Another Json result type(struts2jsonresult)

Name	struts2jsonresult
Publisher
License	Apache License 2.0
Version	0.99(release candidate)
Compatibility	Struts 2.0.2+
Homepage	http://code.google.com/p/struts2jsonresult/
Download	http://code.google.com/p/struts2jsonresult/downloads/list

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Overview

This struts2 plugin simply provide a new result type: 'json', as an alternative to struts2 json plugin. It provide better flexibility to specify what properties of a Java Bean to be serialized, and it works well with spring and hibernate.

Features

The target to be serialized can be specified by the target parameter.(If not specified, the action itself will be serialized.)
Multiple include and exclude patterns can be applied to control what to be serialized of a bean, and how deep to be serialized.
The output json string can be well formatted by specifying the prettyPrint parameter with a true value
The status code of the HTTP response can be specified. This is convenient for the client to handle the error properly.
So do the content type and character encoding.
jsonp support
A parameter named noCache can be specified to disable IE's buggy cache.
Gzip support for content encoding.

Usage

Put the following jars together with struts2jsonresult.jar in your WEB-INF/lib directory.

common logging, the logger name is the same as the class name
flexjson 1.7

Example

In struts2.xml, define a package that extends struts-default and set the result type json as default.

Define your action in your struts2.xml

<action name="listByStudent" class="articleAction" method="listByStudent"> <result>  <param name="target">result</param> <param name="patterns"> -*.class, -gradeArticle </param> </result> </action>

And the java code of your Action file:

public class ArticleAction { private Article article; private Object result; public String listByStudent() { this.result = ....//find from database, return as an list return Action.SUCCESS; } public Object getResult() { return result; } public Article getArticle() { return article; } }

Patterns

You can set the parameter named "patterns" to include or exclude some properties of the bean to be serialized.

Use '+' as include, and '-' as exclude.
For example

<action name="listByStudent" class="articleAction" method="listByStudent"> <result> <param name="patterns"> -*.class, -gradeArticle </param> </result> </action>

the patterns will be translated to

new JSONSerializer().exclude("*.class").exclude("gradeArticle").

About how to use patterns in flexjson, refer to http://flexjson.sourceforge.net/ and the javadoc of JSONSerializer

Parameters

Following parameters can be set.

Parameter name	Default value	Description
target	null	the bean to be serialized, if set to null, the action itself will be serialized.
patterns	null	Fully support the patterns that can be applied to flexjson. See the above section about "Patterns"
prettyPrint	false	whether to format the result json string
rootName	null	if set, it will wrap the resulting JSON in a javascript object that contains a single field named rootName.
deepSerialize	false	whether to deep serialize the object, by default flexjson will not serialize the collections in a bean
out.contentType	application/json	http reponse content type
out.statusCode	200	http status code of the response, sometimes 500 maybe used to indicate an exception
out.characterEncoding	utf-8	http response character encoding
out.gzip	false	whether to use gzip to compress the response, to reduce the network transfer load
out.noCache	false	when set to true, the following 3 headers will be set. Cache-Control set to no-cache, Expires set to 0 and Pragma set to No-cache
prefix	false	when set to true, a prefix "{}&&" would be added before the json result, this is to prevent json attack, see this blog for the detail
callbackParameter	null	when set, the result will be wrapped with a function. The function name is speicified by this callbackParameter. For example: when callbackParameter is set to callback, http://localhost:9080/spiderx/test/test?callback=alert will generate a result like alert({ ....});

Exception Handling

You can define some global exception mapping in your struts.xml. when exception is thrown, an special status code can be used, and the client can deal with different exception type by the status code.

For example:

<package name="json" extends="struts-default"> <result-types> <result-type name="json" default="true" class="code.google.struts2jsonresult.JSONResult"> <param name="target">result</param> <param name="out.gzip">true</param> <param name="prettyPrint">true</param> </result-type> </result-types> <global-results> <result name="RuntimeException" type="json"> <param name="out.statusCode">500</param> <param name="target">exception</param> <param name="patterns">+class,+message,-*</param> </result> <result name="ApplicationException" type="json"> <param name="out.statusCode">501</param> <param name="target">exception</param> <param name="patterns">+class,+message,-*</param> </result> </global-results> <global-exception-mappings> <exception-mapping exception="com.tdyc.spider.ApplicationException" result="ApplicationException" /> <exception-mapping exception="java.lang.RuntimeException" result="RuntimeException" /> </global-exception-mappings> </package>

Now when an exception occurs, for example a NullPointerException, following json will be the output with a status code 500:

"class": "java.lang.NullPointerException", "message": null }

Notice the patterns for flexjson:

The first expression to match a path that action will be taken thus short circuiting all other expressions defined later.

so for "+class,+message,-*", only the class and message properties are included.

Version History

Version	Date	Author	Notes
0.99	Mar 6, 2009		Initial release candidate

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