使用Struts 2将Java对象序列化成JSON

Struts 2有个很强大的功能，就是可以自动完成服务器端Java对象和客户端JSON对象之间的映射。这篇文章就介绍一下如何将Java对象序列化成JSON格式并传到客户端。可以看看不同的Java类型和JSON类型之间是如何映射的。

 

pom.xml

需要引入struts2-json-plugin包。

<dependencies><dependency><groupId>org.apache.struts</groupId><artifactId>struts2-core</artifactId><version>2.3.12</version></dependency><dependency><groupId>org.apache.struts</groupId><artifactId>struts2-json-plugin</artifactId><version>2.3.12</version></dependency></dependencies>

struts.xml

package extends要增加”json-default”；负责映射的TestAction设置result type为json。

<package name="sandbox" namespace="/" extends=" struts-default, json-default"><action name="main" class="sandbox.z.MainAction"><result>/jsp/main.jsp</result></action><action name="test" class="sandbox.z.TestAction"><result type="json" /></action></package>

main.jsp

<script>require([ "dojo/ready",           "dojo/_base/xhr",           "dojo/json",          "dijit/registry" ], function(ready, xhr, JSON, registry) {ready(function() {var xhrArgs = {url : "/test.action",handleAs : "json", /*设置返回数据的类型，和服务器端的设置一致*/sync : true};var deferred = xhr.get(xhrArgs);deferred.then(function(result) {var output = JSON.stringify(result); /*将返回值变成json string*/console.log(output); /*打印到Firebug console*/});});});</script>

TestAction.java

TestAction中，凡是有setter方法的属性都会被转换成JSON并输出到客户端。

package sandbox.z;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;import com.opensymphony.xwork2.ActionSupport;public class TestAction extends ActionSupport {private static final long serialVersionUID = 1L;private String name = "john";private int age = 30;private double height = 1.78;private int[] scores = {85, 90};private List<Integer> score_array = new ArrayList<Integer>();public void setScore_array(List<Integer> score_array) {this.score_array = score_array;}public List<Integer> getScore_array() {return score_array;}private List array = new ArrayList();public List getArray() {return array;}public void setArray(List array) {this.array = array;}private Map books_map = new HashMap();public void setBooks_map(Map books_map) {this.books_map = books_map;}public Map getBooks_map() {return books_map;}private Book book = new Book();public void setBook(Book book) {this.book = book;}public Book getBook() {return book;}public String execute() {score_array.add(85);score_array.add(90);array.add(85);array.add("Struts2");books_map.put("struts2", 85);getBook().setName("Struts2");getBook().setPrice(85.30);List<String> sellers = new ArrayList<String>();sellers.add("SA");sellers.add("SB");getBook().setSellers(sellers);return SUCCESS;}public void setName(String name) {this.name = name;}public String getName() {return name;}public void setAge(int age) {this.age = age;}public int getAge() {return age;}public void setHeight(double height) {this.height = height;}public double getHeight() {return height;}public void setscores(int[] scores) {this.scores = scores;}public int[] getscores() {return scores;}}

Firebug console

{"age":30,"array":[85,"Struts2"],"book":{"name":"Struts2","price":85.3,"sellers":["SA","SB"]},"books_map":{"struts2":85},"height":1.78,"name":"john","score_array":[85,90],"scores":[85,90]

总结

可以看到，从JAVA对象转换到JSON格式还是非常直白的。由于JAVA对象比较复杂，表达能力强，而JSON格式比较简单，表达能力弱，因此这种转换大致不太会出错。而相反的，如果要将JSON转换成JAVA，则需要考虑是否需要额外的信息帮助将简单的格式转换成复杂对象。可以想象这中间会出现歧义。

参考文献

[1] JSON Plugin. http://struts.apache.org/release/2.2.x/docs/json-plugin.html