举例讲解Java的Jackson库中ObjectMapper类的使用

ObjectMapper类是Jackson库的主要类。它提供一些功能将转换成Java对象匹配JSON结构，反之亦然。它使用JsonParser和JsonGenerator的实例实现JSON实际的读/写。

类声明
以下是org.codehaus.jackson.map.ObjectMapper类的声明：

public class ObjectMapper  extends ObjectCodec   implements Versioned

嵌套类

例子
测试类基本代码如下

/*  * @project java  * @package  * @file Jackson.java  * @version 1.0  */  public class Jackson {   /*    *    * Class Descripton goes here.    *    * @class Jackson    * @version 1.0    */   public static JsonGenerator jsonGenerator = null;   private static ObjectMapper mapper = new ObjectMapper();   public static void main(String[] args) {     Student student = new Student();     student.setIsstudent(true);     student.setUid(1000);     student.setUname("xiao liao");     student.setUpwd("123");     student.setNumber(12);          Map<String, Student> stuMap = new HashMap<String, Student>();     stuMap.put("1", student);     stuMap.put("2", student);          List<Object> stuList = new ArrayList<Object>();     List<Student> stuList1 = new ArrayList<Student>();     stuList1.add(student);     student= new Student();     student.setIsstudent(false);     student.setUid(200);     student.setUname("xiao mi");     stuList1.add(student);          stuList.add(student);     stuList.add("xiao xin");     stuList.add("xiao er");     stuList.add(stuMap);          //readJson2List();     try {       //readJson2Array();       //writeArray2Json(array);       //writeJson2List();       //writeEntity2Json(student);       writeJson2Entity();       //writeMap2Json(stuMap);       //writeList2Json(stuList1);            } catch (IOException e) {       e.printStackTrace();     }   }    /**    *    * <code>writeEntity2Json</code>    * @description: TODO(实体类转换成json)    * @param object    * @throws IOException    */    public static void writeEntity2Json(Object object) throws IOException {       mapper.writeValue( new File("D://developSoft//aaadowload//testjson1//lib//aa.txt"),object );       mapper.writeValue( System.out,object );          }    /**    *    * <code>writeArray2Json</code>    * @description: TODO(数组转换成json数组)    * @param object    * @throws IOException    */    public static void writeArray2Json(Object object) throws IOException {            // writeValue具有和writeObject相同的功能      mapper.writeValue( new File("D://developSoft//aaadowload//testjson1//lib//aa.txt"),object );      mapper.writeValue(System.out,object );          }    /**    *    * <code>writeMap2Json</code>    * @description: TODO(map对象转换成json对象)    * @param object    * @throws IOException    * @since  2011-11-8   廖益平    */    public static void writeMap2Json(Object object) throws IOException {            System.out.println("使用ObjectMapper-----------");      // writeValue具有和writeObject相同的功能      System.out.println("==>"+mapper.writeValueAsString(object));      mapper.writeValue( new File("D://developSoft//aaadowload//testjson1//lib//aamap.txt"),object );      mapper.writeValue( System.out , object );    }    /**    *    * <code>writeList2Json</code>    * @description: TODO(list转换成json)    * @param object    * @throws IOException    */    public static void writeList2Json(Object object) throws IOException {      System.out.println("==>"+mapper.writeValueAsString(object));      mapper.writeValue( new File("D://developSoft//aaadowload//testjson1//lib//aamap.txt"),object );      mapper.writeValue( System.out , object );    }    /**    *    * <code>writeJson2Entity</code>    * @description: TODO(json转换成实体)    * @throws IOException    */    public static void writeJson2Entity() throws IOException {      System.out.println("json串转换成entity-------------"); //    File file = new File("D://developSoft//aaadowload//testjson1//lib//aa.txt"); //    FileInputStream inputStream = new FileInputStream(file); //    Student student = mapper.readValue(inputStream,Student.class); //    System.out.println(student.toString());      //漂亮输出      //mapper.defaultPrettyPrintingWriter().writeValueAsString(value);         String json = "{/"uid/":1000,/"uname/":/"xiao liao/",/"upwd/":/"123/",/"number/":12.0,/"isstudent/":true}";      Student student1 = mapper.readValue(json,Student.class);      System.out.println("json2:"+student1.toString());    }    /**    *    * <code>writeJson2List</code>    * @description: TODO(json专程list对象)    * @throws IOException    */    public static void writeJson2List() throws IOException {      System.out.println("json串转换成entity-------------");      File file = new File("D://developSoft//aaadowload//testjson1//lib//aa.txt");      FileInputStream inputStream = new FileInputStream(file);      Student student = mapper.readValue(inputStream,Student.class);      System.out.println(student.toString());            String json = "[{/"uid/":1000,/"uname/":/"xiao liao/",/"upwd/":/"123/",/"number/":12.0,/"isstudent/":true},{/"uid/":200,/"uname/":/"xiao mi/",/"upwd/":null,/"number/":0.0,/"isstudent/":false}]";      List<LinkedHashMap<String, Object>> s= mapper.readValue(json,List.class);      for (int i = 0; i < s.size(); i++) {        LinkedHashMap<String, Object> link = s.get(i);        Set<String> key = link.keySet();        for (Iterator iterator = key.iterator(); iterator.hasNext();) {         String string = (String) iterator.next();         System.out.println(string+"==>"+link.get(string));                }        System.out.println("json:"+i+""+s.get(i).toString());            }    }    /**     * JSON转换为List对象     */    public static void readJson2List() {     String json = "[{/"uid/":1,/"uname/":/"www/",/"number/":234,/"upwd/":/"456/"},"      + "{/"uid/":5,/"uname/":/"tom/",/"number/":3.44,/"upwd/":/"123/"}]";     try {     List<LinkedHashMap<String, Object>> list = mapper.readValue(      json, List.class);     System.out.println(list.size());     for (int i = 0; i < list.size(); i++) {      Map<String, Object> map = list.get(i);      Set<String> set = map.keySet();      for (Iterator<String> it = set.iterator(); it.hasNext();) {      String key = it.next();      System.out.println(key + ":" + map.get(key));      }     }     } catch (JsonParseException e) {     e.printStackTrace();     } catch (JsonMappingException e) {     e.printStackTrace();     } catch (IOException e) {     e.printStackTrace();     }    }    /**     * JSON转换为List对象     */    public static void readJson2Array() {      String json = "[{/"uid/":1,/"uname/":/"www/",/"number/":234,/"upwd/":/"456/"},"        + "{/"uid/":5,/"uname/":/"tom/",/"number/":3.44,/"upwd/":/"123/"}]";      try {        Student[] students = mapper.readValue(json, Student[].class);        for (Student student : students) {         System.out.println(">"+student.toString());       }      } catch (JsonParseException e) {        e.printStackTrace();      } catch (JsonMappingException e) {        e.printStackTrace();      } catch (IOException e) {        e.printStackTrace();      }    }  } 

打印结果 ：

串转换成entity-------------json2:uid=1000,name=xiao liao,upwd=123,number=12.0,isStudent=truewriteMap2Json -----------{"2":{"uid":1000,"uname":"xiao liao","upwd":"123","number":12.0,"isstudent":true},"1":{"uid":1000,"uname":"xiao liao","upwd":"123","number":12.0,"isstudent":true}}readJson2Array------------------>uid=1,name=www,upwd=456,number=234.0,isStudent=false>uid=5,name=tom,upwd=123,number=3.44,isStudent=falsewriteMap2Json -----------{"2":{"uid":1000,"uname":"xiao liao","upwd":"123","number":12.0,"isstudent":true},"1":{"uid":1000,"uname":"xiao liao","upwd":"123","number":12.0,"isstudent":true}}

大家逐个自己试试吧 ，上面也是我的测试代码