称：" + osMXBean.getName());
        System.out.println("系统架构：" + osMXBean.getArch());
        System.out.println("CPU 数量：" + osMXBean.getAvailableProcessors());

        // 获取系统负载（需要使用底层方法）
        System.out.println("系统负载：" + osMXBean.getSystemLoadAverage());

        // 通过反射获取更详细的信息
        for (Method method : osMXBean.getClass().getDeclaredMethods()) {
            method.setAccessible(true);
            if (method.getName().startsWith("get") &&
                method.getParameterCount() == 0) {
                Object value = method.invoke(osMXBean);
                if (value instanceof Number) {
                    System.out.println(method.getName().replace("get", "") + ": " + value);
                }
            }
        }
    }
}

监控接口：MonitoringMXBean

通过 JMX 暴露监控数据

java

import java.lang.management.*;
import javax.management.*;

public class JmxExporter {
    public static void main(String[] args) throws Exception {
        // 获取 MBean Server
        MBeanServer mbs = ManagementFactory.getPlatformMBeanServer();

        // 注册一个自定义 MBean
        ObjectName name = new ObjectName("com.example:type=AppMonitor");
        AppMonitorMBean mbean = new AppMonitor();
        mbs.registerMBean(mbean, name);

        System.out.println("AppMonitor MBean 已注册，JMX 端口："
            + ManagementFactory.getPlatformMBeanServer());

        // 等待
        Thread.sleep(Long.MAX_VALUE);
    }
}

public interface AppMonitorMBean {
    long getRequestCount();
    void incrementRequestCount();
}

public class AppMonitor implements AppMonitorMBean {
    private long requestCount = 0;

    @Override
    public long getRequestCount() {
        return requestCount;
    }

    @Override
    public void incrementRequestCount() {
        requestCount++;
    }
}

完整示例：健康检查端点

java

import org.springframework.web.bind.annotation.*;
import java.lang.management.*;
import java.util.*;

@RestController
@RequestMapping("/api/health")
public class HealthController {

    @GetMapping("/jvm")
    public Map&lt;String, Object&gt; getJvmHealth() {
        Map&lt;String, Object&gt; health = new HashMap&lt;&gt;();

        // 内存
        MemoryMXBean memory = ManagementFactory.getMemoryMXBean();
        MemoryUsage heap = memory.getHeapMemoryUsage();
        health.put("heapUsed", heap.getUsed());
        health.put("heapMax", heap.getMax());
        health.put("heapUsedPercent",
            String.format("%.2f%%", (double) heap.getUsed() / heap.getMax() * 100));

        // GC
        List&lt;GarbageCollectorMXBean&gt; gcBeans = ManagementFactory.getGarbageCollectorMXBeans();
        long totalGcCount = 0;
        long totalGcTime = 0;
        for (GarbageCollectorMXBean gc : gcBeans) {
            totalGcCount += gc.getCollectionCount();
            totalGcTime += gc.getCollectionTime();
        }
        health.put("gcCount", totalGcCount);
        health.put("gcTimeMs", totalGcTime);

        // 线程
        ThreadMXBean threads = ManagementFactory.getThreadMXBean();
        health.put("threadCount", threads.getThreadCount());
        health.put("peakThreadCount", threads.getPeakThreadCount());
        health.put("daemonThreadCount", threads.getDaemonThreadCount());

        // 类加载
        ClassLoadingMXBean classes = ManagementFactory.getClassLoadingMXBean();
        health.put("loadedClassCount", classes.getLoadedClassCount());

        // 运行时
        RuntimeMXBean runtime = ManagementFactory.getRuntimeMXBean();
        health.put("uptimeMs", runtime.getUptime());
        health.put("vmName", runtime.getVmName());
        health.put("vmVersion", runtime.getVmVersion());

        return health;
    }
}

常用 API 速查

API	作用	关键方法
`ManagementFactory.getMemoryMXBean()`	内存信息	`getHeapMemoryUsage()`
`ManagementFactory.getGarbageCollectorMXBeans()`	GC 信息	`getCollectionCount()`
`ManagementFactory.getThreadMXBean()`	线程信息	`getThreadCount()`
`ManagementFactory.getRuntimeMXBean()`	JVM 信息	`getVmName()`
`ManagementFactory.getClassLoadingMXBean()`	类加载信息	`getLoadedClassCount()`
`ManagementFactory.getOperatingSystemMXBean()`	OS 信息	`getAvailableProcessors()`
`ManagementFactory.getCompilationMXBean()`	编译信息	`getTotalCompilationTime()`
`ManagementFactory.getPlatformMBeanServer()`	MBean Server	JMX 暴露

本节小结

Java 代码获取 JVM 参数的核心 API 是 ManagementFactory，它提供了访问所有 MXBean 的入口：

ManagementFactory 核心 MXBean：
MemoryMXBean         → 堆/非堆内存使用
GarbageCollectorMXBean → GC 次数和耗时
ThreadMXBean          → 线程数量和状态
RuntimeMXBean         → JVM 版本、启动时间
ClassLoadingMXBean   → 类加载数量
OperatingSystemMXBean → OS 信息
CompilationMXBean     → JIT 编译信息

实际应用：在 Spring Boot Actuator、Dropsonde 等框架中，这些 API 被广泛用于暴露 /actuator/metrics 端点。

下一节，我们来看 OOM 及性能优化案例与解决方案。

虚拟机栈（核心）

堆空间（核心）

方法区（永久代/元空间）

G1 回收器（核心）

命令行工具

GUI 工具

Arthas（核心）

Java 代码获取 JVM 参数

运行时诊断：代码中读取 JVM 状态

ManagementFactory：获取管理 MXBean

内存信息：MemoryMXBean

堆内存使用

获取各内存池使用

GC 信息：GarbageCollectorMXBean

线程信息：ThreadMXBean

运行时信息：RuntimeMXBean

编译信息：CompilationMXBean

类加载信息：ClassLoadingMXBean

操作系统信息：OperatingSystemMXBean

监控接口：MonitoringMXBean

通过 JMX 暴露监控数据

完整示例：健康检查端点

常用 API 速查

本节小结

Java 代码获取 JVM 参数 ​

运行时诊断：代码中读取 JVM 状态 ​

ManagementFactory：获取管理 MXBean ​

内存信息：MemoryMXBean ​

堆内存使用 ​

获取各内存池使用 ​

GC 信息：GarbageCollectorMXBean ​

线程信息：ThreadMXBean ​

运行时信息：RuntimeMXBean ​

编译信息：CompilationMXBean ​

类加载信息：ClassLoadingMXBean ​

操作系统信息：OperatingSystemMXBean ​

监控接口：MonitoringMXBean ​

通过 JMX 暴露监控数据 ​

完整示例：健康检查端点 ​

常用 API 速查 ​

本节小结 ​

Java 代码获取 JVM 参数

运行时诊断：代码中读取 JVM 状态

ManagementFactory：获取管理 MXBean

内存信息：MemoryMXBean

堆内存使用

获取各内存池使用

GC 信息：GarbageCollectorMXBean

线程信息：ThreadMXBean

运行时信息：RuntimeMXBean

编译信息：CompilationMXBean

类加载信息：ClassLoadingMXBean

操作系统信息：OperatingSystemMXBean

监控接口：MonitoringMXBean

通过 JMX 暴露监控数据

完整示例：健康检查端点

常用 API 速查

本节小结