Jackson JSON

学习地址：

http://www.journaldev.com/2324/jackson-json-processing-api-in-java-example-tutorial

package com.tothinkgames.util.json;

import java.util.List;
import java.util.Map;

import org.codehaus.jackson.map.DeserializationConfig.Feature;
import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.map.ObjectReader;
import org.codehaus.jackson.map.ObjectWriter;

/**
 * 
 * JSON工具类
 * 
 */
public class JSONUtil {
	private static ObjectMapper objectMapper = null;
	private static ObjectWriter objectWriter = null;
	/**
	 * json串中有key为A，但指定转换的mybean中未定义属性A，会抛异常。处理：mapper.configure(org.codehaus.
	 * jackson.map.DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES,
	 * false)，加上这一条，就没问题了，正常转换。
	 * 默认的json串，如果key或value类型非字符串，需要加上双引号的，但有些json包转换出来的json串却不一定会带上双引号
	 * 。使用jackson时
	 * ，如果非字符串未加双引号，也会报错。处理：mapper.configure(org.codehaus.jackson.JsonParser
	 * .Feature.ALLOW_UNQUOTED_FIELD_NAMES, true)。
	 */
	static {
		objectMapper = new ObjectMapper();
		objectMapper.configure(Feature.FAIL_ON_UNKNOWN_PROPERTIES, false);
		objectMapper.configure(org.codehaus.jackson.JsonParser.Feature.ALLOW_UNQUOTED_CONTROL_CHARS, true);
		objectWriter = objectMapper.writer();
	}

	/**
	 * 判断对象是否为合法JSON字符串
	 * 
	 * @param Object
	 *            object
	 * @return boolean
	 */
	public static boolean mayBeJSON(Object object) {
		if (object == null || !String.class.isAssignableFrom(object.getClass())) {
			return false;
		}
		String string = (String) object;
		if (string.isEmpty()) {
			return false;
		}
		char head = string.charAt(0);
		return head == '[' || head == '{';
	}

	/**
	 * 判断对象是否为合法JSON Object的字符串
	 * 
	 * @param Object
	 *            object
	 * @return boolean
	 */
	public static boolean mayBeJSONObject(Object object) {
		if (object == null || !String.class.isAssignableFrom(object.getClass())) {
			return false;
		}
		String string = (String) object;
		if (string.isEmpty()) {
			return false;
		}
		char head = string.charAt(0);
		return head == '{';
	}

	/**
	 * 判断对象是否为合法JSON Array的字符串
	 * 
	 * @param Object
	 *            object
	 * @return boolean
	 */
	public static boolean mayBeJSONArray(Object object) {
		if (object == null || !String.class.isAssignableFrom(object.getClass())) {
			return false;
		}
		String string = (String) object;
		if (string.isEmpty()) {
			return false;
		}
		char head = string.charAt(0);
		return head == '[';
	}

	/**
	 * 将JSON串转换为对象
	 * 
	 * @param String
	 *            json JSON串
	 * @param Class
	 *            <T> clazz 指定的对象类型
	 * @return T
	 * @throws Exception
	 */
	@SuppressWarnings("unchecked")
	public static <T> T toObject(String json, Class<T> clazz) throws JSONException {
		if (json == null || json.isEmpty()) {
			return null;
		}
		ObjectReader reader = objectMapper.reader(clazz);
		try {
			return (T) reader.readValue(json);
		} catch (Exception e) {
			throw new JSONException(e.getMessage(), e);
		}
	}

	/**
	 * 将JSON串转换为List
	 * 
	 * @param String
	 *            json JSON串
	 * @return List
	 * @throws Exception
	 */
	@SuppressWarnings("rawtypes")
	public static List toList(String json) throws JSONException {
		if (json == null || json.isEmpty()) {
			return null;
		}
		ObjectReader reader = objectMapper.reader(List.class);
		try {
			return reader.readValue(json);
		} catch (Exception e) {
			throw new JSONException(e.getMessage(), e);
		}
	}

	/**
	 * 将JSON串转换为Map
	 * 
	 * @param String
	 *            json JSON串
	 * @return Map
	 * @throws Exception
	 */
	@SuppressWarnings("rawtypes")
	public static Map toMap(String json) throws JSONException {
		if (json == null || json.isEmpty()) {
			return null;
		}
		ObjectReader reader = objectMapper.reader(Map.class);
		try {
			return reader.readValue(json);
		} catch (Exception e) {
			throw new JSONException(e.getMessage(), e);
		}
	}

	/**
	 * 将对象转换为JSON串
	 * 
	 * @return String
	 * @throws Exception
	 */
	public static String toJSON(Object object) throws JSONException {
		if (object == null) {
			return null;
		}
		if (String.class.isAssignableFrom(object.getClass())) {
			return (String) object;
		}
		try {
			return objectWriter.writeValueAsString(object);
		} catch (Exception e) {
			throw new JSONException(e.getMessage(), e);
		}
	}

	public static void clearAll() {
		objectMapper = null;
		objectWriter = null;
	}

}