JSON--List集合转换成JSON对象_JAVA_编程开发_程序员俱乐部

转发出处：http://www.cnblogs.com/xmaomao/p/3184542.html

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1. 简单的手动放置 键值对 到JSONObject，然后在put到JSONArray对象里

List<Article> al = articleMng.find(f);
??????????? System.out.println(al.size());
??????????? HttpServletResponse hsr = ServletActionContext.getResponse();
??????????? if(null == al){
??????????????? return ;
??????????? }
??????????? for(Article a : al){
??????????????? System.out.println(a.getId()+a.getDescription()+a.getTitle());
??????????? }
??????????? JSONArray json = new JSONArray();
??????????? for(Article a : al){
??????????????? JSONObject jo = new JSONObject();
??????????????? jo.put("id", a.getId());
??????????????? jo.put("title", a.getTitle());
??????????????? jo.put("desc", a.getDescription());
??????????????? json.put(jo);
??????????? }
??????????? try {
??????????????? System.out.println(json.toString());
??????????????? hsr.setCharacterEncoding("UTF-8");
??????????????? hsr.getWriter().write(json.toString());
??????????? } catch (IOException e) {
??????????????? e.printStackTrace();
??????????? }

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上述代码JSONArray是引入的org.json.JSONArray包

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而用net.sf.json包下JSONArray的静态方法：fromObject(list) 这是网上大多是都是直接用此方法快捷转换JSON，但是对于Hibernate级联操作关联的对象，这个方法就会报错，如果将映射文件中的级联配置去掉就行了。

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另外对于list的要求就是其中的元素是字符串或对象，否则JSON不知道你想要的是什么数据。

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<many-to-one name="cmsent" column="comment_tid" class="com.fcms.cms.entity.CmsComment" 
        not-null="false" cascade="delete">

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但是级联操作毕竟还是得存在，否则以后数据冗余、多余。

解决方法就是：JSONArray subMsgs = JSONArray.fromObject(object, config);

JsonConfig config = new JsonConfig();
??????? config.setJsonPropertyFilter(new PropertyFilter() {
??????????? public boolean apply(Object arg0, String arg1, Object arg2) {
???????????????? if (arg1.equals("article") ||arg1.equals("fans")) {
??????????????????????? return true;
??????????????????? } else {
??????????????????????? return false;
??????????????????? }
??????????? }
??????? });

说明：提供了一个过滤作用，如果遇到关联的对象时他会自动过滤掉，不去执行关联关联所关联的对象。这里我贴出我hibernate中的配置关系映射的代码帮助理解：

<!-- 配置话题和团体之间的关系 -->
??????? <many-to-one name="article" class="com.fcms.nubb.article" column="article_id"/>
???????
??????? <!-- 配置主题帖与回复的帖子之间的关系 -->
??????? <set name="subMessages" table="sub_message" inverse="true" cascade="all" lazy="false" order-by="date asc">
??????????? <key column="theme_id" />
??????????? <one-to-many class="bbs.po.SubMessage" />
??????? </set>

总结：

1. JSONArray subMsgs = JSONArray.fromObject(subMessages, config);其中config是可选的，当出现上面的情况是可以配置config参数，如果没有上面的那种需求就可以直接使用fromObject(obj)方法，它转换出来的就是标准的json对象格式的数据，如下：

{["attr", "content", ...}, ...]}

2. JSONObject jTmsg = JSONObject.fromObject(themeMessage, config);这是专门用来解析标准的pojo，或者map对象的，pojo对象的格式就不用说了，map的形式是这样的{"str", "str"}。

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----------------------------------------------------------- ?分割 -------------------------------------------------------------------------------------------

?对于JSONArray和JSON之前用到想吐了！！！

但是，最近发现个好东西--fastjson (阿里巴巴温少写的一个将Object转为json数据的工具包)

Binary : http://code.alibabatech.com/mvn/releases/com/alibaba/fastjson/1.1.1/fastjson-1.1.1.jar
Source :http://code.alibabatech.com/mvn/releases/com/alibaba/fastjson/1.1.1/fastjson-1.1.1-sources.jar
Subversion : http://code.alibabatech.com/svn/fastjson/

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bean

package com.nubb.bean;

import java.io.Serializable;

public class Person implements Serializable{
??? private static final long serialVersionUID = 1L;
??? private String name;
??? private int age;
??? private String address;
??? public String getName() {
??????? return name;
??? }
??? public void setName(String name) {
??????? this.name = name;
??? }
??? public int getAge() {
??????? return age;
??? }
??? public void setAge(int age) {
??????? this.age = age;
??? }
??? public String getAddress() {
??????? return address;
??? }
??? public void setAddress(String address) {
??????? this.address = address;
??? }
???
???
}

JsonUtil

package com.nubb.test;

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.StandardOpenOption;
import java.util.ArrayList;
import java.util.List;

import com.alibaba.fastjson.JSON;
import com.nubb.bean.Person;

public class JSONSerializer {
??????? private static final String DEFAULT_CHARSET_NAME = "UTF-8";

??????? public static <T> String serialize(T object) {
??????????? return JSON.toJSONString(object);
??????? }

??????? public static <T> T deserialize(String string, Class<T> clz) {
??????????? return JSON.parseObject(string, clz);
??????? }

??????? public static <T> T load(Path path, Class<T> clz) throws IOException {
??????????? return deserialize(
??????????????????? new String(Files.readAllBytes(path), DEFAULT_CHARSET_NAME), clz);
??????? }

??????? public static <T> void save(Path path, T object) throws IOException {
??????????? if (Files.notExists(path.getParent())) {
??????????????? Files.createDirectories(path.getParent());
??????????? }
??????????? Files.write(path,
??????????????????? serialize(object).getBytes(DEFAULT_CHARSET_NAME),
??????????????????? StandardOpenOption.WRITE,
??????????????????? StandardOpenOption.CREATE,
??????????????????? StandardOpenOption.TRUNCATE_EXISTING);
??????? }
???????
??????? public static void main(String[] args) {
??????????? Person person1 = new Person();
??????????? person1.setAddress("address");
??????????? person1.setAge(11);
??????????? person1.setName("amao");
???????????
??????????? Person person2 = new Person();
??????????? person2.setAddress("address");
??????????? person2.setAge(11);
??????????? person2.setName("amao");
???????????
??????????? List<Person> lp = new ArrayList<Person>();
??????????? lp.add(person1);
??????????? lp.add(person2);
??????????? System.out.println(serialize(lp));
??????? }
???????
}

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输出：

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[{"address":"address","age":11,"name":"amao"},{"address":"address","age":11,"name":"amao"}]

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