利用Jackson对Object,Map,List,数组,枚举,日期类等化为json

    利用jackson中的objectmapper对象，转为对象为json字符串，springside对jackson的简单封装 jsonbinder ：

public class jsonbinder {	private static logger logger = loggerfactory.getlogger(jsonbinder.class);	private objectmapper mapper;	public jsonbinder(inclusion inclusion) {		mapper = new objectmapper();		//设置输出包含的属性		mapper.getserializationconfig().setserializationinclusion(inclusion);		//设置输入时忽略json字符串中存在而java对象实际没有的属性		mapper.getdeserializationconfig().set(				org.codehaus.jackson.map.deserializationconfig.feature.fail_on_unknown_properties, false);	}	/**	 * 创建输出全部属性到json字符串的binder.	 */	public static jsonbinder buildnormalbinder() {		return new jsonbinder(inclusion.always);	}	/**	 * 创建只输出非空属性到json字符串的binder.	 */	public static jsonbinder buildnonnullbinder() {		return new jsonbinder(inclusion.non_null);	}	/**	 * 创建只输出初始值被改变的属性到json字符串的binder.	 */	public static jsonbinder buildnondefaultbinder() {		return new jsonbinder(inclusion.non_default);	}	/**	 * 如果json字符串为null或"null"字符串,返回null.	 * 如果json字符串为"[]",返回空集合.	 * 	 * 如需读取集合如list/map,且不是list<string>这种简单类型时使用如下语句:	 * list<mybean> beanlist = binder.getmapper().readvalue(liststring, new typereference<list<mybean>>() {});	 */	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;		}	}	/**	 * 如果对象为null,返回"null".	 * 如果集合为空集合,返回"[]".	 */	public string tojson(object object) {		try {			return mapper.writevalueasstring(object);		} catch (ioexception e) {			logger.warn("write to json string error:" + object, e);			return null;		}	}	/**	 * 设置转换日期类型的format pattern,如果不设置默认打印timestamp毫秒数.	 */	public void setdateformat(string pattern) {		if (stringutils.isnotblank(pattern)) {			dateformat df = new simpledateformat(pattern);			mapper.getserializationconfig().setdateformat(df);			mapper.getdeserializationconfig().setdateformat(df);		}	}	/**	 * 取出mapper做进一步的设置或使用其他序列化api.	 */	public objectmapper getmapper() {		return mapper;	}}

在其他类中定义jsonbinder对象：

private static jsonbinder binder = jsonbinder.buildnondefaultbinder();

以下是对象到json字符串以及json字符串到对象的转化：

/**	 * 序列化对象/集合到json字符串.	 */	@test	public void tojson() throws exception {		//bean		testbean bean = new testbean("a");		string beanstring = binder.tojson(bean);		system.out.println("bean:" + beanstring);		assertequals("{\"name\":\"a\"}", beanstring);		//map		map<string, object> map = maps.newlinkedhashmap();		map.put("name", "a");		map.put("age", 2);		string mapstring = binder.tojson(map);		system.out.println("map:" + mapstring);		assertequals("{\"name\":\"a\",\"age\":2}", mapstring);		//list<string>		list<string> stringlist = lists.newarraylist("a", "b", "c");		string liststring = binder.tojson(stringlist);		system.out.println("string list:" + liststring);		assertequals("[\"a\",\"b\",\"c\"]", liststring);		//list<bean>		list<testbean> beanlist = lists.newarraylist(new testbean("a"), new testbean("b"));		string beanliststring = binder.tojson(beanlist);		system.out.println("bean list:" + beanliststring);		assertequals("[{\"name\":\"a\"},{\"name\":\"b\"}]", beanliststring);		//bean[]		testbean[] beanarray = new testbean[] { new testbean("a"), new testbean("b") };		string beanarraystring = binder.tojson(beanarray);		system.out.println("array list:" + beanarraystring);		assertequals("[{\"name\":\"a\"},{\"name\":\"b\"}]", beanarraystring);	}	/**	 * 从json字符串反序列化对象/集合.	 */	@test	@suppresswarnings("unchecked")	public void fromjson() throws exception {		//bean		string beanstring = "{\"name\":\"a\"}";		testbean bean = binder.fromjson(beanstring, testbean.class);		system.out.println("bean:" + bean);		//map		string mapstring = "{\"name\":\"a\",\"age\":2}";		map<string, object> map = binder.fromjson(mapstring, hashmap.class);		system.out.println("map:");		for (entry<string, object> entry : map.entryset()) {			system.out.println(entry.getkey() + " " + entry.getvalue());		}		//list<string>		string liststring = "[\"a\",\"b\",\"c\"]";		list<string> stringlist = binder.getmapper().readvalue(liststring, list.class);		system.out.println("string list:");		for (string element : stringlist) {			system.out.println(element);		}		//list<bean>		string beanliststring = "[{\"name\":\"a\"},{\"name\":\"b\"}]";		list<testbean> beanlist = binder.getmapper().readvalue(beanliststring, new typereference<list<testbean>>() {		});		system.out.println("bean list:");		for (testbean element : beanlist) {			system.out.println(element);		}	}

在我的实际项目中，遇到一个有意思的问题，我把一个对象转为为json字符串时，调用binder.tojson(bean) ，这个方法，方法总是返回null，后面发现该bean中没有默认的构造函数，加上某人构造函数就ok了。