Json工具类用法

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一，字符串转JSON对象

marketingActivityPO.getRuleContent（）字符串类型数据格式如下：

{
    "activityName":"测试",
    "merchantsId":"",
    "storeId":"",
    "activityGuideWords":"",
    "ruleContent":{
        "fType":3,
        "randomDown":"0.1",
        "randomUp":"0.5",
        "feeUnit":"2",
        "feeNum":[
            {
                "fee":"100"
            }
        ],
        "grabTime":[
            {
                "beginTime":"10",
                "endTime":"22"
            }
        ],
        "joinNum":"100"
    },
    "outActCode":"7520180622",
    "expTime":"20180630",
    "activityWhiteListFileId":102,
    "activityBlackListFileId":90
}

com.alibaba.fastjson.JSONObject jsonObject = 
com.alibaba.fastjson.JSONObject.parseObject(marketingActivityPO.getRuleContent());
String activityBlackListFileId = jsonObject.getString("activityBlackListFileId");

2，JSON字符串转地图

修改JSON字符串的值之后使用同时杰克逊的ObjectMapper的writeValueAsString方法可以把Java的对象转化成JSON字符串

Map<String,String> value = JSON.parseObject(marketingActivityPO.getRuleContent(), Map.class);
value.put("activityBlackListFileId", fileId+"");
ObjectMapper json = new ObjectMapper();
String newRuleContent = "";
try {
	newRuleContent = json.writeValueAsString(value);
} catch (JsonProcessingException e) {
	e.printStackTrace();
}

JSON.parseObject，是将Json的字符串转化为相应的对象; JSON.toJSONString则是将对象转化为Json的字符串

public class jsonTest {
    public static void main(String[] args) {
        /**
         * json字符串转化为对象
         */
        String jsonString = "{name:'Antony',age:'12',sex:'male',telephone:'88888'}";
        Staff staff = JSON.parseObject(jsonString, Staff.class);
        System.out.println(staff.toString());//Staff{name='Antony', age=12, sex='male', birthday=null}

        /**
         * 对象转化为json字符串
         */
        String jsonStr = JSON.toJSONString(staff);
        System.out.println(jsonStr);//{"age":12,"name":"Antony","sex":"male"}
    }
}

3，JSON案例

首先定义三个字符串

//json字符串-简单对象型
private static final String  JSON_OBJ_STR = "{\"studentName\":\"lily\",\"studentAge\":12}";
//json字符串-数组类型
private static final String  JSON_ARRAY_STR = "[{\"studentName\":\"lily\",\"studentAge\":12},{\"studentName\":\"lucy\",\"studentAge\":15}]";
//复杂格式json字符串
private static final String  COMPLEX_JSON_STR = "{\"teacherName\":\"crystall\",\"teacherAge\":27,\"course\":{\"courseName\":\"english\",\"code\":1270},\"students\":[{\"studentName\":\"lily\",\"studentAge\":12},{\"studentName\":\"lucy\",\"studentAge\":15}]}";

示例1：JSON格式字符串与JSON对象之间的转换。

示例1.1 JSON字符串 - 简单对象型与JSONObject的之间的转换

/**
     * json字符串-简单对象型与JSONObject之间的转换
     */
    public static void testJSONStrToJSONObject(){

        JSONObject jsonObject = JSON.parseObject(JSON_OBJ_STR);
        //JSONObject jsonObject1 = JSONObject.parseObject(JSON_OBJ_STR); //因为JSONObject继承了JSON，所以这样也是可以的

        System.out.println(jsonObject.getString("studentName")+":"+jsonObject.getInteger("studentAge"));

    }

示例1.2 JSON字符串 - 数组类型与JSONArray之间的转换

/**
     * json字符串-数组类型与JSONArray之间的转换
     */
    public static void testJSONStrToJSONArray(){

        JSONArray jsonArray = JSON.parseArray(JSON_ARRAY_STR);
        //JSONArray jsonArray1 = JSONArray.parseArray(JSON_ARRAY_STR);//因为JSONArray继承了JSON，所以这样也是可以的

        //遍历方式1
        int size = jsonArray.size();
        for (int i = 0; i < size; i++){
            JSONObject jsonObject = jsonArray.getJSONObject(i);
            System.out.println(jsonObject.getString("studentName")+":"+jsonObject.getInteger("studentAge"));
        }

        //遍历方式2
        for (Object obj : jsonArray) {
            JSONObject jsonObject = (JSONObject) obj;
            System.out.println(jsonObject.getString("studentName")+":"+jsonObject.getInteger("studentAge"));
        }
    }

示例1.3-复杂的JSON格式字符串与JSONObject的之间的转换

/**
     * 复杂json格式字符串与JSONObject之间的转换
     */
    public static void testComplexJSONStrToJSONObject(){

        JSONObject jsonObject = JSON.parseObject(COMPLEX_JSON_STR);
        //JSONObject jsonObject1 = JSONObject.parseObject(COMPLEX_JSON_STR);//因为JSONObject继承了JSON，所以这样也是可以的
        
        String teacherName = jsonObject.getString("teacherName");
        Integer teacherAge = jsonObject.getInteger("teacherAge");
        JSONObject course = jsonObject.getJSONObject("course");
        JSONArray students = jsonObject.getJSONArray("students");

    }

示例2：JSON格式字符串与的javaBean之间的转换。

首先，我们针对数据源所示的字符串，提供三个的javaBean。

public class Student {

    private String studentName;
    private Integer studentAge;

    public String getStudentName() {
        return studentName;
    }

    public void setStudentName(String studentName) {
        this.studentName = studentName;
    }

    public Integer getStudentAge() {
        return studentAge;
    }

    public void setStudentAge(Integer studentAge) {
        this.studentAge = studentAge;
    }
}

public class Course {

    private String courseName;
    private Integer code;

    public String getCourseName() {
        return courseName;
    }

    public void setCourseName(String courseName) {
        this.courseName = courseName;
    }

    public Integer getCode() {
        return code;
    }

    public void setCode(Integer code) {
        this.code = code;
    }
}

public class Teacher {

    private String teacherName;
    private Integer teacherAge;
    private Course course;
    private List<Student> students;

    public String getTeacherName() {
        return teacherName;
    }

    public void setTeacherName(String teacherName) {
        this.teacherName = teacherName;
    }

    public Integer getTeacherAge() {
        return teacherAge;
    }

    public void setTeacherAge(Integer teacherAge) {
        this.teacherAge = teacherAge;
    }

    public Course getCourse() {
        return course;
    }

    public void setCourse(Course course) {
        this.course = course;
    }

    public List<Student> getStudents() {
        return students;
    }

    public void setStudents(List<Student> students) {
        this.students = students;
    }
}

json字符串与javaBean之间的转换推荐使用TypeReference <T>这个类，使用泛型可以更加清晰，当然也有其它的转换方式，这里就不做探讨了。

示例2.1 JSON字符串 - 简单对象型与javaBean的之间的转换

/**
     * json字符串-简单对象与JavaBean_obj之间的转换
     */
    public static void testJSONStrToJavaBeanObj(){

        Student student = JSON.parseObject(JSON_OBJ_STR, new TypeReference<Student>() {});
        //Student student1 = JSONObject.parseObject(JSON_OBJ_STR, new TypeReference<Student>() {});//因为JSONObject继承了JSON，所以这样也是可以的

        System.out.println(student.getStudentName()+":"+student.getStudentAge());

    }

示例2.2 JSON字符串 - 数组类型与javaBean的之间的转换

/**
     * json字符串-数组类型与JavaBean_List之间的转换
     */
    public static void testJSONStrToJavaBeanList(){
        
        ArrayList<Student> students = JSON.parseObject(JSON_ARRAY_STR, new TypeReference<ArrayList<Student>>() {});
        //ArrayList<Student> students1 = JSONArray.parseObject(JSON_ARRAY_STR, new TypeReference<ArrayList<Student>>() {});//因为JSONArray继承了JSON，所以这样也是可以的
        
        for (Student student : students) {
            System.out.println(student.getStudentName()+":"+student.getStudentAge());
        }
    }

示例2.3-复杂的JSON格式字符串与与javaBean的之间的转换

/**
     * 复杂json格式字符串与JavaBean_obj之间的转换
     */
    public static void testComplexJSONStrToJavaBean(){

        Teacher teacher = JSON.parseObject(COMPLEX_JSON_STR, new TypeReference<Teacher>() {});
        //Teacher teacher1 = JSON.parseObject(COMPLEX_JSON_STR, new TypeReference<Teacher>() {});//因为JSONObject继承了JSON，所以这样也是可以的
        String teacherName = teacher.getTeacherName();
        Integer teacherAge = teacher.getTeacherAge();
        Course course = teacher.getCourse();
        List<Student> students = teacher.getStudents();
    }

此外的：

1，对于JSON对象与JSON格式字符串的转换可以直接用toJSONString（）这个方法。

2的，JavaBean与JSON格式字符串之间的转换要用到：JSON.toJSONString（OBJ）;

3的，JavaBean与JSON对象间的转换使用：JSON.toJSON（OBJ），然后使用强制类型转换，的JSONObject或者JSONArray。