java的json使用需要用到6个工具包，
json-lib-2.3-jdk15.jar | Jakarta commons-lang 2.5 | Jakarta commons-beanutils 1.8.0 | Jakarta commons-collections 3.2.1 | Jakarta commons-logging 1.1.1 | ezmorph 1.0.6
其中json-lib-2.3-jdk15.jar为主包，其它5个为依赖包：
下面分别介绍，json格式与其他数据格式的转换
1. 数组与List转JSON
说明：使用JSONArray.fromObject()方法
1）数组
private static void arrayToJson() {
String[] arr = {"123", "abc", "3edd", "feh"};
JSONArray jsonArr = JSONArray.fromObject(arr);
System.out.println(jsonArr.toString());
}
output:
["123","abc","3edd","feh"]
2）List
private static void listToJson() {
List<People> peoples = new ArrayList<People>();
People p1 = new People("小明", "男");
People p2 = new People("小桃", "女");
peoples.add(p1);
peoples.add(p2);
JSONArray jsonArr = JSONArray.fromObject(peoples);
System.out.println(jsonArr.toString());
}
output:
[{"name":"小明","sex":"男"},{"name":"小桃","sex":"女"}]
People类
public class People {
private String name;
private String sex;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
public People(String name, String sex) {
this.name = name;
this.sex = sex;
}
}
附：注意要重写变量的set和get方法。
2. 对象和map转json
说明：使用JSONObject.fromObject()方法
1）对象
private static void objectToJson() {
People p1 = new People("小明", "男");
JSONObject jsonObj = JSONObject.fromObject(p1);
System.out.println(jsonObj.toString());
}
output:
{"name":"小明","sex":"男"}
2）Map
private static void mapToJson() {
Map<String, String> map = new HashMap<String, String>();
map.put("随遇而安", "孟非的人生经历");
map.put("浪潮之巅", "讲诉互联网公司的兴衰与变革");
JSONObject jsonObj = JSONObject.fromObject(map);
System.out.println(jsonObj.toString());
}
output:
{"随遇而安":"孟非的人生经历","浪潮之巅":"讲诉互联网公司的兴衰与变革"
3. 将json字符串转换为对象
说明：使用JSONObject.toBean()方法
private static void jsonToObj() {
String jsonStr = "{\"name\":\"小明\",\"sex\":\"男\"}";
JSONObject jsonObj = JSONObject.fromObject(jsonStr);
People p = (People)JSONObject.toBean(jsonObj, People.class);
System.out.println("name: "+p.getName()+"/sex: "+p.getSex());
}
output:
name: 小明/sex: 男
附：运行时我这边出现：java.lang.NoSuchMethodException: json.People.<init>()错误
原因是没有People()构造方法，即必须加一个空的构造方法
4. json字符串的解析
虽然json字符串直接可以映射到具体的对象，但也可以直接解析出json格式，再封装成一个对象
在People加上一个变量：friends, 类型为List<People>，为其增加set，get方法
private static void parseJsonStr() {
People p1 = new People("小明", "男");
List<People> friends = new ArrayList<People>();
People f1 = new People("小朱", "男");
People f2 = new People("小桃", "女");
friends.add(f1);
friends.add(f2);
p1.setFriends(friends);
JSONObject jsonObj = JSONObject.fromObject(p1);
System.out.println(jsonObj.toString());
String jsonStr = jsonObj.toString();
JSONObject obj = JSONObject.fromObject(jsonStr);
People p = (People)JSONObject.toBean(obj, People.class);
System.out.println("name: "+p.getName()+"/sex: "+p.getSex()+"/friends: "+p.getFriends());
}
说明：上面的一种方式是直接通过toBean方法，转换为people对象，
当然还可以直接解析，如下：
private static void parseJsonStr() {
String jsonStr = "{\"friends\":[{\"friends\":[],\"name\":\"小朱\",\"sex\":\"男\"},{\"friends\":[],\"name\":\"小桃\",\"sex\":\"女\"}],\"name\":\"小明\",\"sex\":\"男\"}";
JSONObject obj = JSONObject.fromObject(jsonStr);
People p = new People();
p.setName(obj.getString("name"));
p.setSex(obj.getString("sex"));
JSONArray jsonArr = obj.getJSONArray("friends");
List<People> friends = new ArrayList<People>();
for(int i=0;i<jsonArr.size();i++) {
People f = new People();
f.setName(jsonArr.getJSONObject(i).getString("name"));
f.setSex(jsonArr.getJSONObject(i).getString("sex"));
friends.add(f);
}
p.setFriends(friends);
System.out.println("name: "+p.getName()+"/sex: "+p.getSex()+"/friends: "+JSONArray.fromObject(p.getFriends()).toString());
}
