Jackson 高性能的JSON处理 ObjectMapper

      同时Jackson可以轻松的将Java对象转换成json对象和xml文档，同样也可以将json、xml转换成Java对象。功能非常的强悍！

       大家也知道，json 在如今互联网时代应用的非常广，因为大家如此的关注，所以对json的解析性能要求也是非常高的。

一、 准备工作

1、 下载依赖库jar包

Jackson的jar all下载地址：http://jackson.codehaus.org/1.7.6/jackson-all-1.7.6.jar

然后在工程中导入这个jar包即可开始工作

官方示例：http://wiki.fasterxml.com/JacksonInFiveMinutes

因为下面的程序是用junit测试用例运行的，所以还得添加junit的jar包。版本是junit-4.2.8

如果你需要转换xml，那么还需要stax2-api.jar

2、 测试类基本代码如下

public class Jackson {

    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();
        }
    }

     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 );

     }

     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 );

     }

     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 );
     }

     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 );
     }

     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());
     }

     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=true

writeMap2Json -----------
{"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=false
writeMap2Json -----------
{"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

实体类：
/*
 * @project java
 * @package
 * @file Student.java
 * @version  1.0
 * @author   廖益平
 * @time  2011-11-8 上午03:01:08
 */

public class Student {
    /*
     *
     * Class Descripton goes here.
     *
     * @class Student
     * @version  1.0
     * @author   廖益平
     * @time  2011-11-8 上午03:01:08
     */
      private int uid;
      private String uname;
      private String upwd;
      private double number;
      private boolean isstudent;
    public int getUid() {
        return uid;
    }
    public void setUid(int uid) {
        this.uid = uid;
    }
    public String getUname() {
        return uname;
    }
    public void setUname(String uname) {
        this.uname = uname;
    }
    public String getUpwd() {
        return upwd;
    }
    public void setUpwd(String upwd) {
        this.upwd = upwd;
    }
    public double getNumber() {
        return number;
    }
    public void setNumber(double number) {
        this.number = number;
    }
    public boolean isIsstudent() {
        return isstudent;
    }
    public void setIsstudent(boolean isstudent) {
        this.isstudent = isstudent;
    }
    @Override
    public String toString() {

        return "uid="+uid+",name="+uname+",upwd="+upwd+",number="+number+",isStudent="+isstudent;
    }


}