android中json解析的两个工具：Gson和Jackson的使用小demo

1.简介

json是android与服务器通信过程中常用的数据格式，例如，如下是一个json格式的字符串：

{"address":"Nanjing","name":"NUPT","students":[{"name":"stu1","id":"10000","age":20},{"name":"stu1","id":"10001","age":21},{"name":"stu1","id":"10002","age":22}]}

2.android中常用的两个json库为：Gson和Jackson，一下就看一下它们是如何将对象转化为json字符串，以及如何将json字符串转化为java对象。
定义Student类：
public class Student {  private String name;  private String id;  private int age;  public String getName() {    return name;  }  public void setName(String name) {    this.name = name;  }  public String getId() {    return id;  }  public void setId(String id) {    this.id = id;  }  public int getAge() {    return age;  }  public void setAge(int age) {    this.age = age;  }}

定义School类：

public class School {  private String name;  private String address;  List<Student> students;  public String getName() {    return name;  }  public void setName(String name) {    this.name = name;  }  public String getAddress() {    return address;  }  public void setAddress(String address) {    this.address = address;  }  public List<Student> getStudents() {    return students;  }  public void setStudents(List<Student> students) {    this.students = students;  }}

初始化一个School的java对象，待使用：

private School initSchoolData(){      School school = new School();      school.setAddress("Nanjing");      school.setName("NUPT");      List<Student> list = new ArrayList<Student>();      for(int i= 0;i<3;i++){        Student student = new Student();        student.setAge(20+i);        student.setId("1000"+i);        student.setName("stu"+1);        list.add(student);      }      school.setStudents(list);      return school;    }

3.使用Gson，进行java对象与json字符串之间的相互转换

private void testGson(){      School school = initSchoolData();      Gson gson = new Gson();      //将对象转化为json字符串      String jsonString = gson.toJson(school).toString();      //打印      System.out.println("GSON="+jsonString);      /******分割线*****/      //将字符串转化为JSON对象      School resultSchool = gson.fromJson(jsonString, School.class);      //打印      System.out.println(resultSchool.getStudents().get(0).getName());    }
可见，Gson是通过toJson和fromJson两个方法进行转换的，使用起来十分方便。

4.使用Jackson

private void testJackson(){      School school = initSchoolData();      ObjectMapper objectMapper = new ObjectMapper();      String jsonString = "";      //将对象转化为Json字符串      try {        jsonString = objectMapper.writeValueAsString(school);        System.out.println("Jackson="+jsonString);      } catch (JsonProcessingException e) {        // TODO Auto-generated catch block        e.printStackTrace();      }      //将json字符串解析成java对象      try {        School resultSchool = objectMapper.readValue(jsonString, School.class);        //打印        System.out.println(resultSchool.getStudents().get(0).getName());      } catch (JsonParseException e) {        // TODO Auto-generated catch block        e.printStackTrace();      } catch (JsonMappingException e) {        // TODO Auto-generated catch block        e.printStackTrace();      } catch (IOException e) {        // TODO Auto-generated catch block        e.printStackTrace();      }    }

使用Jackson，主要是使用writeValueAsString和readValue这两个方法。此外，Jackson的writeValue和readValue有很多种参数类型，适用于多中场合

Gson文档： http://code.google.com/p/google-gson/
Jackson： http://jackson.codehaus.org/