Jackson的JSON处理-ObjectMapper

Posted 2020-09-24

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
准备工作
1、 下载依赖库jar包
Jackson的jar all    jackson-all-1.7.6.jar
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
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:\\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:\\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:\\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:\\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:\\testjson1\\lib\\aa.txt");  
//       FileInputStream inputStream = new FileInputStream(file);  
//       Student student = mapper.readValue(inputStream,Student.class);  
//       System.out.println(student.toString()); 
         //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:\\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}}

public class Student {  
      private int uid;  
      private String uname;  
      private String upwd;  
      private double number;  
      private boolean isstudent;  
     getset方法
}