主要记载Object或者Map转换为String时，去除NULL值，引用jar包为：

        <dependency>
            <groupId>com.fasterxml.jackson</groupId>
            <artifactId>jackson-parent</artifactId>
            <version>2.6.2</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-annotations</artifactId>
            <version>2.6.0</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.6.4</version>
        </dependency>

1. 转换Map为String问题

        ObjectMapper mapper = new ObjectMapper();
        //设置不写NULLmap值
        mapper.configure(SerializationFeature.WRITE_NULL_MAP_VALUES, false);
        Map testMap = new HashMap();
        testMap.put("a", null);
        testMap.put("b", 11);
        String outJson = null;
        try {
            outJson = mapper.writeValueAsString(testMap);
        } catch (JsonProcessingException e) {
            e.printStackTrace();
        }
        System.out.println(outJson);

2. 转换Object 为String问题

标记类型解释说明：

       Include.Include.ALWAYS 默认 
       Include.NON_DEFAULT 属性为默认值不序列化 
       Include.NON_EMPTY 属性为 空（""） 或者为 NULL 都不序列化 
       Include.NON_NULL 属性为NULL 不序列化 

方法一：对ObjectMapper进行属性设置

	ObjectMapper mapper = new ObjectMapper();
        mapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
        Map testMap = new HashMap();
        testMap.put("a", null);
        testMap.put("b", 11);
        User user = new User(1, null, null, testMap);
        String outJson = null;
        try {
            outJson = mapper.writeValueAsString(user);
        } catch (JsonProcessingException e) {
            e.printStackTrace();
        }
        System.out.println(outJson);

方法二：通过设置注解实现，方法上添加则只对具体属性有效，类上添加对所有属性有效

@JsonInclude(JsonInclude.Include.NON_NULL)
public class User {
    public User() {
    }