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Jackson可以輕松的將Java對象轉換成json對象和xml文檔，異樣也可以將json、xml轉換成Java對象。
相比json-lib框架，Jackson所依賴的jar包較少，復雜易用並且功能也要絕對高些。而且Jackson社區絕對比擬活潑，更新速度也比擬快。
一、預備任務
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包即可開端任務
官方示例：http://wiki.fasterxml.com/JacksonInFiveMinutes
由於上面的順序是用junit測試用例運轉的，所以還得添加junit的jar包。版本是junit-4.2.8
假如你需求轉換xml，那麼還需求stax2-api.jar
2、 測試類根本代碼如下
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;
/**
* <b>function:</b>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
* @file JacksonTest.java
* @package com.hoo.test
* @project Spring3
* @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、 所需求的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
*/
@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相反的功用
objectMapper.writeValue(System.out, bean);
} catch (IOException e) {
e.printStackTrace();
}
}
運轉後後果如下：
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]}
下面辨別應用JsonGenerator的writeObject辦法和ObjectMapper的writeValue辦法完成對Java對象的轉換，二者傳遞的參數及結構的方式不同；JsonGenerator的創立依賴於ObjectMapper對象。也就是說假如你要運用JsonGenerator來轉換JSON，那麼你必需創立一個ObjectMapper。但是你用ObjectMapper來轉換JSON，則不需求JSONGenerator。
objectMapper的writeValue辦法可以將一個Java對象轉換成JSON。這個辦法的參數一，需求提供一個輸入流，轉換後可以經過這個流來輸入轉換後的內容。或是提供一個File，將轉換後的內容寫入到File中。當然，這個參數也可以接納一個JSONGenerator，然後經過JSONGenerator來輸入轉換後的信息。第二個參數是將要被轉換的Java對象。假如用三個參數的辦法，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對象的某些屬性停止過濾或轉換等。
2、 將Map集合轉換成Json字符串
/**
* <b>function:</b>將map轉換成json字符串
* @author hoojo
*/
@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();
}
}
轉換後後果如下：
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
/**
* <b>function:</b>將list集合轉換成json字符串
* @author hoojo
*/
@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直接前往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();
}
}
後果如下：
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"}]
裡面就是多了個[]中括號；異樣Array也可以轉換，轉換的JSON和下面的後果是一樣的，這裡就不再轉換了。~.~
4、上面來看看jackson提供的一些類型，用這些類型完成json轉換；假如你運用這些類型轉換JSON的話，那麼你即便沒有JavaBean(Entity)也可以完成復雜的Java類型的JSON轉換。上面用到這些類型構建一個復雜的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();
}
}
運轉後，後果如下：
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"]}
怎樣樣？結構的json字符串和輸入的後果是分歧的吧。關鍵看懂用JSONGenerator提供的辦法，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();
}
}
很復雜，用到了ObjectMapper這個對象的readValue這個辦法，這個辦法需求提供2個參數。第一個參數就是解析的JSON字符串，第二個參數是行將將這個JSON解析吃什麼Java對象，Java對象的類型。當然，還有其他相反簽名辦法，假如你有興味可以逐個嘗試運用辦法，當然運用的辦法和以後運用的辦法迥然不同。運轉後，後果如下：
haha haha#1#address#null#email
2、 將json字符串轉換成List<Map>集合
/**
* <b>function:</b>json字符串轉換成list<map>
* @author hoojo
*/
@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();
}
}
嘗試過將下面的JSON轉換成List，然後List中寄存AccountBean，但後果失敗了。但是支持Map集合。由於你轉成List.class，但是不知道List寄存何品種型。只好默然Map類型。由於一切的對象都可以轉換成Map結合，運轉後後果如下：
2 address:address2 name:haha2 id:2 email:email2 address:address name:haha id:1 email:email
3、 Json字符串轉換成Array數組，由於下面的泛型轉換不能辨認到集合中的對象類型。一切這裡用對象數組，可以處理這個問題。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。
/**
* <b>function:</b>json字符串轉換成Array
* @author hoojo
*/
@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();
}
}
運轉後的後果：
2 haha2#2#address2#null#email2 haha#1#address#null#email
4、 Json字符串轉換成Map集合
/**
* <b>function:</b>json字符串轉換Map集合
* @author hoojo */
@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();
}
}
運轉後後果如下：
3
success:true
A:{address=address2, name=haha2, id=2, email=email2}
B:{address=address, name=haha, id=1, email=email}
四、Jackson對XML的支持
Jackson也可以完成java對象到xml的轉換，轉換後的後果要比json-lib更直觀，不過它依賴於stax2-api.jar這個jar包。
/**
* <b>function:</b>java對象轉換成xml文檔
* 需求額定的jar包 stax2-api.jar
* @author hoojo
*/
@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);
StringWriter sw = new StringWriter();
xml.writeValue(sw, bean);
System.out.println(sw.toString());
//List轉換成xml
List<AccountBean> list = new ArrayList<AccountBean>();
list.add(bean);
list.add(bean);
System.out.println(xml.writeValueAsString(list));
//Map轉換xml文檔
Map<String, AccountBean> map = new HashMap<String, AccountBean>();
map.put("A", bean);
map.put("B", bean);
System.out.println(xml.writeValueAsString(map));
} catch (JsonGenerationException e) {
e.printStackTrace();
} catch (JsonMappingException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
運轉下面的辦法，後果如下：
XmlMapper <unknown><address>china-Guangzhou</address><name>hoojo</name><id>1</id><birthday/><email>[email protected]</email></unknown> <unknown><unknown><address>china-Guangzhou</address><name>hoojo</name><id>1</id><birthday/><email>[email protected]</email></unknown> <email><address>china-Guangzhou</address><name>hoojo</name><id>1</id><birthday/><email>[email protected]</email></email></unknown> <unknown><A><address>china-Guangzhou</address><name>hoojo</name><id>1</id><birthday/><email>[email protected]</email></A> <B><address>china-Guangzhou</address><name>hoojo</name><id>1</id><birthday/><email>[email protected]</email></B></unknown>
看後果，根節點都是unknown 這個問題還沒有處理，由於根節點沒有轉換出來，一切招致解析xml到Java對象，也無法完成。
以上就是本文的全部內容，希望對大家的學習有所協助，也希望大家多多支持。
