使用xStream对（Java对象、List集合、Map ）到JSON转换、从JSON转换java对象

XStream对JSON的支持

xStream对JSON也有非常好的支持，它提供了2个模型驱动。用这2个驱动可以完成Java对象到JSON的相互转换。使用JettisonMappedXmlDriver驱动，将Java对象转换成json，需要添加jettison.jar

一、准备工作

1、 下载jar包、及官方资源

xStream的jar下载地址：
https://nexus.codehaus.org/content/repositories/releases/com/thoughtworks/xstream/xstream-distribution/1.3.1/xstream-distribution-1.3.1-bin.zip
官方的示例很全，官方参考示例：http://xstream.codehaus.org/tutorial.html

添加xstream-1.3.1.jar文件到工程中，就可以开始下面的工作

1、 用JettisonMappedXmlDriver完成Java对象到JSON的转换

Java代码

/**

* <b>function:</b>XStream结合JettisonMappedXmlDriver驱动，转换Java对象到JSON

* 需要添加jettison jar

* @author hoojo

* @createDate Nov 27, 2010 1:23:18 PM

*/

@Test

public void writeEntity2JETTSON() {

failRed("=======JettisonMappedXmlDriver===JavaObject >>>> JaonString=========");

xstream = new XStream(new JettisonMappedXmlDriver());

xstream.setMode(XStream.NO_REFERENCES);

xstream.alias("student", Student.class);

fail(xstream.toXML(bean));

}

运行后结果如下：

=======JettisonMappedXmlDriver===JavaObject >>>> JaonString=========

Jaon代码

{"student":{"id":1,"name":"jack","email":"jack@email.com","address":"china","birthday":[{},"2010-11-22"]}}

JSON的转换和XML的转换用法一样，只是创建XStream需要传递一个参数，这个参数就是xml到JSON映射转换的驱动。这里会降到两个驱动，分别是JettisonMappedXmlDriver、JsonHierarchicalStreamDriver。

2、 JsonHierarchicalStreamDriver完成Java对象到JSON的转换

Java代码

/**

* <b>function:</b>用XStream结合JsonHierarchicalStreamDriver驱动

* 转换java对象为JSON字符串

* @author hoojo

* @createDate Nov 27, 2010 1:16:46 PM

*/

@Test

public void writeEntiry2JSON() {

failRed("======JsonHierarchicalStreamDriver====JavaObject >>>> JaonString=========");

xstream = new XStream(new JsonHierarchicalStreamDriver());

//xstream.setMode(XStream.NO_REFERENCES);

xstream.alias("student", Student.class);

failRed("-------Object >>>> JSON---------");

fail(xstream.toXML(bean));

//failRed("========JsonHierarchicalStreamDriver==删除根节点=========");

//删除根节点

xstream = new XStream(new JsonHierarchicalStreamDriver() {

public HierarchicalStreamWriter createWriter(Writer out) {

return new JsonWriter(out, JsonWriter.DROP_ROOT_MODE);

}

});

//xstream.setMode(XStream.NO_REFERENCES);

xstream.alias("student", Student.class);

fail(xstream.toXML(bean));

}

运行后结果如下：

======JsonHierarchicalStreamDriver====JavaObject >>>> JaonString=========

-------Object >>>> JSON---------

Json代码

{"student": {

"id": 1,

"name": "jack",

"email": "jack@email.com",

"address": "china",

"birthday": {

"birthday": "2010-11-22"

}

}}

{

"id": 1,

"name": "jack",

"email": "jack@email.com",

"address": "china",

"birthday": {

"birthday": "2010-11-22"

}

}

使用JsonHierarchicalStreamDriver转换默认会给转换后的对象添加一个根节点，但是在构建JsonHierarchicalStreamDriver驱动的时候，你可以重写createWriter方法，删掉根节点。

看上面的结果，一个是默认带根节点的JSON对象，它只是将类名作为一个属性，将对象作为该属性的一个值。而另一个没有带根属性的JSON就是通过重写createWriter方法完成的。

3、 将List集合转换成JSON字符串

Java代码

@Test

public void writeList2JSON() {

failRed("======JsonHierarchicalStreamDriver====JavaObject >>>> JaonString=========");

JsonHierarchicalStreamDriver driver = new JsonHierarchicalStreamDriver();

xstream = new XStream(driver);

//xstream = new XStream(new JettisonMappedXmlDriver());//转换错误

//xstream.setMode(XStream.NO_REFERENCES);

xstream.alias("student", Student.class);

List<Student> list = new ArrayList<Student>();

list.add(bean);//add

bean = new Student();

bean.setAddress("china");

bean.setEmail("tom@125.com");

bean.setId(2);

bean.setName("tom");

Birthday day = new Birthday("2010-11-22");

bean.setBirthday(day);

list.add(bean);//add

bean = new Student();

bean.setName("jack");

list.add(bean);//add

fail(xstream.toXML(list));

//failRed("========JsonHierarchicalStreamDriver==删除根节点=========");

//删除根节点

xstream = new XStream(new JsonHierarchicalStreamDriver() {

public HierarchicalStreamWriter createWriter(Writer out) {

return new JsonWriter(out, JsonWriter.DROP_ROOT_MODE);

}

});

xstream.alias("student", Student.class);

fail(xstream.toXML(list));

}

运行后结果如下

======JsonHierarchicalStreamDriver====JavaObject >>>> JaonString=========

Json代码

##{"list": [

{

"id": 1,

"name": "jack",

"email": "jack@email.com",

"address": "china",

"birthday": {

"birthday": "2010-11-22"

}

},

{

"id": 2,

"name": "tom",

"email": "tom@125.com",

"address": "china",

"birthday": {

"birthday": "2010-11-22"

}

},

{

"id": 0,

"name": "jack"

}

]}

#[

{

"id": 1,

"name": "jack",

"email": "jack@email.com",

"address": "china",

"birthday": {

"birthday": "2010-11-22"

}

},

{

"id": 2,

"name": "tom",

"email": "tom@125.com",

"address": "china",

"birthday": {

"birthday": "2010-11-22"

}

},

{

"id": 0,

"name": "jack"

}

]

上面的list1是使用JsonHierarchicalStreamDriver 转换的，当然你也可以使用JettisonMappedXmlDriver驱动进行转换；用JettisonMappedXmlDriver转换后，你会发现格式不同而且没有根属性。

4、 Map转换json

Java代码

@Test

public void writeMap2JSON() {

failRed("======JsonHierarchicalStreamDriver==== Map >>>> JaonString=========");

xstream = new XStream(new JsonHierarchicalStreamDriver());

//xstream = new XStream(new JettisonMappedXmlDriver());

xstream.alias("student", Student.class);

Map<String, Student> map = new HashMap<String, Student>();

map.put("No.1", bean);//put

bean = new Student();

bean.setAddress("china");

bean.setEmail("tom@125.com");

bean.setId(2);

bean.setName("tom");

bean.setBirthday(new Birthday("2010-11-21"));

map.put("No.2", bean);//put

bean = new Student();

bean.setName("jack");

map.put("No.3", bean);//put

fail(xstream.toXML(map));

//failRed("========JsonHierarchicalStreamDriver==删除根节点=========");

//删除根节点

xstream = new XStream(new JsonHierarchicalStreamDriver() {

public HierarchicalStreamWriter createWriter(Writer out) {

return new JsonWriter(out, JsonWriter.DROP_ROOT_MODE);

}

});

xstream.alias("student", Student.class);

fail(xstream.toXML(map));

}

运行后结果如下：

======JsonHierarchicalStreamDriver==== Map >>>> JaonString=========

Json代码

{"map": [

[

"No.3",

{

"id": 0,

"name": "jack"

}

],

[

"No.1",

{

"id": 1,

"name": "jack",

"email": "jack@email.com",

"address": "china",

"birthday": {

"birthday": "2010-11-22"

}

}

],

[

"No.2",

{

"id": 2,

"name": "tom",

"email": "tom@125.com",

"address": "china",

"birthday": {

"birthday": "2010-11-21"

}

}

]

]}

[

[

"No.3",

{

"id": 0,

"name": "jack"

}

],

[

"No.1",

{

"id": 1,

"name": "jack",

"email": "jack@email.com",

"address": "china",

"birthday": {

"birthday": "2010-11-22"

}

}

],

[

"No.2",

{

"id": 2,

"name": "tom",

"email": "tom@125.com",

"address": "china",

"birthday": {

"birthday": "2010-11-21"

}

}

]

]

5、 将JSON转换java对象

Java代码

/**

* <b>function:</b>JsonHierarchicalStreamDriver可以将简单的json字符串转换成java对象，list、map转换不成功；

* JsonHierarchicalStreamDriver读取JSON字符串到java对象出错

* @author hoojo

* @createDate Nov 27, 2010 1:22:26 PM

* @throws JSONException

*/

@Test

public void readJSON2Object() throws JSONException {

String json = "{\"student\": {" +

"\"id\": 1," +

"\"name\": \"haha\"," +

"\"email\": \"email\"," +

"\"address\": \"address\"," +

"\"birthday\": {" +

"\"birthday\": \"2010-11-22\"" +

"}" +

"}}";

//JsonHierarchicalStreamDriver读取JSON字符串到java对象出错，但JettisonMappedXmlDriver可以

xstream = new XStream(new JettisonMappedXmlDriver());

xstream.alias("student", Student.class);

fail(xstream.fromXML(json).toString());

//JettisonMappedXmlDriver转换List集合出错，但JsonHierarchicalStreamDriver可以转换正确

//JettisonMappedXmlDriver 转换的字符串 {"list":{"student":[{"id":1,"name":"haha","email":"email","address":"address","birthday":[{},"2010-11-22"]}]},"student":{"id":2,"name":"tom","email":"tom@125.com","address":"china","birthday":[{},"2010-11-22"]}}

json = "{\"list\": [{" +

"\"id\": 1," +

"\"name\": \"haha\"," +

"\"email\": \"email\"," +

"\"address\": \"address\"," +

"\"birthday\": {" +

"\"birthday\": \"2010-11-22\"" +

"}" +

"},{" +

"\"id\": 2," +

"\"name\": \"tom\"," +

"\"email\": \"tom@125.com\"," +

"\"address\": \"china\"," +

"\"birthday\": {" +

"\"birthday\": \"2010-11-22\"" +

"}" +

"}]}";

System.out.println(json);//用js转换成功

List list = (List) xstream.fromXML(json);

System.out.println(list.size());//0好像转换失败

}

运行后结果如下：

Json代码

haha#1#address#2010-11-22#email

{"list": [{"id": 1,"name": "haha","email": "email","address": "address","birthday": {"birthday": "2010-11-22"}},

{"id": 2,"name": "tom","email": "tom@125.com","address": "china","birthday": {"birthday": "2010-11-22"}}]}

0

JSON到Java的转换是fromXML方法