FastJson使用范例(Java、Scala版)

0.目录

• FastJson简介
• FastJson三个核心类
• Maven
• Java API
  • 反序列化
    • 反序列化一个简单Json字符串
    • 反序列化一个简单JSON字符串成Java对象组
    • 反序列化一个复杂的JSON字符串
  • 序列化
  • 序列化和反序列化日期
  • JsonObject的一些操作
  • jsonArray的一些操作
• Scala API
  • 反序列化
    • demo日志内容
    • 反序列化简单json字符串
    • 反序列化简单json字符串组
      • String处理
      • List处理

1. FastJson简介

JSON协议在日常开发中很常用，包括前后端的数据接口，日志字段的保存等，通常都采用JSON协议。FastJson是阿里的开源框架，很好用，估计开发的同学都有使用过。这里做一个简单的用法总结，配一些demo。除了Java版本外，由于在Spark也经常清洗日志，所以配上了Scala版本，方便日后查询使用。完整代码可以参考Github:https://github.com/tygxy/BigData

2. FastJson三个核心类

• JSON：fastjson的解析器，用于json字符串和javaBean、Json对象的转换
• JSONObject：fastJson提供的json对象
• JSONArray：fastJson提供json数组对象

3. Maven

    <dependency>
        <groupId>com.alibaba</groupId>
        <artifactId>fastjson</artifactId>
        <version>1.2.47</version>
    </dependency>

4. Java API

4.1 反序列化

• 反序列化一个简单Json字符串

  • 创建JavaBean的User类

  public class User {
      private String name;
      private int age;
  
      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;
      }
  }
  

  • 反序列化操作

  String jsonString = "{\"name\":\"张三\",\"age\":50}";
  User user= JSON.parseObject(jsonString,User.class);
  System.out.println("name:"+user.getName()+" age:"+user.getAge());
  
  // 输出结果 name:张三 age:50
  

• 反序列化一个简单JSON字符串成Java对象组

String jsonArrayString = "[{\"name\":\"张三\",\"age\":50},{\"name\":\"李四\",\"age\":51}]";
List<User> userList = JSON.parseArray(jsonArrayString,User.class);
Iterator it = userList.iterator();
while (it.hasNext()) {
    User u = (User)it.next();
    System.out.println("name:"+u.getName()+" age:"+u.getAge());
}

// 输出结果  name:张三 age:50
            name:李四 age:51

• 反序列化一个复杂的JSON字符串
  • 分别创建JavaBean的Course类、Student类、Teacher类

  public class Course {
      private String courseName;
      private String code;
  
      public Course (String courseName, String code){
          this.setCourseName(courseName);
          this.setCode(code);
      }
  
      public String getCourseName() {
          return courseName;
      }
  
      public void setCourseName(String courseName) {
          this.courseName = courseName;
      }
  
      public String getCode() {
          return code;
      }
  
      public void setCode(String code) {
          this.code = code;
      }
  }
  
  public class Student {
      private int id;
      private String studentName;
      private int age;
  
      public Student(int id, String studentName, int age) {
          this.setId(id);
          this.setStudentName(studentName);
          this.setAge(age);
      }
  
      public int getId() {
          return id;
      }
  
      public void setId(int id) {
          this.id = id;
      }
  
      public String getStudentName() {
          return studentName;
      }
  
      public void setStudentName(String studentName) {
          this.studentName = studentName;
      }
  
      public int getAge() {
          return age;
      }
  
      public void setAge(int age) {
          this.age = age;
      }
  }
  
  public class Teacher {
      private String teacherName;
      private int age;
      private Course course;
      private List<Student> students;
  
      public Teacher(String teacherName, int age, Course course, List<Student> students) {
          this.setTeacherName(teacherName);
          this.setAge(age);
          this.setCourse(course);
          this.setStudents(students);
      }
  
      public String getTeacherName() {
          return teacherName;
      }
  
      public void setTeacherName(String teacherName) {
          this.teacherName = teacherName;
      }
  
      public int getAge() {
          return age;
      }
  
      public void setAge(int age) {
          this.age = age;
      }
  
      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;
      }
  }
  

  • 反序列化操作

  String complexJsonString = "{\"teacherName\":\"crystall\",\"age\":27,\"course\":{\"courseName\":\"english\",\"code\":1270},\"students\":[{\"id\":1,\"studentName\":\"lily\",\"age\":12},{\"id\":2,\"studentName\":\"lucy\",\"age\":15}]}";
  Teacher teacher = JSON.parseObject(complexJsonString,Teacher.class);
  

4.2 序列化

• 序列化一个Java Bean对象

User u = new User();
u.setName("王五");
u.setAge(30);
System.out.println(JSON.toJSONString(u));

// 输出结果 {"age":30,"name":"王五"}

User u1 = new User();
u1.setAge(30);
System.out.println(JSON.toJSONString(u1,SerializerFeature.WriteMapNullValue)); // 输出null，输出结果 {"age":30,"name":null}
System.out.println(JSON.toJSONString(u1,SerializerFeature.WriteNullStringAsEmpty)); // 输出""，输出结果 {"age":30,"name":""}

4.3 序列化和反序列日期

Date date = new Date();

String dateString = JSON.toJSONStringWithDateFormat(date, "yyyy-MM-dd HH:mm:ss");
System.out.println(dateString);

// 输出结果 "2018-08-03 09:44:21"

String dateString1 = "{\"time\":\"2018-08-01 22:22:22\"}";
System.out.println(JSON.parseObject(dateString1));

// 输出结果 {"time":"2018-08-01 22:22:22"}

4.4 JsonObject的一些操作

String jsonString1 = "{\"name\":\"张三\",\"age\":50}";
JSONObject jsonObject = JSON.parseObject(jsonString1);

System.out.println(jsonObject.keySet()); // 输出key集合，输出结果 [name, age]

if(jsonObject.containsKey("sex")) { // 判断key是否存在，输出结果 false
    System.out.println(true);
} else {
    System.out.println(false);
}

jsonObject.put("sex","man"); // 添加k/v键值对，输出结果 {"sex":"man","name":"张三","age":50}
System.out.println(jsonObject);

if (jsonObject.containsValue("man")) { // 判断value是否存在，输出结果 false
    System.out.println(true);
} else {
    System.out.println(false);
}

4.5 jsonArray的一些操作

String jsonArrayString1 = "[{\"id\":1,\"studentName\":\"lily\",\"age\":12},{\"id\":2,\"studentName\":\"lucy\",\"age\":15}]";
JSONArray jsonArray = JSON.parseArray(jsonArrayString1);

for (int i = 0; i < jsonArray.size(); i++) { // 遍历输出
    JSONObject jsonObj= jsonArray.getJSONObject(i);
    System.out.println(jsonObj.get("id"));
}

Student s3 = new Student(3,"学生乙",15);
jsonArray.add(s3); // 添加新jsonobject对象，输出结果 3
System.out.println(jsonArray.size());

if(jsonArray.contains(s3)) { // 判断是否存在，输出结果 true
    System.out.println(true);
} else {
    System.out.println(false);
}

5.Scala API

5.1 反序列化

• demo日志内容

  • data.log

  {"name":"张三","age":10}
  {"name":"李四","age":11}
  {"name":"李四"}
  {"age":11}
  

  • data1.log

  {"data":[{"label":"123","acc":1,"version":"4.3.1"}]}
  {"data":[{"label":"789","acc":1,"version":"4.3.1"},{"label":"78","acc":100,"version":"4.3.1"}]}
  {"data":[{"label":"5356","acc":1,"version":"4.3.1"}]}
  

• 反序列化简单json字符串

val spark = SparkSession.builder().master("local[2]").appName("FastJsonTest").getOrCreate() 
val input1 = "data.log"

val jsonRDD1 = spark.sparkContext.textFile(input1)

val dataRDD1 = jsonRDD1.map(json => {
  val jsonObject = JSON.parseObject(json)
  val name = jsonObject.getOrDefault("name",null)
  val age = jsonObject.getOrDefault("age",null)
  (name,age)
})

dataRDD1.foreach(println)

// 输出结果 
(李四,null)
(null,11)
(张三,10)
(李四,11)

• 反序列化简单json字符串组，实现一行变多行地解析json字符串。这个我也没找到很好的方法，欢迎读者指教一下
  • 方法一：字符串处理

  val input2 = "data1.log"
  val jsonRDD2 = spark.sparkContext.textFile(input2)
  
  val dataRDD2 = jsonRDD2.map(json => {
    JSON.parseObject(json).getJSONArray("data").toString
  }).map(x => x.substring(1,x.length-1).replace("},{","}---{"))  // 去掉字符串中的[]，并替换},{成}---{，目的是用于区分
    .flatMap(x => x.split("---"))  // 字符串按----拆分
    .map(x => JSON.parseObject(x))
  
  val data2 = dataRDD2.map(jsonObject => {
    val version = jsonObject.getOrDefault("version",null)
    val label = jsonObject.getOrDefault("label",null)
    val acc = jsonObject.getOrDefault("acc",null)
    (version,label,acc)
  })
  
  data2.foreach(println)
  
  // 输出结果
  (4.3.1,5356,1)
  (4.3.1,123,1)
  (4.3.1,789,1)
  (4.3.1,78,100)
  

  • 方法二：List

  val dataRDD3 = jsonRDD2.flatMap(json => {
    val jsonArray = JSON.parseObject(json).getJSONArray("data")
    var dataList : List[String] = List()  // 创建一个List
    for (i <- 0 to jsonArray.size()-1) {
      dataList = jsonArray.get(i).toString :: dataList
    }
    dataList
  }).map(x => JSON.parseObject(x))
  
  val data3 = dataRDD3.map(jsonObject => {
    val version = jsonObject.getOrDefault("version",null)
    val label = jsonObject.getOrDefault("label",null)
    val acc = jsonObject.getOrDefault("acc",null)
    (version,label,acc)
  })
  
  data3.foreach(println)
  
  // 输出结果
  (4.3.1,5356,1)
  (4.3.1,123,1)
  (4.3.1,789,1)
  (4.3.1,78,100)
  

5.2 序列化

• 序列化一个简单java Bean对象

val arr = Seq("tom:10", "bob:14", "hurry:9")
val dataRdd = spark.sparkContext.parallelize(arr)

val dataString = dataRdd.map(x => {
  val arr = x.split(":")
  val name = arr(0)
  val age = arr(1).toInt
  val u = new User(name,age)
  u
}).map(x => {
  JSON.toJSONString(x,SerializerFeature.WriteMapNullValue)  // 这里需要显示SerializerFeature中的某一个，否则会报同时匹配两个方法的错误
})

dataString.foreach(println)

// 输出结果
{"age":10,"name":"tom"}
{"age":14,"name":"bob"}
{"age":9,"name":"hurry"}

6.参考

• https://segmentfault.com/a/1190000011212806
• https://www.cnblogs.com/cdf-opensource-007/p/7106018.html
• https://github.com/alibaba/fastjson
• https://blog.csdn.net/universsky2015/article/details/77965563?locationNum=9&fps=1