Jackson简单小结

本文简单小结下 jackson的常用操作 ，使用的是1.9.13的版本；

1） 简单pojo转换json:

public class Employee
{
   private Integer id;
   private String firstName;
   private String lastName;

   public Employee(){

   }

   public Employee(Integer id, String firstName, String lastName, Date birthDate){
      this.id = id;
      this.firstName = firstName;
      this.lastName = lastName;
   }

   public Integer getId()
   {
      return id;
   }
   public void setId(Integer id)
   {
      this.id = id;
   }
   public String getFirstName()
   {
      return firstName;
   }
   public void setFirstName(String firstName)
   {
      this.firstName = firstName;
   }
   public String getLastName()
   {
      return lastName;
   }
   public void setLastName(String lastName)
   {
      this.lastName = lastName;
   }

   @Override
   public String toString()
   {
      return "Employee [id=" + id + ", firstName=" + firstName + ", " +
            "lastName=" + lastName + "]";
   }
}

转换：

public class JavaToJSONExample
{
   public static void main(String[] args)
   {
      @SuppressWarnings("deprecation")
      Employee employee = new Employee(1, "Lokesh", "Gupta", new Date(1981,8,18));
      ObjectMapper mapper = new ObjectMapper();
      try
      {
         mapper.writeValue(new File("c://temp/employee.json"), employee);
      } catch (JsonGenerationException e)
      {
         e.printStackTrace();
      } catch (JsonMappingException e)
      {
         e.printStackTrace();
      } catch (IOException e)
      {
         e.printStackTrace();
      }
   }
}

Output:

//In employee.json file below content will be written

{"id":1,"firstName":"Lokesh","lastName":"Gupta"}

如果要转换为良好的格式，则：

public class JavaToPrettyJSONExample
{
   public static void main(String[] args)
   {
      @SuppressWarnings("deprecation")
      Employee employee = new Employee(1, "Lokesh", "Gupta", new Date(1981,8,18));
      ObjectMapper mapper = new ObjectMapper();
      try
      {
         mapper.defaultPrettyPrintingWriter().writeValue(new File("c://temp/employee.json"), employee);
      } catch (JsonGenerationException e)
      {
         e.printStackTrace();
      } catch (JsonMappingException e)
      {
         e.printStackTrace();
      } catch (IOException e)
      {
         e.printStackTrace();
      }
   }
}

Output:

{
  "id" : 1,
  "firstName" : "Lokesh",
  "lastName" : "Gupta"
}

json转换为pojo:

public class JSONToJavaExample
{
   public static void main(String[] args)
   {
      Employee employee = null;
      ObjectMapper mapper = new ObjectMapper();
      try
      {
         employee =  mapper.readValue(new File("c://temp/employee.json"), Employee.class);
      } catch (JsonGenerationException e)
      {
         e.printStackTrace();
      } catch (JsonMappingException e)
      {
         e.printStackTrace();
      } catch (IOException e)
      {
         e.printStackTrace();
      }
      System.out.println(employee);
   }
}

Output:

Employee [id=1, firstName=Lokesh, lastName=Gupta]

2 接下来看如何把hashmap转换为json:

public class JavaToHashMapExample
{
   public static void main(String[] args)
   {
      HashMap<string, object=""> hashmap = new HashMap<string, object="">();
      hashmap.put("id", 11);
      hashmap.put("firstName", "Lokesh");
      hashmap.put("lastName", "Gupta");

      ObjectMapper mapper = new ObjectMapper();
      try
      {
         mapper.writeValue(new File("c://temp/data.json"), hashmap);
      } catch (JsonGenerationException e)
      {
         e.printStackTrace();
      } catch (JsonMappingException e)
      {
         e.printStackTrace();
      } catch (IOException e)
      {
         e.printStackTrace();
      }
   }
}

File content:

{"id":11,"lastName":"Gupta","firstName":"Lokesh"}

再把hashmap反转为json

public class HashMapToJSONExample
{
   public static void main(String[] args)
   {
      HashMap<string, object=""> hashmap = new HashMap<string, object="">();
      ObjectMapper mapper = new ObjectMapper();
      try
      {
         hashmap = mapper.readValue(new File("c://temp/data.json"), 
               new TypeReference<map<string, object="">>(){
                                                       });
      } catch (JsonGenerationException e)
      {
         e.printStackTrace();
      } catch (JsonMappingException e)
      {
         e.printStackTrace();
      } catch (IOException e)
      {
         e.printStackTrace();
      }
      System.out.println(hashmap);
   }
}

Output:

{id=11, lastName=Gupta, firstName=Lokesh}