JSON基础：fastjson使用说明

妖狐艹你老母 2023-02-16 05:49 7阅读 0赞

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Fastjson虽然最近频爆问题，但是作为Json使用较为广泛的库，与Gson、Jackson一起仍然是众多开发者的重要选择，即使出于安全的角度考虑，从了解fastjson的使用方式以便替换的角度，也需要了解一下fastjson的使用方式，这篇文章进行简单的总结和整理。

# maven引用 #

使用1.2.70版本是官方目前对于2020年度发现的0-day漏洞的对应的解决方案，建议使用此版或者更新的版本。

<dependency>
        <groupId>com.alibaba</groupId>
        <artifactId>fastjson</artifactId>
        <version>1.2.70</version>
    </dependency>

# 三个类 #

fastjson中主要有三个类：

*  JSON
 *  JSONObject
 *  JSONArray

说明：JSONObject和JSONArray均继承于JSON类，JSON类本身为一个抽象类，JSONObject用于json对象处理，JSONArray用于json对象数组处理，由于JSON本身为抽象类，所以其无法通过实例化来进行相应操作，主要通过其静态函数进行相关的parse转化操作。

# 使用示例 #

> 整体说明：三个主要的类中，JSON主要通过使用其静态函数进行转换，比如从字符串到Json对象，从Json对象到字符串。JSONObject用于处理Json类，JSONArray用于处理Json数组，就像Json可以组合一样JSONArray和JSONObject也可以同样组成复杂的Json结构。

*  JSON定义

public abstract class JSON implements JSONStreamAware, JSONAware {

*  JSONObject定义

public class JSONObject extends JSON implements Map<String, Object>, Cloneable, Serializable, InvocationHandler {

*  JSONArray定义

public class JSONArray extends JSON implements List<Object>, Cloneable, RandomAccess, Serializable {

## 示例1: Json对象和字符串 ##

*  示例代码

final String JSON_PERSON_STRING = "{\"name\":\"liumiao\",\"id\":1001}";
            final JSONObject json = JSON.parseObject(JSON_PERSON_STRING);
            System.out.println("name: " + json.get("name") + " id:" + json.get("id"));
            System.out.println(JSON.toJSONString(json));

*  执行结果

name: liumiao id:1001
    { "name":"liumiao","id":1001}

## 示例2: Json数组和字符串 ##

*  示例代码

final String JSON_PERSONS_STRING = "[{\"name\":\"liumiao\",\"id\":1001},{\"name\":\"miaoliu\",\"id\":1002}]";
            final JSONArray jsons = JSON.parseArray(JSON_PERSONS_STRING);
            System.out.println(JSON.toJSONString(jsons));
    
            System.out.println("loop using size()");
            for(int i=0; i<jsons.size(); i++){ 
                JSONObject json = jsons.getJSONObject(i);
                System.out.println("name: " + json.get("name") + " id:" + json.get("id"));
            }
    
            System.out.println("loop using iterator");
            Iterator<Object> iterator = jsons.iterator();
            while(iterator.hasNext()) { 
                JSONObject json = (JSONObject) iterator.next();
                System.out.println("name: " + json.get("name") + " id:" + json.get("id"));
            }

*  执行结果

[{ "name":"liumiao","id":1001},{ "name":"miaoliu","id":1002}]
    loop using size()
    name: liumiao id:1001
    name: miaoliu id:1002
    loop using iterator
    name: liumiao id:1001
    name: miaoliu id:1002

## 示例3: Json组合结构和字符串 ##

*  示例代码

final String JSON_PERSONS_STRING = "[{\"name\":\"liumiao\",\"id\":1001,\"courses\":" +
                    "[{\"course\":\"math\",\"score\":90},{\"course\":\"english\",\"score\":80}]}," +
                    "{\"name\":\"miaoliu\",\"id\":1002,,\"courses\":" +
                    "[{\"course\":\"math\",\"score\":80},{\"course\":\"english\",\"score\":90}]}]";
    
            final JSONArray jsons = JSON.parseArray(JSON_PERSONS_STRING);
            System.out.println(JSON.toJSONString(jsons));
    
            System.out.println("loop using size()");
            for (int i = 0; i < jsons.size(); i++) { 
                JSONObject json = jsons.getJSONObject(i);
                System.out.println("name: " + json.get("name") + " id:" + json.get("id"));
                JSONArray courses = json.getJSONArray("courses");
                for(int j=0; j<courses.size(); j++) { 
                    JSONObject course = courses.getJSONObject(j);
                    System.out.println("course: " + course.get("course") + " score:" + course.get("score"));
                }
            }
    
            System.out.println("loop using iterator");
            Iterator<Object> iterator = jsons.iterator();
            while (iterator.hasNext()) { 
                JSONObject json = (JSONObject) iterator.next();
                System.out.println("name: " + json.get("name") + " id:" + json.get("id"));
    
                JSONArray courses = json.getJSONArray("courses");
                Iterator<Object> courseIterator = courses.iterator();
                while(courseIterator.hasNext()){ 
                    JSONObject course = (JSONObject) courseIterator.next();
                    System.out.println("course: " + course.get("course") + " score:" + course.get("score"));
                }
            }

*  执行结果

[{ "courses":[{ "score":90,"course":"math"},{ "score":80,"course":"english"}],"name":"liumiao","id":1001},{ "courses":[{ "score":80,"course":"math"},{ "score":90,"course":"english"}],"name":"miaoliu","id":1002}]
    loop using size()
    name: liumiao id:1001
    course: math score:90
    course: english score:80
    name: miaoliu id:1002
    course: math score:80
    course: english score:90
    loop using iterator
    name: liumiao id:1001
    course: math score:90
    course: english score:80
    name: miaoliu id:1002
    course: math score:80
    course: english score:90

## 示例4: Json对象和JavaBean ##

*  示例代码

public class Person { 
        private int id;
        private String name;
    
        public int getId() { 
            return id;
        }
    
        public void setId(int id) { 
            this.id = id;
        }
    
        public String getName() { 
            return name;
        }
    
        public void setName(String name) { 
            this.name = name;
        }
    
        public Person(int id, String name) { 
            this.id = id;
            this.name= name;
        }
    }

转化示例代码

final String JSON_PERSON_STRING = "{\"name\":\"liumiao\",\"id\":1001}";
            final JSONObject json = JSON.parseObject(JSON_PERSON_STRING);
            String name = json.getString("name");
    
            System.out.println("name: " + json.get("name") + " id:" + json.get("id"));
            // using new
            Person person1 = new Person(json.getInteger("id"),json.getString("name"));
            System.out.println(JSON.toJSONString(person1));
    
            // using JSON.parsObject
            Person person2 = JSON.parseObject(JSON_PERSON_STRING, Person.class);
            System.out.println(JSON.toJSONString(person2));
    
            // using JSON.parsObject
            Person person3 = JSON.parseObject(JSON_PERSON_STRING, new TypeReference<Person>() {});
            System.out.println(JSON.toJSONString(person3));

*  执行结果

name: liumiao id:1001
    { "id":1001,"name":"liumiao"}
    { "id":1001,"name":"liumiao"}
    { "id":1001,"name":"liumiao"}

## 示例5: Json数组和JavaBean ##

*  示例代码

final String JSON_PERSONS_STRING = "[{\"name\":\"liumiao\",\"id\":1001},{\"name\":\"miaoliu\",\"id\":1002}]";
            final JSONArray jsons = JSON.parseArray(JSON_PERSONS_STRING);
            System.out.println(JSON.toJSONString(jsons));
    
            List<Person> personList1 = new ArrayList<Person>();
            Iterator<Object> iterator = jsons.iterator();
    
            while(iterator.hasNext()) { 
                JSONObject json = (JSONObject) iterator.next();
                personList1.add(new Person(json.getInteger("id"),json.getString("name")));
            }
            System.out.println(JSON.toJSONString(personList1));
    
            List<Person> personList2 = JSON.parseArray(JSON_PERSONS_STRING,Person.class);
            System.out.println(JSON.toJSONString(personList2));
    
            List<Person> personList3 = JSON.parseObject(JSON_PERSONS_STRING, new TypeReference<ArrayList<Person>>() { });
            System.out.println(JSON.toJSONString(personList3));
    
            List<Person> personList4 = new ArrayList<Person>();
            personList4.add(new Person(2001,"liu"));
            personList4.add(new Person(2002,"miao"));
            personList4.add(new Person(2003,"liumiao"));
            System.out.println(JSON.toJSONString(personList4));

*  执行结果

[{ "name":"liumiao","id":1001},{ "name":"miaoliu","id":1002}]
    [{ "id":1001,"name":"liumiao"},{ "id":1002,"name":"miaoliu"}]
    [{ "id":1001,"name":"liumiao"},{ "id":1002,"name":"miaoliu"}]
    [{ "id":1001,"name":"liumiao"},{ "id":1002,"name":"miaoliu"}]
    [{ "id":2001,"name":"liu"},{ "id":2002,"name":"miao"},{ "id":2003,"name":"liumiao"}]

## 示例6: Json组合结构和JavaBean ##

*  示例代码

public class Person {
        private int id;
        private String name;
        private List<Course> courses;
    
        public List<Course> getCourses() {
            return courses;
        }
    
        public void setCourses(List<Course> courses) {
            this.courses = courses;
        }
    
        public int getId() {
            return id;
        }
    
        public void setId(int id) {
            this.id = id;
        }
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public Person(int id, String name, List<Course> courses) {
            this.id = id;
            this.name= name;
            this.courses=courses;
        }
    }
    
    public class Course {
        private String course;
        private int score;
    
        public String getCourse() {
            return course;
        }
    
        public void setCourse(String course) {
            this.course = course;
        }
    
        public int getScore() {
            return score;
        }
    
        public void setScore(int score) {
            this.score = score;
        }
    }

final String JSON_PERSON_STRING = "{\"name\":\"liumiao\",\"id\":1001,\"courses\":" +
                    "[{\"course\":\"math\",\"score\":90},{\"course\":\"english\",\"score\":80}]}";
    
            final JSONObject json = JSON.parseObject(JSON_PERSON_STRING);
            System.out.println(JSON.toJSONString(json));
    
            Person person1 = JSON.parseObject(JSON_PERSON_STRING, Person.class);
            System.out.println(JSON.toJSONString(person1));
    
            Person person2 = JSON.parseObject(JSON_PERSON_STRING,new TypeReference<Person>() { });
            System.out.println(JSON.toJSONString(person2));

*  执行结果

{ "courses":[{ "score":90,"course":"math"},{ "score":80,"course":"english"}],"name":"liumiao","id":1001}
    { "courses":[{ "course":"math","score":90},{ "course":"english","score":80}],"id":1001,"name":"liumiao"}
    { "courses":[{ "course":"math","score":90},{ "course":"english","score":80}],"id":1001,"name":"liumiao"}

# 参考内容 #

https://github.com/alibaba/fastjson  
https://github.com/alibaba/fastjson/wiki/Quick-Start-CN  
https://mvnrepository.com/artifact/com.alibaba/fastjson/

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