Jackson對(duì)象序列化
這里將介紹將Java對(duì)象序列化到一個(gè)JSON文件，然后再讀取JSON文件獲取轉(zhuǎn)換為對(duì)象。在這個(gè)例子中，創(chuàng)建了Student類。創(chuàng)建將有學(xué)生對(duì)象以JSON表示在一個(gè)student.json文件。

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

文件: 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)證輸出結(jié)果

復(fù)制代碼代碼如下:

Student [ name: Mahesh, age: 10 ]

Jackson數(shù)據(jù)綁定泛型
在簡(jiǎn)單的數(shù)據(jù)綁定中，我們使用String作為關(guān)鍵對(duì)象，并作為一個(gè)值對(duì)象映射類。相反，我們可以使用具體的Java對(duì)象和類型強(qiáng)制轉(zhuǎn)換到JSON使用。

考慮下面的例子使用一個(gè)類的UserData來(lái)保存用戶專用數(shù)據(jù)。

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

文件名: JacksonTester.java

import java.io.File;
import java.io.IOException;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
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;
import org.codehaus.jackson.type.TypeReference;

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

      Map userDataMap = new HashMap();
      UserData studentData = new UserData(); 
      int[] marks = {1,2,3};

      Student student = new Student();
      student.setAge(10);
      student.setName("Mahesh");
      // JAVA Object
      studentData.setStudent(student);
      // JAVA String
      studentData.setName("Mahesh Kumar");
      // JAVA Boolean
      studentData.setVerified(Boolean.FALSE);
      // Array
      studentData.setMarks(marks);
      TypeReference ref = new TypeReference>() { };
      userDataMap.put("studentData1", studentData);
      mapper.writeValue(new File("student.json"), userDataMap);
      //{
      //  "studentData1":
      // {
      // "student":
      // {
      //  "name":"Mahesh",
      //  "age":10
      //   },
      //   "name":"Mahesh Kumar",
      //   "verified":false,
      //   "marks":[1,2,3]
      //  }
      //}
      userDataMap = mapper.readValue(new File("student.json"), ref);

      System.out.println(userDataMap.get("studentData1").getStudent());
      System.out.println(userDataMap.get("studentData1").getName());
      System.out.println(userDataMap.get("studentData1").getVerified());
      System.out.println(Arrays.toString(userDataMap.get("studentData1").getMarks()));
   } 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+ " ]";
  } 
}

class UserData {
  private Student student;
  private String name;
  private Boolean verified;
  private int[] marks;

  public UserData(){}

  public Student getStudent() {
   return student;
  }
  public void setStudent(Student student) {
   this.student = student;
  }
  public String getName() {
   return name;
  }
  public void setName(String name) {
   this.name = name;
  }
  public Boolean getVerified() {
   return verified;
  }
  public void setVerified(Boolean verified) {
   this.verified = verified;
  }
  public int[] getMarks() {
   return marks;
  }
  public void setMarks(int[] marks) {
   this.marks = marks;
  } 
}

驗(yàn)證輸出

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

Student [ name: Mahesh, age: 10 ]
Mahesh Kumar
false
[1, 2, 3]

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