JSON基础：fastjson使用说明

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。

com.alibabafastjson1.2.70

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, Cloneable, Serializable, InvocationHandler {

• JSONArray定义

public class JSONArray extends JSON implements List, 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() {});
        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 Listcourses;

    public ListgetCourses() {
        return courses;
    }

    public void setCourses(Listcourses) {
        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, Listcourses) {
        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/