解析Java的Jackson庫中對象的序列化與數據泛型綁定

Jackson對象序列化
這裡將介紹將Java對象序列化到一個JSON文件，然後再讀取JSON文件獲取轉換為對象。在這個例子中，創建了Student類。創建將有學生對像以JSON表示在一個student.json文件。

創建一個名為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

驗證輸出結果復制代碼代碼如下:
Student [ name: Mahesh, age: 10 ]

Jackson數據綁定泛型
在簡單的數據綁定中，我們使用String作為關鍵對象，並作為一個值對象映射類。相反，我們可以使用具體的Java對象和類型強制轉換到JSON使用。

考慮下面的例子使用一個類的UserData來保存用戶專用數據。

創建一個名為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; } }

驗證輸出

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

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