實例解析Java的Jackson庫中的數據綁定

數據綁定API用於JSON轉換和使用屬性訪問或使用註解POJO(普通Java對象)。以下是它的兩個類型。

簡單數據綁定- 轉換JSON，從Java Maps, Lists, Strings, Numbers, Booleans 和null 對象。

完整數據綁定- 轉換JSON到任何JAVA類型。我們將在下一章分別綁定。

ObjectMapper讀/寫JSON兩種類型的數據綁定。數據綁定是最方便的方式是類似XML的JAXB解析器。

簡單的數據綁定
簡單的數據綁定是指JSON映射到Java核心數據類型。下表列出了JSON類型和Java類型之間的關係。

讓我們來看看簡單的數據操作綁定。在這裡，我們將映射JAVA基本類型直接JSON，反之亦然。

創建一個名為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+ " ]"; } }

驗證結果

使用javac編譯如下類：
複製代碼代碼如下:
C:/Jackson_WORKSPACE>javac JacksonTester.java

現在運行jacksonTester看到的結果：
複製代碼代碼如下:
C:/Jackson_WORKSPACE>java JacksonTester

驗證輸出結果

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

全數據綁定
完全數據綁定是指JSON映射到任何Java對象。

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

讓我們來看看簡單的數據操作綁定。在這裡，我們將直接映射Java對像到JSON，反之亦然。

創建一個名為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+ " ]"; } }

驗證結果

使用javac編譯如下類：
複製代碼代碼如下:
C:/Jackson_WORKSPACE>javac JacksonTester.java

現在運行jacksonTester看到的結果：
複製代碼代碼如下:
C:/Jackson_WORKSPACE>java JacksonTester

驗證輸出複制代碼代碼如下:
Student [ name: Mahesh, age: 10 ]