数据绑定API用于JSON转换和使用属性访问或使用注解POJO(普通Java对象)。以下是它的两个类型。
简单数据绑定 - 转换JSON，从Java Maps, Lists, Strings, Numbers, Booleans 和 null 对象。
完整数据绑定 - 转换JSON到任何JAVA类型。我们将在下一章分别绑定。
ObjectMapper读/写JSON两种类型的数据绑定。数据绑定是最方便的方式是类似XML的JAXB解析器。
简单的数据绑定
简单的数据绑定是指JSON映射到Java核心数据类型。下表列出了JSON类型和Java类型之间的关系。
让我们来看看简单的数据操作绑定。在这里，我们将映射JAVA基本类型直接JSON，反之亦然。
创建一个名为JacksonTester在Java类文件在目录 C:\>Jackson_WORKSPACE.
File: JacksonTester.java
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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+ " ]"; } } |
验证结果
使用javac编译如下类：
复制代码 代码如下:
C:\Jackson_WORKSPACE>javac JacksonTester.java
现在运行jacksonTester看到的结果：
复制代码 代码如下:
C:\Jackson_WORKSPACE>java JacksonTester
验证输出结果
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{name=Mahesh, age=10}Mahesh Kumarfalse[1, 2, 3] |
全数据绑定
完全数据绑定是指JSON映射到任何Java对象。
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//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); |
让我们来看看简单的数据操作绑定。在这里，我们将直接映射Java对象到JSON，反之亦然。
创建一个名为JacksonTester在Java类文件目录 C:\>Jackson_WORKSPACE.
File: JacksonTester.java
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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+ " ]"; } } |
验证结果
使用javac编译如下类：
复制代码 代码如下:
C:\Jackson_WORKSPACE>javac JacksonTester.java
现在运行jacksonTester看到的结果：
复制代码 代码如下:
C:\Jackson_WORKSPACE>java JacksonTester
验证输出
复制代码 代码如下:
Student [ name: Mahesh, age: 10 ]
