JSon的相互轉化

用過一些JSON的jar包，覺得還是使用jackSon比較好用，可以String轉爲JSON對象，String轉List<Bean>,String轉Bean，List<Bean>,Bean轉String。很方便。

JACKSON的maven的配置文件

Xml代碼

<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-annotations</artifactId>
<version>2.5.0</version>
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-core</artifactId>
<version>2.5.0</version>
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.5.0</version>
</dependency>

一、JSon轉list

1.1 相關jar包

1.2 相關類

import org.codehaus.jackson.map.ObjectMapper;

import org.codehaus.jackson.type.TypeReference;

import org.codehaus.jettison.json.JSONObject;

1.3 相關代碼

//這個Json是我的項目中的JSON測試的格式。

//answerJson="{'paperId':1,'paperAnswer':[{'questionId':1,'answer':'B'},{'questionId':2,'answer':'C'},{'questionId':3,'answer':'D'}]}";

//Answer爲實體類

//String轉JSON對象

JSONObject jsonObj = new JSONObject(answerJson);

//獲取JSON對象中的paperAnswer的內容

String paperAnswerJson = jsonObj.getString("paperAnswer");

//獲取JSON對象中的paperId的內容

int paperId = jsonObj.getInt("paperId");

//此處用mapper的readValue方法將String轉爲List<Answer>

//String對象中有什麼屬性，在Answer的實體類中就得有同名的屬性和get，set方法。

List<Answer> answerList = null;

answerList = mapper.readValue(paperAnswerJson,

new TypeReference<List<Answer>>()

{

});

二 List bean 與 json 的相互轉化

public static void main(String as[])

{

ObjectMapper mapper = new ObjectMapper();

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

BookGroup bookGroup1 = new BookGroup();

BookGroup bookGroup2 = new BookGroup();

BookGroup bookGroup3 = new BookGroup();

bookGroup1.setId(1);

bookGroup2.setId(2);

bookGroup3.setId(3);

bookGroup1.setBookGroup("第一");

bookGroup2.setBookGroup("第二");

bookGroup3.setBookGroup("第三");

list.add(bookGroup1);

list.add(bookGroup2);

list.add(bookGroup3);

try

{

//list to json

System.out.println("listToJson:"+mapper.writeValueAsString(list));

//使用mapper.writeValueAsString()將List<Bean> 轉爲String

String json = mapper.writeValueAsString(list);

//json to list

List<BookGroup> list2 = mapper.readValue(json, new TypeReference<List<BookGroup>>()

{

});

System.out.println(list2.get(0).getBookGroup());

//json to bean

//bookGroup4 = mapper.readValue(beanJson,BookGroup.class);

}

catch(IOException e)

{

e.printStackTrace();

}

參考其他方式與其他的轉化對象。

網頁博客參考代碼：

Jackson可以輕鬆的將Java對象轉換成json對象和xml文檔，同樣也可以將json、xml轉換成Java對象。

前面有介紹過json-lib這個框架，在線博文：http://www.cnblogs.com/hoojo/archive/2011/04/21/2023805.html

相比json-lib框架，Jackson所依賴的jar包較少，簡單易用並且性能也要相對高些。而且Jackson社區相對比較活躍，更新速度也比較快。

一、準備工作

1、下載依賴庫jar包

Jackson的jar all下載地址：http://jackson.codehaus.org/1.7.6/jackson-all-1.7.6.jar

然後在工程中導入這個jar包即可開始工作

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

因爲下面的程序是用junit測試用例運行的，所以還得添加junit的jar包。版本是junit-4.2.8

如果你需要轉換xml，那麼還需要stax2-api.jar

2、測試類基本代碼如下

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 將java對象轉換成JSON字符串，也可以將JSON字符串轉換成java對象

* 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對象轉換成JSON

1、 JavaBean(Entity/Model)轉換成JSON

/**

* function:將java對象轉換成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可以轉換java對象，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();

}

運行後結果如下：

jsonGenerator

{"address":"china-Guangzhou","name":"hoojo","id":1,"birthday":null,"email":"[email protected]"}

ObjectMapper

{"address":"china-Guangzhou","name":"hoojo","id":1,"birthday":null,"email":"[email protected]"}

上面分別利用JsonGenerator的writeObject方法和ObjectMapper的writeValue方法完成對Java對象的轉換，二者傳遞的參數及構造的方式不同；JsonGenerator的創建依賴於ObjectMapper對象。也就是說如果你要使用JsonGenerator來轉換JSON，那麼你必須創建一個ObjectMapper。但是你用ObjectMapper來轉換JSON，則不需要JSONGenerator。

objectMapper的writeValue方法可以將一個Java對象轉換成JSON。這個方法的參數一，需要提供一個輸出流，轉換後可以通過這個流來輸出轉換後的內容。或是提供一個File，將轉換後的內容寫入到File中。當然，這個參數也可以接收一個JSONGenerator，然後通過JSONGenerator來輸出轉換後的信息。第二個參數是將要被轉換的Java對象。如果用三個參數的方法，那麼是一個Config。這個config可以提供一些轉換時的規則，過指定的Java對象的某些屬性進行過濾或轉換等。

2、將Map集合轉換成Json字符串

/**

* function:將map轉換成json字符串

* @author hoojo

* @createDate 2010-11-23 下午06:05:26

@Test

public void writeMapJSON() {

try {

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

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

map.put("account", bean);

bean = new AccountBean();

bean.setAddress("china-Beijin");

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

map.put("account2", bean);

System.out.println("jsonGenerator");

jsonGenerator.writeObject(map);

System.out.println("");

System.out.println("objectMapper");

objectMapper.writeValue(System.out, map);

} catch (IOException e) {

e.printStackTrace();

}

轉換後結果如下：

jsonGenerator

{"account2":{"address":"china-Beijin","name":null,"id":0,"birthday":null,"email":"[email protected]"},"name":"hoojo",

"account":{"address":"china-Guangzhou","name":"hoojo","id":1,"birthday":null,"email":"[email protected]"}}

objectMapper

{"account2":{"address":"china-Beijin","name":null,"id":0,"birthday":null,"email":"[email protected]"},"name":"hoojo",

"account":{"address":"china-Guangzhou","name":"hoojo","id":1,"birthday":null,"email":"[email protected]"}}

3、將List集合轉換成json

/**

* function:將list集合轉換成json字符串

* @author hoojo

* @createDate 2010-11-23 下午06:05:59

@Test

public void writeListJSON() {

try {

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

list.add(bean);

bean = new AccountBean();

bean.setId(2);

bean.setAddress("address2");

bean.setEmail("email2");

bean.setName("haha2");

list.add(bean);

System.out.println("jsonGenerator");

//list轉換成JSON字符串

jsonGenerator.writeObject(list);

System.out.println();

System.out.println("ObjectMapper");

//用objectMapper直接返回list轉換成的JSON字符串

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

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

//objectMapper list轉換成JSON字符串

objectMapper.writeValue(System.out, list);

} catch (IOException e) {

e.printStackTrace();

}

結果如下：

jsonGenerator

[{"address":"china-Guangzhou","name":"hoojo","id":1,"birthday":null,"email":"[email protected]"},

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

ObjectMapper

1###[{"address":"china-Guangzhou","name":"hoojo","id":1,"birthday":null,"email":"[email protected]"},

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

2###[{"address":"china-Guangzhou","name":"hoojo","id":1,"birthday":null,"email":"[email protected]"},

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

外面就是多了個[]中括號；同樣Array也可以轉換，轉換的JSON和上面的結果是一樣的，這裏就不再轉換了。~.~

4、下面來看看jackson提供的一些類型，用這些類型完成json轉換；如果你使用這些類型轉換JSON的話，那麼你即使沒有JavaBean(Entity)也可以完成複雜的Java類型的JSON轉換。下面用到這些類型構建一個複雜的Java對象，並完成JSON轉換。

@Test

public void writeOthersJSON() {

try {

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

System.out.println("jsonGenerator");

String str = "hello world jackson!";

//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("this is array");//this is array

jsonGenerator.writeEndArray();//]

jsonGenerator.writeEndObject();//}

AccountBean bean = new AccountBean();

bean.setAddress("address");

bean.setEmail("email");

bean.setId(1);

bean.setName("haha");

//complex Object

jsonGenerator.writeStartObject();//{

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

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

jsonGenerator.writeEndObject();//}

} catch (Exception e) {

e.printStackTrace();

}

運行後，結果如下：

jsonGenerator

"aGVsbG8gd29ybGQgamFja3NvbiE=" true null 2.2c world jac worl "hello world jackson!" "hello world jackson!"

{"user":{"name":"jackson","sex":true,"age":22},"infos":[22,"this is array"]}

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

怎麼樣？構造的json字符串和輸出的結果是一致的吧。關鍵看懂用JSONGenerator提供的方法，完成一個Object的構建。

三、JSON轉換成Java對象

1、將json字符串轉換成JavaBean對象

@Test

public void readJson2Entity() {

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

try {

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

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

System.out.println(acc);

} catch (JsonParseException e) {

e.printStackTrace();

} catch (JsonMappingException e) {

e.printStackTrace();

} catch (IOException e) {

e.printStackTrace();

}

很簡單，用到了ObjectMapper這個對象的readValue這個方法，這個方法需要提供2個參數。第一個參數就是解析的JSON字符串，第二個參數是即將將這個JSON解析喫什麼Java對象，Java對象的類型。當然，還有其他相同簽名方法，如果你有興趣可以一一嘗試使用方法，當然使用的方法和當前使用的方法大同小異。運行後，結果如下：

haha

haha#1#address#null#email

2、將json字符串轉換成List<Map>集合

/**

* function:json字符串轉換成list<map>

* @author hoojo

* @createDate 2010-11-23 下午06:12:01

@Test

public void readJson2List() {

String json = "[{\"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 (int i = 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();) {

String key = it.next();

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

}

} catch (JsonParseException e) {

e.printStackTrace();

} catch (JsonMappingException e) {

e.printStackTrace();

} catch (IOException e) {

e.printStackTrace();

}

嘗試過將上面的JSON轉換成List，然後List中存放AccountBean，但結果失敗了。但是支持Map集合。因爲你轉成List.class，但是不知道List存放何種類型。只好默然Map類型。因爲所有的對象都可以轉換成Map結合，運行後結果如下：

address:address2

name:haha2

id:2

email:email2

address:address

name:haha

id:1

email:email

3、 Json字符串轉換成Array數組，由於上面的泛型轉換不能識別到集合中的對象類型。所有這裏用對象數組，可以解決這個問題。只不過它不再是集合，而是一個數組。當然這個不重要，你可以用Arrays.asList將其轉換成List即可。

/**

* function:json字符串轉換成Array

* @author hoojo

* @createDate 2010-11-23 下午06:14:01

@Test

public void readJson2Array() {

String json = "[{\"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 (int i = 0; i < arr.length; i++) {

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

}

} catch (JsonParseException e) {

e.printStackTrace();

} catch (JsonMappingException e) {

e.printStackTrace();

} catch (IOException e) {

e.printStackTrace();

}

運行後的結果：

haha2#2#address2#null#email2

haha#1#address#null#email

4、 Json字符串轉換成Map集合

/**

* function:json字符串轉換Map集合

* @author hoojo

* @createDate Nov 27, 2010 3:00:06 PM

@Test

public void readJson2Map() {

String json = "{\"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()) {

String field = iter.next();

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

}

} catch (JsonParseException e) {

e.printStackTrace();

} catch (JsonMappingException e) {

e.printStackTrace();

} catch (IOException e) {

e.printStackTrace();

}

運行後結果如下：

success:true

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

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

四、Jackson對XML的支持

Jackson也可以完成java對象到xml的轉換，轉換後的結果要比json-lib更直觀，不過它依賴於stax2-api.jar這個jar包。

/**

* function:java對象轉換成xml文檔

* 需要額外的jar包 stax2-api.jar

* @author hoojo

* @createDate 2010-11-23 下午06:11:21

@Test

public void writeObject2Xml() {

//stax2-api-3.0.2.jar

System.out.println("XmlMapper");

XmlMapper xml = new XmlMapper();

try {

//javaBean轉換成xml

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

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