Jackson传输map中含有float数据的一个小坑

Jackson作为一个json的处理库，在处理数组，list，map方面非常便利。但是在进行map解析过程中，遇到一个小坑，下面进行记录。
假设我们定义一个value是object的map,并向其中传入一个Long型和Float的数据.

         ObjectMapper mapper = new ObjectMapper();  
         Map<String, Object> map = new HashMap<String, Object>();  
         map.put("sessionID", 1L);
         map.put("temperatureValue", 60.15F);

然后我们将map数据取出

      Long sessionID = ((Long) map.get("sessionID"));
      System.out.println("sessionID is " + sessionID);
      float temperatureValue = ((Float) map.get("temperatureValue"));
      System.out.println("temperatureValue is " + temperatureValue);

结果没有任何问题：

      sessionID is 1
      temperatureValue is 60.15

然后我们将此map数据进行Jaskson封装成字符串，然后进行恢复成map，再进行map数据的提取

        ObjectMapper mapper = new ObjectMapper();
        Map<String, Object> map = new HashMap<String, Object>();
        map.put("sessionID", 1L);
        map.put("temperatureValue", 60.15F);
        String jsonfromMap = mapper.writeValueAsString(map);
        System.out.println(jsonfromMap);

        Map map2 = mapper.readValue(jsonfromMap, Map.class);

        Long sessionID = ((Long) map.get("sessionID"));
        System.out.println("sessionID is " + sessionID);

        Float temperatureValue = (Float) map2.get("temperatureValue");

        System.out.println("temperatureValue-->" + temperatureValue);

结果

{"sessionID":1,"temperatureValue":60.15}
sessionID is 1

可以发现Float类型的temperatureValue 值没有解析出来。将Float改成Double，再进行解析

Double temperatureValue = (Double) map2.get("temperatureValue");

结果出来

temperatureValue-->60.15

然后再将Double转成Float。

float temperatureValue4float=(float)temperatureValue.doubleValue() ;

另附上float和double互相换砖的问题( 参考别人博客)：

double d = 3.14;  
float f = (float)d;  
System.out.println(f);  
输出结果是:3.14;   
  
float f = 127.1f;  
double d = f;  
System.out.println(d);  
输出结果是：127.0999984741211   

可以先转成BigDecimal ，再转成double

 f = 127.1f;  
        BigDecimal b = new BigDecimal(String.valueOf(f));  
         d = b.doubleValue();  
        System.out.println(d);  

以及jackson传list，map和array的方式 ,(转自http://blog.csdn.net/lansetiankong12/article/details/52584104)

package com.jingshou.jackson;  
  
import java.io.IOException;  
import java.util.ArrayList;  
import java.util.Arrays;  
import java.util.Date;  
import java.util.HashMap;  
import java.util.List;  
import java.util.Map;  
  
import com.fasterxml.jackson.databind.ObjectMapper;  
import com.jingshou.pojo.Student;  
  
public class JacksonTest2 {  
  
    public static void main(String[] args) throws IOException {  
        Student student1 = new Student();    
        student1.setId(5237);  
        student1.setName("jingshou");  
        student1.setBirthDay(new Date());  
          
        Student student3 = new Student();    
        student3.setId(5117);    
        student3.setName("saiya");    
        student3.setBirthDay(new Date());    
          
        ObjectMapper mapper = new ObjectMapper();  
            
        //Convert between List and JSON  
        List<Student> stuList = new ArrayList<Student>();  
        stuList.add(student1);  
        stuList.add(student3);  
        String jsonfromList = mapper.writeValueAsString(stuList);  
        System.out.println(jsonfromList);  
          
        //List Type is not required here.  
        List stuList2 = mapper.readValue(jsonfromList, List.class);  
        System.out.println(stuList2);      
        System.out.println("************************************");  
          
        //Convert Map to JSON  
        Map<String, Object> map = new HashMap<String, Object>();  
        map.put("studentList", stuList);  
        map.put("class", "ClassName");  
        String jsonfromMap =  mapper.writeValueAsString(map);  
        System.out.println(jsonfromMap);  
          
        Map map2 =  mapper.readValue(jsonfromMap, Map.class);  
        System.out.println(map2);  
        System.out.println(map2.get("studentList"));      
        System.out.println("************************************");     
          
        //Convert Array to JSON  
        Student[] stuArr = {student1, student3};  
        String jsonfromArr =  mapper.writeValueAsString(stuArr);  
        System.out.println(jsonfromArr);   
        Student[] stuArr2 =  mapper.readValue(jsonfromArr, Student[].class);  
        System.out.println(Arrays.toString(stuArr2));  
    }  
  
}