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：
```java
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:
```java
String watchExpress = "{target, params, returnObj, #cost }";
String conditionExpress = "params[0] > 1 && #cost > 0.1";
```
The result is similar to the following expression:
```bash
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:
```java
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:
```java
String watchExpress = "{target, params, throwExp}";
String conditionExpress = "params[0] > 1";
```
The result is similar to the following expression:
```bash
watch com.example.ognl.TestService test "{target, params, throwExp}" "params[0] > 1" -e -x 2
```
