Arthas watch command to view the properties of objects in the array

Look at the elements in the array

Love it Arthas , Helped me troubleshoot many code problems .
In use today Arthas Of watch When the command checks the input parameters of a method , It is found that the corresponding input parameter object is a little complex , Roughly, an object contains an array object , Then I need an attribute in the corresponding array object . Because I haven't encountered such a scene before , So I'm writing watch I don't know how to write the order , After looking for a long time, I finally found the corresponding writing method , Sit down here and sum up .

public class Main{
    
	public static void method1(OrgDTO org){
    
		// do nothing
	}
}
public class OrgDTO{
    
	private String name;
	private List<OrgDTO> children;
}

The above is probably the scene I encountered , I need to get method1 Method into the children Of each element in name attribute , After checking the information , Knowing this kind of scene is called Attribute projection / Set projection / Expression projection .

Use ognl The expression is written as {params[0].children.{name}}:

watch org.example.Main method1 {
    params[0].children.{
    name}} -x 2

Call the method of each element in the array
Of course , The above is a simple way of writing , In fact, we can also call the methods of each object , Get its return result :{params[0].children.{getName()}}.

watch org.example.Main method1 {
    params[0].children.{
    getName()}} -x 2

In this way , We can get children For each object in the array getName() Return value of method .
Use expressions to filter
There is another way to filter expressions , You can specify filter conditions in curly braces to filter array objects :

#  Filter  children  Name length is greater than 5 The elements of 
watch org.example.Main method1 {
    params[0].children.{
    ? name.length() > 5}} -x 2

First summarize these , In fact, the corresponding parameter viewing method is very flexible , The following resources have been introduced in great detail , You can take what you need .

Reference material

Arthas file
Flexible use ognl expression
ognl Official documents
Arthas Some special usage documentation for