import java.io.IOException; 
import org.codehaus.jackson.JsonGenerationException;
import org.codehaus.jackson.JsonGenerator;
import org.codehaus.jackson.JsonProcessingException;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.JsonSerializer;
import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.map.SerializerProvider;
import org.junit.Test;
 
public class JsonTest { 
    protected static String getJson(Object obj) {
        ObjectMapper mapper = new ObjectMapper();
        // null替換為""
        mapper.getSerializerProvider().setNullValueSerializer(new JsonSerializer<Object>() {
            @Override
            public void serialize(Object arg0, JsonGenerator arg1, SerializerProvider arg2) throws IOException, JsonProcessingException {
                arg1.writeString("");
            }
        });
        String str = null;
        try {
            str = mapper.writeValueAsString(obj);
        } catch (JsonGenerationException e) {
            e.printStackTrace();
        } catch (JsonMappingException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return str;
    }
 
    @Test
    public void test() {
        System.out.println(getJson(new TestObject()));//TestObject必須是POJO對(duì)象
    } 
}
 
class TestObject {
    String name = "張三";
    String sex = null; 
    public String getName() {
        return name;
    } 
    public void setName(String name) {
        this.name = name;
    } 
    public String getSex() {
        return sex;
    } 
    public void setSex(String sex) {
        this.sex = sex;
    } 
}

  <dependency>
   <groupId>org.codehaus.jackson</groupId>
   <artifactId>jackson-mapper-asl</artifactId>
   <version>1.9.13</version>
  </dependency>