How to check jvm memory usage

Methods to check jvm memory usage: 1. Use command line tools; 2. Use JMX; 3. Use Java code; 4. Use VisualVM; 5. Use MAT; 6. Use Java Mission Control; 7 , custom monitoring and analysis tools. Detailed introduction: 1. Use the command line tool, you can use the jstat command line tool to view the memory usage of the JVM; 2. Use JMX, which is a standard API of the Java platform, used to manage and monitor Java applications, etc.

The operating system for this tutorial: Windows 10 system, DELL G3 computer.

Viewing JVM memory usage can help you understand the memory usage of the application, so as to perform performance tuning and troubleshooting. The following are some common methods to check JVM memory usage:

1. Use command line tools

You can use the jstat command line tool to check JVM memory usage Condition.

* `jstat -gcutil <pid>%<interval>`：此命令用于监视堆内存使用情况，其中`<pid>`是JVM进程的ID，`<interval>`是采样间隔（以秒为单位）。  
* `jstat -gccapacity <pid>%<interval>`：此命令用于监视JVM的各个内存区域的大小。  
* `jstat -printcompilation <pid>%<interval>`：此命令用于显示已编译方法的统计信息。

2. Use JMX (Java Management Extensions)

JMX is a standard API of the Java platform for managing and monitoring Java applications. You can use tools like JConsole or VisualVM to connect to the JVM process and view its memory usage.

3. Using Java code

You can use Java's Runtime class or ManagementFactory class to obtain the memory usage of the JVM.

* 使用`Runtime`类：  
```  
java`long totalMemory = Runtime.getRuntime().totalMemory();  
long freeMemory = Runtime.getRuntime().freeMemory();  
long usedMemory = totalMemory - freeMemory;`  
```  
* 使用`ManagementFactory`类：   
```  
java`MemoryMXBean memoryMXBean = ManagementFactory.getMemoryMXBean();  
MemoryUsage heapUsage = memoryMXBean.getHeapMemoryUsage();  
long usedHeapMemory = heapUsage.getUsed();`  
```这些代码片段可以帮助你获取JVM的内存使用情况。请注意，这些方法提供的信息可能不如其他工具详细。

4. Using VisualVM

VisualVM is a powerful tool that can be used to view, monitor and debug Java applications. It provides a comprehensive view of the JVM, including memory usage, threads, CPU and memory profiling, heap dump analysis, and more. You can connect to a running application through VisualVM, view its memory usage and gather other useful information.

5. Use MAT (Memory Analyzer Tool)

MAT is a tool for analyzing Java heap dumps. It can be used to analyze heap dump files to help you find memory leaks and other memory problems. MAT provides rich functions, such as object size analysis, memory leak detection, thread analysis, etc. You can use MAT to open a heap dump file and view its contents to gain insight into your application's memory usage.

6. Use Java Mission Control

Java Mission Control is a monitoring and analysis tool provided by Oracle, which can be used to view JVM performance indicators and configuration information. It provides rich functions, such as memory profiling, garbage collection analysis, thread analysis, etc. You can use Java Mission Control to connect to a JVM process and view its memory usage and other performance metrics.

7. Customized monitoring and analysis tools

If you need more customized monitoring and analysis tools, you can consider developing your own tools or integrating third-party tools . There are many open source tools and frameworks available for monitoring and analyzing Java application performance metrics, including memory usage. You can choose the right tool based on your needs and customize development as needed.

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