Jackson 框架，轻易转换JSON （包括时间转换）

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关于jackson中时间字符串的转换中的错误.

"yyyy-MM-dd'T'HH:mm:ss.SSSZ"
"yyyy-MM-dd'T'HH:mm:ss.SSS'Z'"
"EEE,ddMMMyyyyHH:mm:sszzz"
"yyyy-MM-dd"

当实体中存在Date类型，但是json字符串中是字符串类型

只支持以上几种格式否则报错

org.codehaus.jackson.map.JsonMappingException:Cannotconstructinstanceofjava.util.DatefromStringvalue'19802-22T12:00:00.000-0800':notavalidrepresentation(error:Cannotparsedate"19802-22T12:00:00.000-0800":notcompatiblewithanyofstandardforms("yyyy-MM-dd'T'HH:mm:ss.SSSZ","yyyy-MM-dd'T'HH:mm:ss.SSS'Z'","EEE,ddMMMyyyyHH:mm:sszzz","yyyy-MM-dd"))
at[Source:java.io.StringReader@183f74d;line:1,column:15](throughreferencechain:com.masque.json.Person["birthday"])
atorg.codehaus.jackson.map.JsonMappingException.from(JsonMappingException.java:163)
atorg.codehaus.jackson.map.deser.StdDeserializationContext.weirdStringException(StdDeserializationContext.java:220)
atorg.codehaus.jackson.map.deser.StdDeserializer._parseDate(StdDeserializer.java:511)
atorg.codehaus.jackson.map.deser.DateDeserializer.deserialize(DateDeserializer.java:26)
atorg.codehaus.jackson.map.deser.DateDeserializer.deserialize(DateDeserializer.java:17)
atorg.codehaus.jackson.map.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:230)
atorg.codehaus.jackson.map.deser.SettableBeanProperty$MethodProperty.deserializeAndSet(SettableBeanProperty.java:334)
atorg.codehaus.jackson.map.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:495)
atorg.codehaus.jackson.map.deser.BeanDeserializer.deserialize(BeanDeserializer.java:351)
atorg.codehaus.jackson.map.ObjectMapper._readMapAndClose(ObjectMapper.java:2130)
atorg.codehaus.jackson.map.ObjectMapper.readValue(ObjectMapper.java:1394)
atcom.masque.json.JacksonTo.main(JacksonTo.java:15)

查了下资料

Letter	Date or Time Component	Presentation	Examples
G	Era designator	Text	AD
y	Year	Year	1996;96
M	Month in year	Month	July;Jul;07
w	Week in year	Number	27
W	Week in month	Number	2
D	Day in year	Number	189
d	Day in month	Number	10
F	Day of week in month	Number	2
E	Day in week	Text	Tuesday;Tue
a	Am/pm marker	Text	PM
H	Hour in day (0-23)	Number	0
k	Hour in day (1-24)	Number	24
K	Hour in am/pm (0-11)	Number	0
h	Hour in am/pm (1-12)	Number	12
m	Minute in hour	Number	30
s	Second in minute	Number	55
S	Millisecond	Number	978
z	Time zone	General time zone	Pacific Standard Time;PST;GMT-08:00
Z	Time zone	RFC 822 time zone	-0800

标准时间格式

Date and Time Pattern	Result
"yyyy.MM.dd G 'at' HH:mm:ss z"	2001.07.04 AD at 12:08:56 PDT
"EEE, MMM d, ''yy"	Wed, Jul 4, '01
"h:mm a"	12:08 PM
"hh 'o''clock' a, zzzz"	12 o'clock PM, Pacific Daylight Time
"K:mm a, z"	0:08 PM, PDT
"yyyyy.MMMMM.dd GGG hh:mm aaa"	02001.July.04 AD 12:08 PM
"EEE, d MMM yyyy HH:mm:ss Z"	Wed, 4 Jul 2001 12:08:56 -0700
"yyMMddHHmmssZ"	010704120856-0700
"yyyy-MM-dd'T'HH:mm:ss.SSSZ"	2001-07-04T12:08:56.235-0700
"yyyy-MM-dd'T'HH:mm:ss.SSSXXX"	2001-07-04T12:08:56.235-07:00
"YYYY-'W'ww-u"	2001-W27-3

Jackson可以轻松的将Java对象转换成json对象和xml文档，同样也可以将json、xml转换成Java对象。

前面有介绍过json-lib这个框架，在线博文：http://www.cnblogs.com/hoojo/archive/2011/04/21/2023805.html

相比json-lib框架，Jackson所依赖的jar包较少，简单易用并且性能也要相对高些。而且Jackson社区相对比较活跃，更新速度也比较快。

一、准备工作

1、 下载依赖库jar包

Jackson的jar all下载地址：http://jackson.codehaus.org/1.7.6/jackson-all-1.7.6.jar

然后在工程中导入这个jar包即可开始工作

官方示例：http://wiki.fasterxml.com/JacksonInFiveMinutes

因为下面的程序是用junit测试用例运行的，所以还得添加junit的jar包。版本是junit-4.2.8

如果你需要转换xml，那么还需要stax2-api.jar

2、 测试类基本代码如下

package com.hoo.test;

import java.io.IOException;

import java.io.StringWriter;

import java.util.ArrayList;

import java.util.HashMap;

import java.util.Iterator;

import java.util.LinkedHashMap;

import java.util.List;

import java.util.Map;

import java.util.Set;

import org.codehaus.jackson.JsonEncoding;

import org.codehaus.jackson.JsonGenerationException;

import org.codehaus.jackson.JsonGenerator;

import org.codehaus.jackson.JsonParseException;

import org.codehaus.jackson.map.JsonMappingException;

import org.codehaus.jackson.map.ObjectMapper;

import org.codehaus.jackson.node.JsonNodeFactory;

import org.codehaus.jackson.xml.XmlMapper;

import org.junit.After;

import org.junit.Before;

import org.junit.Test;

import com.hoo.entity.AccountBean;

/**

 * function:Jackson 将java对象转换成JSON字符串，也可以将JSON字符串转换成java对象

 * jar-lib-version: jackson-all-1.6.2

 * jettison-1.0.1

 * @author hoojo

 * @createDate 2010-11-23 下午04:54:53

 * @file JacksonTest.java

 * @package com.hoo.test

 * @project Spring3

 * @blog http://blog.csdn.net/IBM_hoojo

 * @email [email protected]

 * @version 1.0

 */

@SuppressWarnings("unchecked")

public class JacksonTest {

    private JsonGenerator jsonGenerator = null;

    private ObjectMapper objectMapper = null;

    private AccountBean bean = null;

    @Before

    public void init() {

        bean = new AccountBean();

        bean.setAddress("china-Guangzhou");

        bean.setEmail("[email protected]");

        bean.setId(1);

        bean.setName("hoojo");

        objectMapper = new ObjectMapper();

        try {

            jsonGenerator = objectMapper.getJsonFactory().createJsonGenerator(System.out, JsonEncoding.UTF8);

        } catch (IOException e) {

            e.printStackTrace();

        }

    }

    @After

    public void destory() {

        try {

            if (jsonGenerator != null) {

                jsonGenerator.flush();

            }

            if (!jsonGenerator.isClosed()) {

                jsonGenerator.close();

            }

            jsonGenerator = null;

            objectMapper = null;

            bean = null;

            System.gc();

        } catch (IOException e) {

            e.printStackTrace();

        }

    }

}

3、 所需要的JavaEntity

package com.hoo.entity;

public class AccountBean {

    private int id;

    private String name;

    private String email;

    private String address;

    private Birthday birthday;

    //getter、setter

    @Override

    public String toString() {

        return this.name + "#" + this.id + "#" + this.address + "#" + this.birthday + "#" + this.email;

    }

}

Birthday

package com.hoo.entity;

public class Birthday {

    private String birthday;

    public Birthday(String birthday) {

        super();

        this.birthday = birthday;

    }

    //getter、setter

    public Birthday() {}

    @Override

    public String toString() {

        return this.birthday;

    }

}

二、Java对象转换成JSON

1、 JavaBean(Entity/Model)转换成JSON

/**

 * function:将java对象转换成json字符串

 * @author hoojo

 * @createDate 2010-11-23 下午06:01:10

 */

@Test

public void writeEntityJSON() {

    try {

        System.out.println("jsonGenerator");

        //writeObject可以转换java对象，eg:JavaBean/Map/List/Array等

        jsonGenerator.writeObject(bean);    

        System.out.println();

        System.out.println("ObjectMapper");

        //writeValue具有和writeObject相同的功能

        objectMapper.writeValue(System.out, bean);

    } catch (IOException e) {

        e.printStackTrace();

    }

}

运行后结果如下：

jsonGenerator