Jackson 高性能的JSON处理 android/移动开发必备jackson-优快云博客

本文详细介绍了如何使用Jackson库进行JSON与Java对象之间的高效转换，并提供了实际示例代码，包括JSON到Java对象、Java对象到JSON、数组到JSON、列表到JSON等操作。同时展示了如何从JSON字符串转换回实体类以及从JSON到List对象的转换方法。

今天自行研究了下json ，感觉非常好用，经过测试比google的GSON快多了

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

/*
 * @project java
 * @package 
 * @file Jackson.java
 * @version  1.0
 * @author   廖益平
 * @time  2011-11-8 上午02:59:37
 */

public class Jackson {
    /*
     *
     * Class Descripton goes here.
     *
     * @class Jackson
     * @version  1.0
     * @author   廖益平
     * @time  2011-11-8 上午02:59:37
     */
    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
      * @since   2011-11-8     廖益平
      */
     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
      * @since   2011-11-8     廖益平
      */
     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
      * @since   2011-11-8     廖益平
      */
     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
      * @since   2011-11-8     廖益平
      */
     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
      * @since   2011-11-8     廖益平
      */
     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();
          }
      }

}

View Code

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;
    }
    
      
}