如何使用杰克逊2.6从对象生成json？

Question

我尝试使用Jackson 2.6从我创建的对象中生成一个json文件。 而且我的Android Studio中出现错误“ java.io.FileNotFoundException：/Users/kent/Desktop/sample.json：打开失败：ENOENT（无此类文件或目录）”。

我是否错过了代码中的任何内容？

我的数据如下：

school id: A1, "Point Grey"
Student name: "Kent", "Age": 43
Student name: "Jane", "Age": 18
Student name: "Winnie", "Age": 19 

school id: B1, "Prince of Wales"
Student name: "Steven", "Age": 11
Student name: "Michelle", "Age": 30
Student name: "Ronald", "Age": 20

我的目录如下：

public class DIRECTORY {
   private Map<String, SCHOOL> schools = new HashMap<String, SCHOOL>();


    public void setSchools(Map<String, SCHOOL> schoolsMap) {
    this.schools =  schoolsMap;
    }

 public Map<String, SCHOOL> getSchools() {return this.schools;}


 public void addSchool(String schoolId, String schoolName) {
     SCHOOL school = new SCHOOL();
     school.setSchoolId(schoolId);
     school.setSchoolName(schoolName);
     schools.put(schoolId,school);

   }

    public SCHOOL getSchoolById(String schoolId) {
        schools.get(schoolId);
    }

   }

我的学校课程如下：

public class SCHOOL {
private String schoolId;
private String schoolName;
private List<STUDENT> students = new ArrayList<>();

//getter and setter for schoolid and school name 
public void setStudents(STUDENT students) {
    this.students = (List<STUDENT>) students;
}
public List<STUDENT> getStudents() {return this.students;}
public void addStudent(String names, String age) {
    STUDENT student = new STUDENT();
    student.setNames(names);
    student.setAge(age);
    students.add(student);
}

我的学生班级如下：

public class STUDENT {
private String names;
private String age;
//getter and setter for name and age

}

我的数据如下：

private static DIRECTORY createDummySchool(){

    DIRECTORY directory = new DIRECTORY();
    directory.addSchool("A1", "Point Grey");
    directory.addSchool("B1", "Prince of Wales");

    SCHOOL schoolA1 = directory.getSchoolById("A1");

    schoolA1.addStudent("kent", "43");
    schoolA1.addStudent("Winnie", "19");
    schoolA1.addStudent("Jane", "18");

    SCHOOL schoolB1 = directory.getSchoolById("B1");
    schoolB1.addStudent("Steven", "11");
    schoolB1.addStudent("Michelle", "30");
    schoolB1.addStudent("Ronald", "20");

    return directory;
}

我的目录列表如下：

public String outputDirectorylist(List<DIRECTORY> directorylist) {
    StringBuilder sb = new StringBuilder();
    for (DIRECTORY directory:directorylist) {
        sb.append(school.getSchoolId());
        sb.append(",");
        sb.append(school.getSchoolName());
        sb.append(";");
    }

    return String.valueOf(sb);

}

我的主课如下：

 ....

    DIRECTORY directory = createDummySchool();
    ObjectMapper mapper = new ObjectMapper();


    try{

        mapper.writeValue(new File("/Users/kent/Desktop/sample.json"), directory);


    }catch (IOException e) {
        e.printStackTrace();}
    .....