實(shí)例解析Java的Jackson庫中的數(shù)據(jù)綁定

更新時(shí)間：2016年01月13日 11:26:00 投稿：goldensun

這篇文章主要介紹了Java的Jackson庫中的數(shù)據(jù)綁定,這里分為通常的簡單數(shù)據(jù)綁定與全數(shù)據(jù)綁定兩種情況來講,需要的朋友可以參考下

數(shù)據(jù)綁定API用于JSON轉(zhuǎn)換和使用屬性訪問或使用注解POJO(普通Java對象)。以下是它的兩個(gè)類型。

簡單數(shù)據(jù)綁定 - 轉(zhuǎn)換JSON，從Java Maps, Lists, Strings, Numbers, Booleans 和 null 對象。

完整數(shù)據(jù)綁定 - 轉(zhuǎn)換JSON到任何JAVA類型。我們將在下一章分別綁定。

ObjectMapper讀/寫JSON兩種類型的數(shù)據(jù)綁定。數(shù)據(jù)綁定是最方便的方式是類似XML的JAXB解析器。

簡單的數(shù)據(jù)綁定
簡單的數(shù)據(jù)綁定是指JSON映射到Java核心數(shù)據(jù)類型。下表列出了JSON類型和Java類型之間的關(guān)系。

2016113113244100.png (629×269)

讓我們來看看簡單的數(shù)據(jù)操作綁定。在這里，我們將映射JAVA基本類型直接JSON，反之亦然。

創(chuàng)建一個(gè)名為JacksonTester在Java類文件在目錄 C:\>Jackson_WORKSPACE.

File: JacksonTester.java

import java.io.File;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

import org.codehaus.jackson.JsonGenerationException;
import org.codehaus.jackson.JsonParseException;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.ObjectMapper;

public class JacksonTester {
  public static void main(String args[]){
   JacksonTester tester = new JacksonTester();
     try {
      ObjectMapper mapper = new ObjectMapper();

      Map<String,Object> studentDataMap = new HashMap<String,Object>(); 
      int[] marks = {1,2,3};

      Student student = new Student();
      student.setAge(10);
      student.setName("Mahesh");
      // JAVA Object
      studentDataMap.put("student", student);
      // JAVA String
      studentDataMap.put("name", "Mahesh Kumar");   
      // JAVA Boolean
      studentDataMap.put("verified", Boolean.FALSE);
      // Array
      studentDataMap.put("marks", marks);

      mapper.writeValue(new File("student.json"), studentDataMap);
      //result student.json
  //{ 
      //  "student":{"name":"Mahesh","age":10},
      //  "marks":[1,2,3],
      //  "verified":false,
      //  "name":"Mahesh Kumar"
      //}
      studentDataMap = mapper.readValue(new File("student.json"), Map.class);

      System.out.println(studentDataMap.get("student"));
      System.out.println(studentDataMap.get("name"));
      System.out.println(studentDataMap.get("verified"));
      System.out.println(studentDataMap.get("marks"));
   } catch (JsonParseException e) {
     e.printStackTrace();
   } catch (JsonMappingException e) {
     e.printStackTrace();
   } catch (IOException e) {
      e.printStackTrace();
   }
  }
}

class Student {
  private String name;
  private int age;
  public Student(){}
  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;
  }
  public String toString(){
   return "Student [ name: "+name+", age: "+ age+ " ]";
  } 
}

驗(yàn)證結(jié)果

使用javac編譯如下類：

復(fù)制代碼代碼如下:

C:\Jackson_WORKSPACE>javac JacksonTester.java

現(xiàn)在運(yùn)行jacksonTester看到的結(jié)果：

復(fù)制代碼代碼如下:

C:\Jackson_WORKSPACE>java JacksonTester

驗(yàn)證輸出結(jié)果

{name=Mahesh, age=10}
Mahesh Kumar
false
[1, 2, 3]

全數(shù)據(jù)綁定
完全數(shù)據(jù)綁定是指JSON映射到任何Java對象。

//Create an ObjectMapper instance
ObjectMapper mapper = new ObjectMapper(); 
//map JSON content to Student object
Student student = mapper.readValue(new File("student.json"), Student.class);
//map Student object to JSON content
mapper.writeValue(new File("student.json"), student);

讓我們來看看簡單的數(shù)據(jù)操作綁定。在這里，我們將直接映射Java對象到JSON，反之亦然。

創(chuàng)建一個(gè)名為JacksonTester在Java類文件目錄 C:\>Jackson_WORKSPACE.

File: JacksonTester.java

import java.io.File;
import java.io.IOException;

import org.codehaus.jackson.JsonGenerationException;
import org.codehaus.jackson.JsonParseException;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.ObjectMapper;

public class JacksonTester {
  public static void main(String args[]){
   JacksonTester tester = new JacksonTester();
   try {
     Student student = new Student();
     student.setAge(10);
     student.setName("Mahesh");
     tester.writeJSON(student);

     Student student1 = tester.readJSON();
     System.out.println(student1);

   } catch (JsonParseException e) {
     e.printStackTrace();
   } catch (JsonMappingException e) {
     e.printStackTrace();
   } catch (IOException e) {
     e.printStackTrace();
   }
  }

  private void writeJSON(Student student) throws JsonGenerationException, JsonMappingException, IOException{
   ObjectMapper mapper = new ObjectMapper(); 
   mapper.writeValue(new File("student.json"), student);
  }

  private Student readJSON() throws JsonParseException, JsonMappingException, IOException{
   ObjectMapper mapper = new ObjectMapper();
   Student student = mapper.readValue(new File("student.json"), Student.class);
   return student;
  }
}

class Student {
  private String name;
  private int age;
  public Student(){}
  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;
  }
  public String toString(){
   return "Student [ name: "+name+", age: "+ age+ " ]";
  } 
}

驗(yàn)證結(jié)果

使用javac編譯如下類：

復(fù)制代碼代碼如下:

C:\Jackson_WORKSPACE>javac JacksonTester.java

現(xiàn)在運(yùn)行jacksonTester看到的結(jié)果：

復(fù)制代碼代碼如下:

C:\Jackson_WORKSPACE>java JacksonTester

驗(yàn)證輸出

復(fù)制代碼代碼如下:

Student [ name: Mahesh, age: 10 ]

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