How do i find out the Structure of a Java Object?

Question

I am working with the HttpExchange class, and want to use the getAttribute function to get the POST parameters. If i just call the function and print the results it works. But there has to be some better way to access the returned object and get the contained data.

The Manual is here: http://download.oracle.com/javase/6/docs/jre/api/net/httpserver/spec/com/sun/net/httpserver/HttpExchange.html#getAttribute%28java.lang.String%29

How can i access the Object? Which methods does it have?

Umesh K · Answer 1 · 2011-04-12T09:13:14.440

2

Use Java Reflection. Using reflection you could do something like this

 Class c = Class.forName("YourClassName");
   Method m[] = c.getDeclaredMethods();
   for (int i = 0; i < m.length; i++)
   System.out.println(m[i].toString()); //iterate through these methods to find out data

edited Apr 12 '11 at 09:13

answered Apr 12 '11 at 08:47

Umesh K

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doesnt that code invoke the method "doSomething"? My Problem is that the Object contains the Data and i have no clue how it is stored in the Object or how to get it out, so i dont know a name of a function – Flo Apr 12 '11 at 09:07
@Flo see edited answer and go through the link I gave you will know how to get all data from your class. – Umesh K Apr 12 '11 at 09:14
Don't you think, you still need to know what this m[i] method do and how to deal with the return type of the Method – Premraj Apr 13 '11 at 06:14

ewan.chalmers · Accepted Answer · 2011-04-12T09:11:00.257

2

I am not familiar with this API, but it appears that HttpExchange.getAttribute is not the method you would use to get POST parameters. Rather it is a mechanism for sharing information within a chain of Filters. Since you would implement the Filters, you would document and understand the attributes that can be stored.

To read the POST details, wouldn't you do HttpExchange.getRequestBody?

edited Apr 12 '11 at 09:11

answered Apr 12 '11 at 08:54

ewan.chalmers

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score 0 · Answer 3 · answered Apr 12 '11 at 09:13

The HttpExchange returns you the type Object for the given attribute name, It is assumed that the one who try to retrieve the attribute knows the type of the attribute and can downcast the Object to appropriate class. E.g. -

String attrValue = (String) httpExchangeObject.getAttribute("nameOfTheAttribute");

you don't need to use reflection on the returned object to find out the structre.. I feel simple down-casting should solve the purpose.

score 0 · Answer 4 · answered Apr 12 '11 at 09:15

I'm not familiar with this API either. The request POST parameters should be available in raw, unparsed form from getResponseBody(). However, if you know that the getAttribute method will contain the data you need, but you don't know which class it will have (I don't know how you would know the former without knowing the latter, but anyway), you can use reflection to print the name of the class:

System.out.println (foo.getAttribute("name").getClass ());

If it turns out to be an internal, undocumented class, you can then use more reflection (or other techniques) to look at the class hierarchy until you find a publicly-documented class or interface that you can use.

But this shouldn't be necessary because what you need should be documented somewhere.

How do i find out the Structure of a Java Object?

4 Answers4