Advanced Java Learning How to Turn on Remote Adjustments

Overview

Opening and underlying principles of Java remote debugging

Turn on Java remote debugging

Java Remote Debugging allows developers to debug Java applications running on remote servers in local IDEs (such as Eclipse, IntelliJ IDEA, etc.). The following are the basic steps to enable Java remote debugging:

• Configure Java applications on remote servers：

  • When starting a Java application, enable remote debugging by adding JVM parameters. These parameters usually include、(Specify the debug port),(usually set toyorn, depending on whether it is server mode), etc., but in actual use, what we use more often is-agentlib:jdwpParameters and their subparameters.
  • For example, suppose we want to enable remote debugging on port 5005, we can add the following parameters to the startup command:

    java -agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=5005 -jar 
    

    • transport=dt_socket: Specify the use of socket transfer.
    • server=y: Indicates that the current JVM is used as a debugging server.
    • suspend=n: means that the JVM does not pause when started and executes immediately. If set toy, the JVM will pause while waiting for the debugger to connect.
    • address=5005: Specify the debug port.

• Configure local IDE：

  • Create a remote debug configuration in the IDE.
  • Specifies the IP address and debug port of the remote host (same as configured on the server).
  • Connect and start debugging.

The underlying principle

The underlying principle of Java remote debugging mainly relies on the debugging interfaces of Java Debug Wire Protocol (JDWP) and Java virtual machine (JVM).

• JDWP：

  • JDWP is a communication protocol for Java application debugging. It defines the communication specification between the debugger (debug tool in the IDE) and the debugged Java virtual machine (JVM).
  • JDWP supports a variety of debugging functions, such as setting breakpoints, stepping, viewing variable values, monitoring threads, etc.
  • JDWP uses sockets (Sockets) as the communication transport layer, so network connections need to be established between the debugger and the JVM.

• JVM debugging interface：

  • The JVM provides a debugging interface (commonly called Java Virtual Machine Tool Interface, JVMTI or Java Debug Interface, JDI) that allows the debugger to interact with the JVM.
  • When the JVM starts, if-agentlib:jdwpParameters, the JVM will load the JDWP proxy library. This proxy library implements the JDWP protocol and serves as a bridge between the JVM and the debugger.
  • The debugger sends debug commands to the JVM through the JDWP protocol, and the JVM receives these commands through the JDWP proxy library and performs corresponding debugging operations according to the commands.

• Communication process：

  • When the debugger connects to a remote JVM, a JDWP session is established between them.
  • The debugger can send various JDWP commands to query the status of the JVM, control the execution of the JVM (such as pausing and restoring threads), read and modify variable values, etc.
  • The JVM receives these commands through the JDWP proxy library and calls the corresponding JVM debugging interface to implement the debugging function.
  • Data during debugging (such as variable values, thread states, etc.) will also be transferred between the debugger and the JVM through the JDWP protocol.

In short, Java remote debugging realizes communication and interaction between the debugger and the remote JVM through the JDWP protocol and the JVM debugging interface. Developers can easily debug Java applications running on remote servers in the local IDE.

JVM parameters

The following are some common JVM parameters, displayed in table form, and are attached with examples of use:

Parameter Category	Parameter name	illustrate	Examples of use
Standard parameters	-version	Display Java version information	java -version
	-help	Show Java commands help	java -help
	-server	Start the JVM in Server mode	java -server -jar
	-cp or -classpath	Specify the class search path	java -cp .;lib/ MyApp
Non-standard parameters (-X)	-Xint	Explain execution, not perform JIT compilation	java -Xint -jar
	-Xcomp	Compile local code for the first time	java -Xcomp -jar
	-Xmixed	Mixed mode, the JVM decides whether to explain or compile the execution	java -Xmixed -jar
Non-standardized parameters (-XX)	Boolean Type	-XX:[±]name	java -XX:+UseG1GC -jar (enable G1 garbage collector)
			java -XX:-UseConcMarkSweepGC -jar (disable CMS garbage collector)
	Non-Boolean type	-XX:name=value	java -XX:MaxGCPauseMillis=500 -jar (set the maximum GC pause time to 500 milliseconds)
			java -XX:HeapDumpPath=/path/to/dump -jar (set the heap dump file path)
Memory management	-Xms	Set the initial heap memory size of JVM	java -Xms512m -jar （512MB）
	-Xmx	Set the maximum heap memory size of JVM	java -Xmx2g -jar （2GB）
	-Xmn	Set the new generation size	java -Xmn256m -jar （256MB）
	-XX:NewRatio	Set the ratio of the new generation to the old generation	java -XX:NewRatio=3 -jar (New Generation: Old Generation=1:3)
	-XX:SurvivorRatio	Set the ratio of Eden area to Survivor area	java -XX:SurvivorRatio=4 -jar （Eden:Survivor=4:1）
Garbage recycling	-XX:+UseG1GC	Enable G1 garbage collector	As shown above
	-XX:+UseConcMarkSweepGC	Enable CMS garbage collector (before Java 9)	As shown in the disable example above
	-XX:+HeapDumpOnOutOfMemoryError	Generate heap dump file when memory overflows	As shown in the example setting heap dump path above, you can use it in combination with this parameter
Performance optimization	-XX:+TieredCompilation	Enable multi-level compiler	java -XX:+TieredCompilation -jar
	-XX:+UseCompressedOops	Enable pointer compression	java -XX:+UseCompressedOops -jar
Debugging and monitoring	-XX:+PrintGCDetails	Print detailed GC logs	java -XX:+PrintGCDetails -jar
	-XX:+PrintGCDateStamps	Print the time stamp that occurs when GC	java -XX:+PrintGCDateStamps -jar
	-Xloggc:	Specify the path to the GC log file	java -Xloggc: -jar

Notice：

• The parameters in the above table are examples only and not all JVM parameters. There are many JVM parameters, and as Java versions are updated, new parameters may be introduced or old parameters may be discarded.
• In actual use, parameters should be configured and tuned according to the specific needs of the application and the hardware environment.
• Some parameters may need to be valid in a specific JVM version or mode.
• When using non-standard parameters (-X and -XX), be cautious, as these parameters may vary in different versions of the JVM and some parameters may cause unstable JVM behavior or performance degradation.

Summarize

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