Critical Fields in Expressions

There is a very fundamental class Advice for the expressions used in filtering, tracing or monitoring and other aspects in commands.

public class Advice {

    private final ClassLoader loader;
    private final Class<?> clazz;
    private final ArthasMethod method;
    private final Object target;
    private final Object[] params;
    private final Object returnObj;
    private final Throwable throwExp;
    private final boolean isBefore;
    private final boolean isThrow;
    private final boolean isReturn;
    ...
    // getter/setter  
}  

Name	Specification
loader	class loader of the class
clazz	the reference of the class
method	the reflective reference of the method
target	the instance of the class
params	the parameters of the method, which is an array (when there is no argument in the method, it will be an empty array)
returnObj	the return value of the method - only when isReturn==true, it's a valid result but if the return value is void then it will be a null
throwExp	the exceptions thrown by the method invoking - only when isThrow==true, it's a valid thrown exception
isBefore	assistant checking flag used in before-watching point and at this very moment: isBefore==true, isThrow==false and isReturn==false since it's before we invoke the method
isThrow	assistant checking flag: whether the current method invoking ends with exceptions
isReturn	assistant checking flag: whether the method invoking exits normally without exceptions

F.Y.I

1. all the fields mentioned in the table above can be used directly in the expressions;
2. if the expressions are invalid OGNL, the command will be cancelled automatically with hints to correct the expressions;
3. typical use cases;
4. OGNL official usage guide.