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45 lines
2.0 KiB
Plaintext
45 lines
2.0 KiB
Plaintext
Fundamental Fields in Expressions
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There is a very fundamental class `Advice` for the expressions used in filtering, tracing or monitoring and other aspects in commands.
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```java
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public class Advice {
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private final ClassLoader loader;
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private final Class<?> clazz;
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private final ArthasMethod method;
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private final Object target;
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private final Object[] params;
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private final Object returnObj;
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private final Throwable throwExp;
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private final boolean isBefore;
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private final boolean isThrow;
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private final boolean isReturn;
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// getter/setter
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}
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```
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Description for the variables in the class `Advice`:
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|Name|Specification|
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|---:|:---|
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|loader|the class loader for the current called class|
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|clazz|the reference to the current called class|
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|method|the reference to the current called method|
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|target|the instance of the current called class|
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|params|the parameters for the current call, which is an array (when there's no parameter, it will be an empty array)|
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|returnObj|the return value from the current call - only available when the method call returns normally (`isReturn==true`), and `null` is for `void` return value|
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|throwExp|the exceptions thrown from the current call - only available when the method call throws exception (`isThrow==true`)|
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|isBefore|flag to indicate the method is about to execute. `isBefore==true` but `isThrow==false` and `isReturn==false` since it's no way to know how the method call will end|
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|isThrow|flag to indicate the method call ends with exception thrown|
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|isReturn|flag to indicate the method call ends normally without exception thrown|
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All variables listed above can be used directly in the [OGNL expression](https://commons.apache.org/proper/commons-ognl/language-guide.html). The command will not execute and exit if there's illegal OGNL grammar or unexpected variable in the expression.
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* [typical use cases](https://github.com/alibaba/arthas/issues/71);
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* [OGNL language guide](https://commons.apache.org/proper/commons-ognl/language-guide.html).
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