arthas/tutorials/katacoda/case-ognl-practise-en/step1.md

Demonstrate the workflow of the ognl expression in the watch command in Arthas. You can modify the expressions in Demo.java, and compile and run the code.

Project: https://github.com/hengyunabc/ognl-demo

Open the Demo.java file

src/main/java/com/example/ognl/Demo.java{{open}}

Compile and run the code

mvn compile exec:java{{execute}}

输出结果包含ognl表达式输出结果：

AtEnter, conditionExpress: params[0] > 1, conditionResult: true
@ArrayList[
    @TestService[
    ],
    @Object[][
        @Integer[1000],
        @String[hello],
        @Student[
            id=@Long[1],
            name=@String[tom],
        ],
    ],
]

Expression in the code:

String watchExpress = "{target, params, returnObj, #cost}";
String conditionExpress = "params[0] > 1 && #cost > 0.1";

The result is similar to the following expression:

watch com.example.ognl.TestService test "{target, params, returnObj, #cost}" "params[0] > 1 && #cost > 0.1" -x 3

View the expression result when the method throws an exception

mvn compile exec:java -DexceptionCase=true{{execute}}

The output:

AtExceptionExit, conditionExpress: params[0] > 1, conditionResult: true
@ArrayList[
    @TestService[
    ],
    @Object[][
        @Integer[1000],
        @String[hello],
        @Student[com.example.ognl.Student@6e23bcdd],
    ],
    java.lang.IllegalArgumentException: error
        at com.example.ognl.TestService.test(TestService.java:12)
        at com.example.ognl.Demo.test(Demo.java:43)
        at com.example.ognl.Demo.main(Demo.java:20)
        at org.codehaus.mojo.exec.ExecJavaMojo$1.run(ExecJavaMojo.java:254)
        at java.base/java.lang.Thread.run(Thread.java:832)
,
]

Expression in the code:

String watchExpress = "{target, params, throwExp}";
String conditionExpress = "params[0] > 1";

The result is similar to the following expression:

watch com.example.ognl.TestService test "{target, params, throwExp}" "params[0] > 1" -e -x 2