Jackson 框架，轻易转换JSON

packagecom.hoo.test;

importjava.io.IOException;

importjava.io.StringWriter;

importjava.util.ArrayList;

importjava.util.HashMap;

importjava.util.Iterator;

importjava.util.LinkedHashMap;

importjava.util.List;

importjava.util.Map;

importjava.util.Set;

importorg.codehaus.jackson.JsonEncoding;

importorg.codehaus.jackson.JsonGenerationException;

importorg.codehaus.jackson.JsonGenerator;

importorg.codehaus.jackson.JsonParseException;

importorg.codehaus.jackson.map.JsonMappingException;

importorg.codehaus.jackson.map.ObjectMapper;

importorg.codehaus.jackson.node.JsonNodeFactory;

importorg.codehaus.jackson.xml.XmlMapper;

importorg.junit.After;

importorg.junit.Before;

importorg.junit.Test;

importcom.hoo.entity.AccountBean;

/**

*<b>function:</b>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

*@authorhoojo

*@createDate2010-11-23下午04:54:53

*@fileJacksonTest.java

*@packagecom.hoo.test

*@projectSpring3

*@blog'target='_blank'>http://blog.csdn.net/IBM_hoojo[/code]
*@emailhoojo_@126.com

*@version1.0

*/

@SuppressWarnings("unchecked")

publicclassJacksonTest{

privateJsonGeneratorjsonGenerator=null;

privateObjectMapperobjectMapper=null;

privateAccountBeanbean=null;


@Before

publicvoidinit(){

bean=newAccountBean();

bean.setAddress("china-Guangzhou");

bean.setEmail("hoojo_@126.com");

bean.setId(1);

bean.setName("hoojo");


objectMapper=newObjectMapper();

try{

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

}catch(IOExceptione){

e.printStackTrace();

}

}


@After

publicvoiddestory(){

try{

if(jsonGenerator!=null){

jsonGenerator.flush();

}

if(!jsonGenerator.isClosed()){

jsonGenerator.close();

}

jsonGenerator=null;

objectMapper=null;

bean=null;

System.gc();

}catch(IOExceptione){

e.printStackTrace();

}

}

}


3、所需要的JavaEntity

packagecom.hoo.entity;


publicclassAccountBean{

privateintid;

privateStringname;

privateStringemail;

privateStringaddress;

privateBirthdaybirthday;


//getter、setter


@Override

publicStringtoString(){

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

}

}


Birthday

packagecom.hoo.entity;


publicclassBirthday{

privateStringbirthday;


publicBirthday(Stringbirthday){

super();

this.birthday=birthday;

}


//getter、setter


publicBirthday(){}


@Override

publicStringtoString(){

returnthis.birthday;

}

}


二、Java对象转换成JSON

1、JavaBean(Entity/Model)转换成JSON

/**

*<b>function:</b>将java对象转换成json字符串

*@authorhoojo

*@createDate2010-11-23下午06:01:10

*/

@Test

publicvoidwriteEntityJSON(){


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(IOExceptione){

e.printStackTrace();

}

}


运行后结果如下：

jsonGenerator

{"address":"china-Guangzhou","name":"hoojo","id":1,"birthday":null,"email":"hoojo_@126.com"}

ObjectMapper

{"address":"china-Guangzhou","name":"hoojo","id":1,"birthday":null,"email":"hoojo_@126.com"}


上面分别利用JsonGenerator的writeObject方法和ObjectMapper的writeValue方法完成对Java对象的转换，二者传递的参数及构造的方式不同；JsonGenerator的创建依赖于ObjectMapper对象。也就是说如果你要使用JsonGenerator来转换JSON，那么你必须创建一个ObjectMapper。但是你用ObjectMapper来转换JSON，则不需要JSONGenerator。

objectMapper的writeValue方法可以将一个Java对象转换成JSON。这个方法的参数一，需要提供一个输出流，转换后可以通过这个流来输出转换后的内容。或是提供一个File，将转换后的内容写入到File中。当然，这个参数也可以接收一个JSONGenerator，然后通过JSONGenerator来输出转换后的信息。第二个参数是将要被转换的Java对象。如果用三个参数的方法，那么是一个Config。这个config可以提供一些转换时的规则，过指定的Java对象的某些属性进行过滤或转换等。

2、将Map集合转换成Json字符串

/**

*<b>function:</b>将map转换成json字符串

*@authorhoojo

*@createDate2010-11-23下午06:05:26

*/

@Test

publicvoidwriteMapJSON(){

try{

Map<String,Object>map=newHashMap<String,Object>();

map.put("name",bean.getName());

map.put("account",bean);

bean=newAccountBean();

bean.setAddress("china-Beijin");

bean.setEmail("hoojo@qq.com");

map.put("account2",bean);


System.out.println("jsonGenerator");

jsonGenerator.writeObject(map);

System.out.println("");


System.out.println("objectMapper");

objectMapper.writeValue(System.out,map);

}catch(IOExceptione){

e.printStackTrace();

}

}


转换后结果如下：

jsonGenerator

{"account2":{"address":"china-Beijin","name":null,"id":0,"birthday":null,"email":"hoojo@qq.com"},"name":"hoojo",

"account":{"address":"china-Guangzhou","name":"hoojo","id":1,"birthday":null,"email":"hoojo_@126.com"}}

objectMapper

{"account2":{"address":"china-Beijin","name":null,"id":0,"birthday":null,"email":"hoojo@qq.com"},"name":"hoojo",

"account":{"address":"china-Guangzhou","name":"hoojo","id":1,"birthday":null,"email":"hoojo_@126.com"}}


3、将List集合转换成json

/**

*<b>function:</b>将list集合转换成json字符串

*@authorhoojo

*@createDate2010-11-23下午06:05:59

*/

@Test

publicvoidwriteListJSON(){

try{

List<AccountBean>list=newArrayList<AccountBean>();

list.add(bean);


bean=newAccountBean();

bean.setId(2);

bean.setAddress("address2");

bean.setEmail("email2");

bean.setName("haha2");

list.add(bean);


System.out.println("jsonGenerator");

//list转换成JSON字符串

jsonGenerator.writeObject(list);

System.out.println();

System.out.println("ObjectMapper");

//用objectMapper直接返回list转换成的JSON字符串

System.out.println("1###"+objectMapper.writeValueAsString(list));

System.out.print("2###");

//objectMapperlist转换成JSON字符串

objectMapper.writeValue(System.out,list);

}catch(IOExceptione){

e.printStackTrace();

}

}


结果如下：

jsonGenerator

[{"address":"china-Guangzhou","name":"hoojo","id":1,"birthday":null,"email":"hoojo_@126.com"},

{"address":"address2","name":"haha2","id":2,"birthday":null,"email":"email2"}]

ObjectMapper

1###[{"address":"china-Guangzhou","name":"hoojo","id":1,"birthday":null,"email":"hoojo_@126.com"},

{"address":"address2","name":"haha2","id":2,"birthday":null,"email":"email2"}]

2###[{"address":"china-Guangzhou","name":"hoojo","id":1,"birthday":null,"email":"hoojo_@126.com"},

{"address":"address2","name":"haha2","id":2,"birthday":null,"email":"email2"}]


外面就是多了个[]中括号；同样Array也可以转换，转换的JSON和上面的结果是一样的，这里就不再转换了。~.~

4、下面来看看jackson提供的一些类型，用这些类型完成json转换；如果你使用这些类型转换JSON的话，那么你即使没有JavaBean(Entity)也可以完成复杂的Java类型的JSON转换。下面用到这些类型构建一个复杂的Java对象，并完成JSON转换。

@Test

publicvoidwriteOthersJSON(){

try{

String[]arr={"a","b","c"};

System.out.println("jsonGenerator");

Stringstr="helloworldjackson!";

//byte

jsonGenerator.writeBinary(str.getBytes());

//boolean

jsonGenerator.writeBoolean(true);

//null

jsonGenerator.writeNull();

//float

jsonGenerator.writeNumber(2.2f);

//char

jsonGenerator.writeRaw("c");

//String

jsonGenerator.writeRaw(str,5,10);

//String

jsonGenerator.writeRawValue(str,5,5);

//String

jsonGenerator.writeString(str);

jsonGenerator.writeTree(JsonNodeFactory.instance.POJONode(str));

System.out.println();


//Object

jsonGenerator.writeStartObject();//{

jsonGenerator.writeObjectFieldStart("user");//user:{

jsonGenerator.writeStringField("name","jackson");//name:jackson

jsonGenerator.writeBooleanField("sex",true);//sex:true

jsonGenerator.writeNumberField("age",22);//age:22

jsonGenerator.writeEndObject();//}


jsonGenerator.writeArrayFieldStart("infos");//infos:[

jsonGenerator.writeNumber(22);//22

jsonGenerator.writeString("thisisarray");//thisisarray

jsonGenerator.writeEndArray();//]


jsonGenerator.writeEndObject();//}



AccountBeanbean=newAccountBean();

bean.setAddress("address");

bean.setEmail("email");

bean.setId(1);

bean.setName("haha");

//complexObject

jsonGenerator.writeStartObject();//{

jsonGenerator.writeObjectField("user",bean);//user:{bean}

jsonGenerator.writeObjectField("infos",arr);//infos:[array]

jsonGenerator.writeEndObject();//}


}catch(Exceptione){

e.printStackTrace();

}

}


运行后，结果如下：

jsonGenerator

"aGVsbG8gd29ybGQgamFja3NvbiE="truenull2.2cworldjacworl"helloworldjackson!""helloworldjackson!"

{"user":{"name":"jackson","sex":true,"age":22},"infos":[22,"thisisarray"]}

{"user":{"address":"address","name":"haha","id":1,"birthday":null,"email":"email"},"infos":["a","b","c"]}


怎么样？构造的json字符串和输出的结果是一致的吧。关键看懂用JSONGenerator提供的方法，完成一个Object的构建。

三、JSON转换成Java对象

1、将json字符串转换成JavaBean对象

@Test

publicvoidreadJson2Entity(){

Stringjson="{\"address\":\"address\",\"name\":\"haha\",\"id\":1,\"email\":\"email\"}";

try{

AccountBeanacc=objectMapper.readValue(json,AccountBean.class);

System.out.println(acc.getName());

System.out.println(acc);

}catch(JsonParseExceptione){

e.printStackTrace();

}catch(JsonMappingExceptione){

e.printStackTrace();

}catch(IOExceptione){

e.printStackTrace();

}

}


很简单，用到了ObjectMapper这个对象的readValue这个方法，这个方法需要提供2个参数。第一个参数就是解析的JSON字符串，第二个参数是即将将这个JSON解析吃什么Java对象，Java对象的类型。当然，还有其他相同签名方法，如果你有兴趣可以一一尝试使用方法，当然使用的方法和当前使用的方法大同小异。运行后，结果如下：

haha

haha#1#address#null#email


2、将json字符串转换成List<Map>集合

/**

*<b>function:</b>json字符串转换成list<map>

*@authorhoojo

*@createDate2010-11-23下午06:12:01

*/

@Test

publicvoidreadJson2List(){

Stringjson="[{\"address\":\"address2\",\"name\":\"haha2\",\"id\":2,\"email\":\"email2\"},"+

"{\"address\":\"address\",\"name\":\"haha\",\"id\":1,\"email\":\"email\"}]";

try{

List<LinkedHashMap<String,Object>>list=objectMapper.readValue(json,List.class);

System.out.println(list.size());

for(inti=0;i<list.size();i++){

Map<String,Object>map=list.get(i);

Set<String>set=map.keySet();

for(Iterator<String>it=set.iterator();it.hasNext();){

Stringkey=it.next();

System.out.println(key+":"+map.get(key));

}

}

}catch(JsonParseExceptione){

e.printStackTrace();

}catch(JsonMappingExceptione){

e.printStackTrace();

}catch(IOExceptione){

e.printStackTrace();

}

}


尝试过将上面的JSON转换成List，然后List中存放AccountBean，但结果失败了。但是支持Map集合。因为你转成List.class，但是不知道List存放何种类型。只好默然Map类型。因为所有的对象都可以转换成Map结合，运行后结果如下：

2

address:address2

name:haha2

id:2

email:email2

address:address

name:haha

id:1

email:email


3、Json字符串转换成Array数组，由于上面的泛型转换不能识别到集合中的对象类型。所有这里用对象数组，可以解决这个问题。只不过它不再是集合，而是一个数组。当然这个不重要，你可以用Arrays.asList将其转换成List即可。

/**

*<b>function:</b>json字符串转换成Array

*@authorhoojo

*@createDate2010-11-23下午06:14:01

*/

@Test

publicvoidreadJson2Array(){

Stringjson="[{\"address\":\"address2\",\"name\":\"haha2\",\"id\":2,\"email\":\"email2\"},"+

"{\"address\":\"address\",\"name\":\"haha\",\"id\":1,\"email\":\"email\"}]";

try{

AccountBean[]arr=objectMapper.readValue(json,AccountBean[].class);

System.out.println(arr.length);

for(inti=0;i<arr.length;i++){

System.out.println(arr[i]);

}


}catch(JsonParseExceptione){

e.printStackTrace();

}catch(JsonMappingExceptione){

e.printStackTrace();

}catch(IOExceptione){

e.printStackTrace();

}

}


运行后的结果：

2

haha2#2#address2#null#email2

haha#1#address#null#email


4、Json字符串转换成Map集合

/**

*<b>function:</b>json字符串转换Map集合

*@authorhoojo

*@createDateNov27,20103:00:06PM

*/

@Test

publicvoidreadJson2Map(){

Stringjson="{\"success\":true,\"A\":{\"address\":\"address2\",\"name\":\"haha2\",\"id\":2,\"email\":\"email2\"},"+

"\"B\":{\"address\":\"address\",\"name\":\"haha\",\"id\":1,\"email\":\"email\"}}";

try{

Map<String,Map<String,Object>>maps=objectMapper.readValue(json,Map.class);

System.out.println(maps.size());

Set<String>key=maps.keySet();

Iterator<String>iter=key.iterator();

while(iter.hasNext()){

Stringfield=iter.next();

System.out.println(field+":"+maps.get(field));

}

}catch(JsonParseExceptione){

e.printStackTrace();

}catch(JsonMappingExceptione){

e.printStackTrace();

}catch(IOExceptione){

e.printStackTrace();

}

}


运行后结果如下：

3

success:true

A:{address=address2,name=haha2,id=2,email=email2}

B:{address=address,name=haha,id=1,email=email}


四、Jackson对XML的支持

Jackson也可以完成java对象到xml的转换，转换后的结果要比json-lib更直观，不过它依赖于stax2-api.jar这个jar包。

/**

*<b>function:</b>java对象转换成xml文档

*需要额外的jar包stax2-api.jar

*@authorhoojo

*@createDate2010-11-23下午06:11:21

*/

@Test

publicvoidwriteObject2Xml(){

//stax2-api-3.0.2.jar

System.out.println("XmlMapper");

XmlMapperxml=newXmlMapper();


try{

//javaBean转换成xml

//xml.writeValue(System.out,bean);

StringWritersw=newStringWriter();

xml.writeValue(sw,bean);

System.out.println(sw.toString());

//List转换成xml

List<AccountBean>list=newArrayList<AccountBean>();

list.add(bean);

list.add(bean);

System.out.println(xml.writeValueAsString(list));


//Map转换xml文档

Map<String,AccountBean>map=newHashMap<String,AccountBean>();

map.put("A",bean);

map.put("B",bean);

System.out.println(xml.writeValueAsString(map));

}catch(JsonGenerationExceptione){

e.printStackTrace();

}catch(JsonMappingExceptione){

e.printStackTrace();

}catch(IOExceptione){

e.printStackTrace();

}

}


运行上面的方法，结果如下：

XmlMapper

<unknown><address>china-Guangzhou</address><name>hoojo</name><id>1</id><birthday/><email>hoojo_@126.com</email></unknown>

<unknown><unknown><address>china-Guangzhou</address><name>hoojo</name><id>1</id><birthday/><email>hoojo_@126.com</email></unknown>

<email><address>china-Guangzhou</address><name>hoojo</name><id>1</id><birthday/><email>hoojo_@126.com</email></email></unknown>

<unknown><A><address>china-Guangzhou</address><name>hoojo</name><id>1</id><birthday/><email>hoojo_@126.com</email></A>

<B><address>china-Guangzhou</address><name>hoojo</name><id>1</id><birthday/><email>hoojo_@126.com</email></B></unknown>


看结果，根节点都是unknown这个问题还没有解决，由于根节点没有转换出来，所有导致解析xml到Java对象，也无法完成。