Jackson simple encapsulation

 

import java.io.IOException;
import org.apache.commons.lang.StringUtils;
import org.codehaus.jackson.JsonProcessingException;
import org.codehaus.jackson.map.DeserializationConfig;
import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.map.SerializationConfig;
import org.codehaus.jackson.map.annotate.JsonSerialize.Inclusion;
import org.codehaus.jackson.map.util.JSONPObject;
import org.codehaus.jackson.type.JavaType;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Simply encapsulate Jackson and implement Mapper of JSON String<->Java Object.
 *
 * Encapsulate different output styles, use different builder functions to create instances.
 */
public class JsonMapper {

    private static Logger logger = LoggerFactory.getLogger(JsonMapper.class);
    private ObjectMapper mapper;

    public JsonMapper(Inclusion inclusion) {
        mapper = new ObjectMapper();
        //Set the style of including attributes when outputting
        mapper.setSerializationInclusion(inclusion);
        // When setting the input, ignore properties that exist in the JSON string but the Java object doesn't actually have
        mapper.configure(DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES, false);
        //It is forbidden to use int to represent the order() of Enum to deserialize Enum, it is very dangerous
        mapper.configure(DeserializationConfig.Feature.FAIL_ON_NUMBERS_FOR_ENUMS, true);
    }

    /**
     * Create a Mapper that outputs all attributes to a Json string.
     */
    public static JsonMapper buildNormalMapper() {
        return new JsonMapper(Inclusion.ALWAYS);
    }

    /**
     * Create a Mapper that only outputs non-null properties to Json strings.
     */
    public static JsonMapper buildNonNullMapper() {
        return new JsonMapper(Inclusion.NON_NULL);
    }

    /**
     * Create a Mapper that only outputs properties whose initial value has been changed to a Json string.
     */
    public static JsonMapper buildNonDefaultMapper() {
        return new JsonMapper(Inclusion.NON_DEFAULT);
    }

    /**
     * Create a Mapper that only outputs non-Null and non-Empty (such as List.isEmpty) properties to Json strings.
     */
    public static JsonMapper buildNonEmptyMapper() {
        return new JsonMapper(Inclusion.NON_EMPTY);
    }

    /**
     * If the object is Null, return "null". If the collection is empty, return "[]".
     */
    public String toJson(Object object) {

        try {
            return mapper.writeValueAsString(object);
        } catch (IOException e) {
            logger.warn("write to json string error:" + object, e);
            return null;
        }
    }

    /**
     * If the JSON string is Null or "null" string, return Null. If the JSON string is "[]", return an empty collection.
     *
     * When you need to read a collection such as List/Map, and it is not a simple type such as List<String>, first use the function constructParametricType to construct the type.
     *
     * @see #constructParametricType(Class, Class...)
     */
    public <T> T fromJson(String jsonString, Class<T> clazz) {
        if (StringUtils.isEmpty(jsonString)) {
            return null;
        }

        try {
            return mapper.readValue(jsonString, clazz);
        } catch (IOException e) {
            logger.warn("parse json string error:" + jsonString, e);
            return null;
        }
    }

    /**
     * If the JSON string is Null or "null" string, return Null. If the JSON string is "[]", return an empty collection.
     *
     * When you need to read a collection such as List/Map, and it is not a simple type such as List<String>, first use the function constructParametricType to construct the type.
     *
     * @see #constructParametricType(Class, Class...)
     */
    public <T> T fromJson(String jsonString, JavaType javaType) {
        if (StringUtils.isEmpty(jsonString)) {
            return null;
        }

        try {
            return (T) mapper.readValue(jsonString, javaType);
        } catch (IOException e) {
            logger.warn("parse json string error:" + jsonString, e);
            return null;
        }
    }

    /**
     * Construct a generic Type such as List<MyBean>,
     * Then call constructParametricType(ArrayList.class,MyBean.class)
     * Map<String,MyBean>则调用(HashMap.class,String.class, MyBean.class)
     */
    public JavaType constructParametricType(Class<?> parametrized, Class<?>... parameterClasses) {
        return mapper.getTypeFactory().constructParametricType(parametrized, parameterClasses);
    }

    /**
     * When JSON contains only some properties of Bean, update an existing Bean and only overwrite the properties of this part.
     */
    public <T> T update(T object, String jsonString) {
        try {
            return (T) mapper.readerForUpdating(object).readValue(jsonString);
        } catch (JsonProcessingException e) {
            logger.warn("update json string:" + jsonString + " to object:" + object + " error.", e);
        } catch (IOException e) {
            logger.warn("update json string:" + jsonString + " to object:" + object + " error.", e);
        }
        return null;
    }

    /**
     * Output JSONP format data.
     */
    public String toJsonP(String functionName, Object object) {
        return toJson(new JSONPObject(functionName, object));
    }

    /**
     * Set whether to use Enum's toString function to read and write Enum, when it is False, use Enum's name() function to read and write Enum, the default is False.
     * Note that this function must be called after the Mapper is created and before all read and write operations.
     */
    public void setEnumUseToString(boolean value) {
        mapper.configure(SerializationConfig.Feature.WRITE_ENUMS_USING_TO_STRING, value);
        mapper.configure(DeserializationConfig.Feature.READ_ENUMS_USING_TO_STRING, value);
    }

    /**
     * Take out the Mapper for further settings or use other serialization APIs.
     */
    public ObjectMapper getMapper() {
        return mapper;
    }
}