Jackson物件序列化
這裡將介紹將Java物件序列化到一個JSON文件,然後再讀取JSON文件取得轉換為物件。在這個例子中,創建了Student類別。建立將有學生物件以JSON表示在一個student.json檔案。
建立一個名為JacksonTester在Java類別檔案在C:>Jackson_WORKSPACE.
檔案: 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:
C:\Jackson_WORKSPACE>javac JacksonTester.java
驗證輸出結果
C:\Jackson_WORKSPACE>java JacksonTester
Jackson資料綁定泛型
在簡單的資料綁定中,我們使用String作為關鍵對象,並作為一個值對象映射類別。相反,我們可以使用具體的Java物件和類型強制轉換到JSON使用。
考慮下面的範例使用一個類別的UserData來保存使用者專用資料。
建立一個名為JacksonTester在Java類別檔案目錄C:>Jackson_WORKSPACE.
檔案名稱: JacksonTester.java
Student [ name: Mahesh, age: 10 ]
驗證輸出
使用javacester.Tester
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; } }
C:\Jackson_WORKSPACE>javac JacksonTester.java