一、FastJson使用范例

1.1FastJson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

1.2Maven依赖

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

1.3Scala API

1.3.1反序列化

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)

1.3.2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"}

1.4Java API

1.4.1反序列化

反序列化一个简单Json字符串

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

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);

1.4.2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":""}

1.4.3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"}

1.4.4JsonObject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);
}

1.4.5 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);
}

二、Fastjson Obejct/Map/JSON/String互转

JSONObject json = new JSONObject();
json.put("aa", "11");
json.put("bb", "22");
json.put("cc", "33");
String jsonStr = json.toString();
System.out.println(jsonStr);
// {"aa":"11","bb":"22","cc":"33"}	
	
System.out.println(JSONObject.parseObject(jsonStr).get("aa"));
// 11

String o = "{'area':{'area':'1','pagetype':'home'},'pagetype':'home'}";
System.out.println(((Map) JSONObject.parseObject(o).get("area")).get("area"));
// 1
String text = JSON.toJSONString(o);
Map<String, Object> userMap = 
		JSON.parseObject(o, new TypeReference<Map<String, Object>>() {});
System.out.println(((Map) userMap.get("area")).get("NotExsit"));
// null

System.out.println(JSON.toJSONString((Map) userMap.get("area")));
// {"area":"1","pagetype":"home"}

三、Fastjson 对象或数组转JSON

使用Fastjson 把对象或数组转JSON：

package test;  
  
import java.util.ArrayList;  
import java.util.List;  
  
import com.alibaba.fastjson.JSON;  
  
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;  
    }  
  
    @Override  
    public String toString() {  
        return "User [name=" + name + ", age=" + age + "]";  
    }  
};  
  
class UserGroup {  
    private String name;  
    private List<User> users = new ArrayList<User>();  
  
    public String getName() {  
        return name;  
    }  
  
    public void setName(String name) {  
        this.name = name;  
    }  
  
    public List<User> getUsers() {  
        return users;  
    }  
  
    public void setUsers(List<User> users) {  
        this.users = users;  
    }  
  
    @Override  
    public String toString() {  
        return "UserGroup [name=" + name + ", users=" + users + "]";  
    }  
}  
  
class FastJsonTest {  
    public static void main(String[] args) {  
        // 构建用户geust  
        User guestUser = new User();  
        guestUser.setName("guest");  
        guestUser.setAge(28);  
        // 构建用户root  
        User rootUser = new User();  
        rootUser.setName("root");  
        guestUser.setAge(35);  
        // 构建用户组对象  
        UserGroup group = new UserGroup();  
        group.setName("admin");  
        group.getUsers().add(guestUser);  
        group.getUsers().add(rootUser);  
        // 用户组对象转JSON串  
        String jsonString = JSON.toJSONString(group);  
        System.out.println("jsonString:" + jsonString);  
        // JSON串转用户组对象  
        UserGroup group2 = JSON.parseObject(jsonString, UserGroup.class);  
        System.out.println("group2:" + group2);  
  
        // 构建用户对象数组  
        User[] users = new User[2];  
        users[0] = guestUser;  
        users[1] = rootUser;  
        // 用户对象数组转JSON串  
        String jsonString2 = JSON.toJSONString(users);  
        System.out.println("jsonString2:" + jsonString2);  
        // JSON串转用户对象列表  
        List<User> users2 = JSON.parseArray(jsonString2, User.class);  
        System.out.println("users2:" + users2);  
    }  
}

输出结果：

jsonString:{"name":"admin","users":[{"age":35,"name":"guest"},{"age":0,"name":"root"}]}  
group2:UserGroup [name=admin, users=[User [name=guest, age=35], User [name=root, age=0]]]  
jsonString2:[{"age":35,"name":"guest"},{"age":0,"name":"root"}]  
users2:[User [name=guest, age=35], User [name=root, age=0]]