使用Jackson转换JavaBean遇到的问题
??? 今天想试一下Jackson与JavaBean之间的相互转换效果，写了个简单的例子，如下所示:
???
package com.huse.java.xmljson;import java.util.Date;import org.codehaus.jackson.map.annotate.JsonDeserialize;import org.codehaus.jackson.map.annotate.JsonSerialize; public class DateBeanTest {public String toString() {return "DateBeanTest [name=" + name + ", sqlDate="+ sqlDate.toLocaleString() + ", ctime="+ ctime.toLocaleString() + "]";}private String name;private java.sql.Date sqlDate;public String getName() {return name;}public void setName(String name) {this.name = name;}public DateBeanTest(String name, java.sql.Date sqlDate, Date ctime) {super();this.name = name;this.sqlDate = sqlDate;this.ctime = ctime;}public DateBeanTest() {super();}@JsonDeserialize(using = CustomSqlDateDeSerializer.class)public void setSqlDate(java.sql.Date sqlDate) {this.sqlDate = sqlDate;}@JsonDeserialize(using = CustomUtilDateDeSerializer.class)public void setCtime(Date ctime) {this.ctime = ctime;}private Date ctime;@JsonSerialize(using = CustomUtilDateSerializer.class)public Date getCtime() {return ctime;}@JsonSerialize(using = CustomSqlDateSerializer.class)public java.sql.Date getSqlDate() {return sqlDate;}}??? 转换器如下：
package com.huse.java.xmljson;import java.io.IOException;import java.text.SimpleDateFormat;import java.util.Date;import org.codehaus.jackson.JsonGenerator;import org.codehaus.jackson.JsonProcessingException;import org.codehaus.jackson.map.JsonSerializer;import org.codehaus.jackson.map.SerializerProvider;/** * java日期对象经过Jackson库转换成JSON日期格式化自定义类 * * @author godfox * @date 2010-5-3 */public class CustomUtilDateSerializer extends JsonSerializer<Date> {public void serialize(Date value, JsonGenerator jgen,SerializerProvider provider) throws IOException,JsonProcessingException {SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd");String formattedDate = formatter.format(value);jgen.writeString(formattedDate);}}??
package com.huse.java.xmljson;import java.io.IOException;import java.text.ParseException;import java.text.SimpleDateFormat;import java.util.Date;import org.codehaus.jackson.JsonParser;import org.codehaus.jackson.JsonProcessingException;import org.codehaus.jackson.map.DeserializationContext;import org.codehaus.jackson.map.JsonDeserializer;public class CustomUtilDateDeSerializer extends JsonDeserializer<Date> {public Date deserialize(JsonParser jsonparser,DeserializationContext deserializationcontext) throws IOException,JsonProcessingException {SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd");Date date = null;try {date = formatter.parse(jsonparser.getText());} catch (ParseException e) {date = new Date(jsonparser.getLongValue());}return date;}}?? Jackson转换JavaBean方法如下:
??
package com.huse.java.xmljson;import java.io.StringWriter;import org.codehaus.jackson.JsonEncoding;import org.codehaus.jackson.JsonFactory;import org.codehaus.jackson.JsonGenerator;import org.codehaus.jackson.map.ObjectMapper;public class JacksonHelper {private static JacksonHelper jsonUtil;private static JsonFactory jsonFactory;private static ObjectMapper objectMapper;private JacksonHelper() {}public static JacksonHelper getInstance() {if (jsonUtil == null)jsonUtil = new JacksonHelper();return jsonUtil;}public static ObjectMapper getMapper() {if (objectMapper == null) {objectMapper = new ObjectMapper();}return objectMapper;}public static JsonFactory getFactory() {if (jsonFactory == null)jsonFactory = new JsonFactory();return jsonFactory;}public void obj2jsonSysOut(Object obj) {JsonGenerator jsonGenerator = null;JsonFactory jf = null;try {objectMapper = getMapper();//StringWriter out = new StringWriter();jf = objectMapper.getJsonFactory();jsonGenerator = jf.createJsonGenerator(System.out,JsonEncoding.UTF8);objectMapper.writeValue(jsonGenerator, obj);//jsonGenerator = jf.createJsonGenerator(out);} catch (Exception e) {e.printStackTrace();} finally {try {if (jsonGenerator != null) {jsonGenerator.close();}} catch (Exception e2) {e2.printStackTrace();}}}public String obj2json(Object obj) {try {objectMapper = getMapper();return objectMapper.writeValueAsString(obj);} catch (Exception e) {e.printStackTrace();}return null;}public Object json2obj(String json, Class<?> clz) {try {objectMapper = getMapper();return objectMapper.readValue(json, clz);} catch (Exception e) {e.printStackTrace();}return null;}}?
?? 测试方法为：
?
package com.huse.java.xmljson;import java.util.Date;public class JacksonDateBeanTest {public static void main(String[] args) {DateBeanTest t1=new DateBeanTest("test", new java.sql.Date(System.currentTimeMillis()), new Date());JacksonHelper jHelper=JacksonHelper.getInstance(); jHelper.obj2jsonSysOut(t1); System.out.println();String str=jHelper.obj2json(t1);DateBeanTest t3=(DateBeanTest) jHelper.json2obj(str, DateBeanTest.class);System.out.println(t3);}}?
???? 运行结果为：
{"name":"test","sqlDate":"2013-12-26","ctime":"2013-12-26"}?????很奇怪，为什么没打印Json转换为JavaBean的结果，试着打了几个断点看下，发现程序正常运行结束，没有中途出错，开始怀疑是不是使用了静态变量设置System.out输出后没改回来，修改代码为：
???
public void obj2jsonSysOut(Object obj) {JsonGenerator jsonGenerator = null;JsonFactory jf = null;try {objectMapper = getMapper();StringWriter out = new StringWriter();jf = objectMapper.getJsonFactory();jsonGenerator = jf.createJsonGenerator(System.out,JsonEncoding.UTF8);objectMapper.writeValue(jsonGenerator, obj);jsonGenerator = jf.createJsonGenerator(out);} catch (Exception e) {e.printStackTrace();} finally {try {if (jsonGenerator != null) {jsonGenerator.close();}} catch (Exception e2) {e2.printStackTrace();}}}??? 运行结果为：
????
{"name":"test","sqlDate":"2013-12-26","ctime":"2013-12-26"}DateBeanTest [name=test, sqlDate=2013-12-26 0:00:00, ctime=2013-12-26 0:00:00]?? ps，但我obj2json设置输出为StringWrite为什么没起作用呢？
?
?
?
?