Ali Open Source Java Diagnostic Tool-Arthas

Arthas is an open source tool for Java developed by Alibaba recently. It mainly for diagnosing the problems of java.

I. Overview

This tool can help you do the following things:

  1. Which jar package loaded this class from?
  2. Why do you code throws various kinds of Exceptions?
  3. If you encounter problems on product environment , you can’t debug well. Can you only add System.out on your code and republish it again and again to find problem by adding logs?
  4. Why hasn’t the online code been executed here? Is it because there is no commit in the code? Or is it the wrong branch code?
  5. There is a problem with the data processing of a user online, but it can not debug online and can not be reappear offline.
  6. Is there a global perspective to see how the system works?
  7. What is the way to monitor the real-time running state of JVM?

II. Installation Method

1.1 Windows Installation Mode

Download address:

After downloading, decompress, as shown in the following:

Download the latest “” package file. After decompression, there is a file named “as.bat” in the bin directory. For the time being, this script accepts only one parameter “pid”, so it can only diagnose Java processes on one machine.

The startup command is:

as.bat <pid>

Note: When I started Windows 10, I encountered the following problems

D:\download\arthas-packaging-3.0.4-bin > telnet 'telnet'is not an internal or external command, nor is it a runnable program Or batch files.

The solution is: Control Panel – > Start or Close Windows Function – > Check Telnet Function

1.2 Linux Installation Mode

Install Arthas:

curl -L | sh

Start Arthas:


After successful startup, you will see the following interface.

III. Common orders

3.1 Basic Command

Help — View command help information
CLS – Clear the current screen area
Session — View information about the current session
Reset – Reset Enhanced Classes, which will be restored to all classes enhanced by Arthas. When the Arthas server is closed, all enhanced classes will be reset.
Version — Outputs the version number of Arthas loaded by the current target Java process
Quit – Exit the current Arthas client, other Arthas clients are unaffected
Shutdown – Close the Arthas server and all Arthas clients quit
Keymap – Arthas shortcut list and custom shortcut keys

JVM correlation

Dashboard – Real-time Data Panel for Current System
Thread — View thread stack information for the current JVM
JVM — View the current JVM information
Sysprop — Viewing and modifying JVM system properties
New! Getstatic — View static properties of classes

Class / classloader correlation

SC — View class information loaded by JVM
SM — View method information for loaded classes
Dump – dump loaded class byte code to a specific directory
Redefine – Load external. class files, redefine to JVM
JAD — Decompiles the source code that specifies the loaded class
Classloader – View the inheritance tree, urls, class loading information of classloader, and use classloader to getResource

Monitor/watch/trace correlation

Note that these commands are implemented by bytecode enhancement technology, which inserts some aspect into the method of the specified class to achieve data statistics and observation. Therefore, when online and pre-sent, please try to identify the classes, methods and conditions that need to be observed, and execute shutdown command at the end of diagnosis or execute reset command for enhanced class.

Monitor — Method Execution Monitoring
Watch – Method Executes Data Observation
Trace — Invoke paths within methods and output time-consuming paths on each node on the method path
Stack — Outputs the call path for the current method to be invoked
TT – Method executes the time-space tunnel of data, records the input and return information of each call of the specified method, and can observe these calls at different times.


Options — View or set the Arthas global switch


Arthas supports the use of pipes to further process the results of the above commands, such as SM org. apache. log4j. Logger | grep
Grep — Search for results that satisfy conditions
Plaintext — Remove the color from the result of the command
WC – Statistical output by line

Web Console

Connect Arthas through websocket.

Other features

Asynchronous command support
Execution results are logged
Batch processing support
Usage Description of ognl Expressions

3.2 Use examples

First, in the window, enter help to see all available commands provided (the communication is essentially through telnet protocol), as follows:

Attach success.
Connecting to arthas server... current timestamp is 1537266148
Connected to
Escape character is '^]'.
  ,---.  ,------. ,--------.,--.  ,--.  ,---.   ,---.                           
 /  O  \ |  .--. ''--.  .--'|  '--'  | /  O  \ '   .-'                          
|  .-.  ||  '--'.'   |  |   |  .--.  ||  .-.  |`.  `-.                          
|  | |  ||  |\  \    |  |   |  |  |  ||  | |  |.-'    |                         
`--' `--'`--' '--'   `--'   `--'  `--'`--' `--'`-----'                          

version: 3.0.4
pid: 25206
timestamp: 1537266148841

$ help
 NAME         DESCRIPTION                                                                                                                                                                      
 help         Display Arthas Help                                                                                                                                                              
 keymap       Display all the available keymap for the specified connection.                                                                                                                   
 sc           Search all the classes loaded by JVM                                                                                                                                             
 sm           Search the method of classes loaded by JVM                                                                                                                                       
 classloader  Show classloader info                                                                                                                                                            
 jad          Decompile class                                                                                                                                                                  
 getstatic    Show the static field of a class                                                                                                                                                 
 monitor      Monitor method execution statistics, e.g. total/success/failure count, average rt, fail rate, etc.                                                                               
 stack        Display the stack trace for the specified class and method                                                                                                                       
 thread       Display thread info, thread stack                                                                                                                                                
 trace        Trace the execution time of specified method invocation.                                                                                                                         
 watch        Display the input/output parameter, return object, and thrown exception of specified method invocation                                                                           
 tt           Time Tunnel                                                                                                                                                                      
 jvm          Display the target JVM information                                                                                                                                               
 dashboard    Overview of target jvm's thread, memory, gc, vm, tomcat info.                                                                                                                    
 dump         Dump class byte array from JVM                                                                                                                                                   
 options      View and change various Arthas options                                                                                                                                           
 cls          Clear the screen                                                                                                                                                                 
 reset        Reset all the enhanced classes                                                                                                                                                   
 version      Display Arthas version                                                                                                                                                           
 shutdown     Shut down Arthas server and exit the console                                                                                                                                     
 session      Display current session information                                                                                                                                              
 sysprop      Display, and change the system properties.                                                                                                                                       
 redefine     Redefine classes. @see Instrumentation#redefineClasses(ClassDefinition...)                                                                                                       

Here we mainly talk about watch, which monitors variables.

First, paste my test code:

package com.oct.tail;

import java.util.UUID;

 * @Author Ryan
 * @Date 2018/9/18  9:58
 * @desc
public class OtherTestCase {

     * @return
    public static String uuid(){
       return UUID.randomUUID().toString().replaceAll("-", "");

    public static void main(String[] args) {

            System.out.println("uuid = " + uuid());

            try {
            } catch (InterruptedException e) {

Here’s an example (I’m based on Windows 10, JDK 8 environment, Linux is the same). (For the watch command, I pretend I don’t know how to use it, and immediately enter watch help to see what’s going to happen.)

 ,---.  ,------. ,--------.,--.  ,--.  ,---.   ,---.
 /  O  \ |  .--. ''--.  .--'|  '--'  | /  O  \ '   .-'
|  .-.  ||  '--'.'   |  |   |  .--.  ||  .-.  |`.  `-.
|  | |  ||  |\  \    |  |   |  |  |  ||  | |  |.-'    |
`--' `--'`--' '--'   `--'   `--'  `--'`--' `--'`-----'

version: 3.0.4
pid: 11924
timestamp: 1537326702039

$ watch -help
   watch [-b] [-e] [-x <value>] [-f] [-h] [-n <value>] [-E] [-M <value>] [-s] class-
 pattern method-pattern express [condition-express]

   Display the input/output parameter, return object, and thrown exception of specif
 ied method invocation
   The express may be one of the following expression (evaluated dynamically):
           target : the object
            clazz : the object's class
           method : the constructor or method
     params[0..n] : the parameters of method
        returnObj : the returned object of method
         throwExp : the throw exception of method
         isReturn : the method ended by return
          isThrow : the method ended by throwing exception
            #cost : the execution time in ms of method invocation
   watch -Eb org\.apache\.commons\.lang\.StringUtils isBlank params[0]
   watch -b org.apache.commons.lang.StringUtils isBlank params[0]
   watch -f org.apache.commons.lang.StringUtils isBlank returnObj
   watch -bf *StringUtils isBlank params[0]
   watch *StringUtils isBlank params[0]
   watch *StringUtils isBlank params[0] params[0].length==1
   watch *StringUtils isBlank '#cost>100'


 -b, --before                Watch before invocation
 -e, --exception             Watch after throw exception
 -x, --expand <value>        Expand level of object (1 by default)
 -f, --finish                Watch after invocation, enable by default
 -h, --help                  this help
 -n, --limits <value>        Threshold of execution times
 -E, --regex                 Enable regular expression to match (wildcard matching b
                             y default)
 -M, --sizeLimit <value>     Upper size limit in bytes for the result (10 * 1024 * 1
                             024 by default)
 -s, --success               Watch after successful invocation
 <class-pattern>             The full qualified class name you want to watch
 <method-pattern>            The method name you want to watch
 <express>                   the content you want to watch, written by ognl.

 <condition-express>         Conditional expression in ognl style, for example:
                               TRUE  : 1==1
                               TRUE  : true
                               FALSE : false
                               TRUE  : 'params.length>=0'
                               FALSE : 1==2


Here, we monitor the return value of method UUID (). The monitoring results are as follows:

$ watch -f com.oct.tail.OtherTestCase uuid returnObj
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 18 ms.
ts=2018-09-19 11:13:48;[email protected][26c80eb505664dbcb14f8d810fb4811c]
ts=2018-09-19 11:13:49;[email protected][fc03c43864f94372b646ce6253d90646]
ts=2018-09-19 11:13:50;[email protected][55ff41e0d66347c2bc75ab8ff4ffda4e]
ts=2018-09-19 11:13:51;[email protected][c504388c0aa74458a41a1b3a77c3d536]
ts=2018-09-19 11:13:52;[email protected][18d59c09ffde4c7aab15feb88b3e433f]
ts=2018-09-19 11:13:53;[email protected][c19dd8c1e5f8442696c8f886e81e74d5]
ts=2018-09-19 11:13:54;[email protected][d37a74aa502f4897aa1ed84dc69b83d8]
ts=2018-09-19 11:13:55;[email protected][cc11753b6f424c1e9a6a1ab36f334349]
ts=2018-09-19 11:13:56;[email protected][75a9b3c0bed4426d9363168912f16d74]
ts=2018-09-19 11:13:57;[email protected][f13022118e5a4115800a6eacc480e6a8]

It works so well that I can hardly believe it.

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