Jackson框架:Java对象与json、xml格式的数据之间的转换
在Java项目中將一个对象转换成一段Json格式的字符串是非常常见的，能够实现这种需求的工具包也比较多，例如Gson、JSON-lib、Jackson等等。本文主要介绍Jackson的使用，Jackson除了能实现Java对象与Json串的互转外，还能將Java对象转换为Xml格式，使用较为简单而且据说效率比较高。
对于Jackson的jar包我们可以从maven资源库中下载：http://mvnrepository.com/
所需要的jar包：
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-all-1.6.2.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
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 cn.keymobile;
import java.io.IOException;
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.junit.After;
import org.junit.Before;
import org.junit.Test;
import com.fasterxml.jackson.core.JsonEncoding;
import com.fasterxml.jackson.core.JsonGenerationException;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.node.JsonNodeFactory;
import com.fasterxml.jackson.dataformat.xml.XmlMapper;
/**
* 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
* @author zhaojd
*
*/
public class JacksonTest {
private JsonGenerator jsonGenerator = null;
private ObjectMapper objectMapper = null;
private AccountBean bean = null;
@SuppressWarnings("deprecation")
@Before
public void init() {
bean = new AccountBean();
bean.setAddress("china-Guangzhou");
bean.setEmail("[email protected]");
bean.setId(1);
bean.setName("zhaojd");
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();
}
}
/**
* 1.1 java对象转换成json
*/
@Test
public void javaBeanToJson() throws Exception {
try {
System.out.println("jsonGenerator");
/**
* writeObject()可以转换Java对象；例如：JavaBean/Map/List/Array等
*/
jsonGenerator.writeObject(bean);
System.out.println();
System.out.println("ObjectMapper");
/**
* writeValue() 和 writeObject() 是相同的功能
*/
objectMapper.writeValue(System.out, bean);
} catch (IOException e) {
e.printStackTrace();
}
}
/**
* 所谓的json格式：
* {"键":"值","键":"值","键":"值"}
* jsonGenerator
* {"address":"china-Guangzhou","name":"zhaojd","id":1,"email":"[email protected]","birthday":null}
* ObjectMapper
* {"address":"china-Guangzhou","name":"zhaojd","id":1,"email":"[email protected]","birthday":null}
*/
/**
* 1.2 将Map集合转换成json字符串
* @throws Exception
*/
@Test
public void mapToJson() throws Exception {
try {
Map map = new HashMap();
map.put("name", bean.getName());
map.put("account", bean);
bean = new AccountBean();
bean.setAddress("china-Lanzhou");
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();
}
}
/**
* jsonGenerator
* {
* "account2":{"address":"china-Lanzhou","name":null,"id":0,"email":"[email protected]","birthday":null},
* "name":"zhaojd",
* "account":{"address":"china-Guangzhou","name":"zhaojd","id":1,"email":"[email protected]","birthday":null}
* }
* objectMapper
* {
* "account2":{"address":"china-Lanzhou","name":null,"id":0,"email":"[email protected]","birthday":null},
* "name":"zhaojd","
* account":{"address":"china-Guangzhou","name":"zhaojd","id":1,"email":"[email protected]","birthday":null}
* }
*/
/**
* 1.3 将List转换成json
*/
@Test
public void listToJson() throws Exception {
try {
List list = new ArrayList();
list.add(bean);
bean = new AccountBean();
bean.setId(2);
bean.setAddress("address2");
bean.setEmail("email2");
bean.setName("name2");
list.add(bean);
System.out.println("jsonGenerator");
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("直接返回list转换成的json" + objectMapper.writeValueAsString(list));
//objectMapper list转换成JSON字符串
objectMapper.writeValue(System.out, list);
} catch (IOException e) {
e.printStackTrace();
}
}
/**
* jsonGenerator
* [
* {"address":"china-Guangzhou","name":"zhaojd","id":1,"email":"[email protected]","birthday":null},
* {"address":"address2","name":"name2","id":2,"email":"email2","birthday":null}
* ]
* ObjectMapper
* 直接返回list转换成的json[
* {"address":"china-Guangzhou","name":"zhaojd","id":1,"email":"[email protected]","birthday":null},
* {"address":"address2","name":"name2","id":2,"email":"email2","birthday":null}
* ]
* [
* {"address":"china-Guangzhou","name":"zhaojd","id":1,"email":"[email protected]","birthday":null},
* {"address":"address2","name":"name2","id":2,"email":"email2","birthday":null}
* ]
*/
/**
* 1.4 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
public void othersToJson() throws Exception {
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();
}
}
/**
* 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,"email":"email","birthday":null},"infos":["a","b","c"]}
*/
/**
* 2.1 将json字符串转换成JavaBean对象
*/
@Test
public void jsonToJavaBean() throws Exception {
String json = "{\"name\":\"zhaojd\",\"email\":\"email\",\"address\":\"address\"}";
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();
}
}
/**
* zhaojd
* 0#zhaojd#email#address#null
*/
/**
* 2.2 将json 转换成List
*/
@SuppressWarnings("unchecked")
@Test
public void jsonToList() {
String json =
"[{\"address\": \"address2\",\"name\":\"zhaojd\",\"id\":2,\"email\":\"email2\"},"
+ "{\"address\":\"address\",\"name\":\"zhaojd\",\"id\":1,\"email\":\"email\"}]";
try {
List> list = objectMapper.readValue(json, List.class);
System.out.println("list的长度:" + list.size());
for (int i = 0; i < list.size(); i++) {
Map map = list.get(i);
Set set = map.keySet();
for (Iterator 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();
}
}
/**
* list的长度：2
* address:address2
* name:zhaojd
* id:2
* email:email2
* address:address
* name:zhaojd
* id:1
* email:email
*/
/**
* 2.3 json字符串转换成Array
*/
@Test
public void jsonToArray() throws Exception {
String json =
"[{\"address\": \"address2\",\"name\":\"zhaojd2\",\"id\":2,\"email\":\"email2\"},"
+ "{\"address\":\"address\",\"name\":\"zhaojd\",\"id\":1,\"email\":\"email\"}]";
try {
AccountBean[] arr = objectMapper.readValue(json, AccountBean[].class);
System.out.println("数组的长度为：" + 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();
}
}
/**
* 数组的长度为：2
* 2#zhaojd2#email2#address2#null
* 1#zhaojd#email#address#null
*/
/**
* 2.4 json转换成Map集合
*/
@SuppressWarnings("unchecked")
@Test
public void jsonToMap() throws Exception {
String json =
"{\"success\":true,\"A\":{\"address\": \"address2\",\"name\":\"zhaojd2\",\"id\":2,\"email\":\"email2\"},"
+ "\"B\":{\"address\":\"address\",\"name\":\"zhaojd\",\"id\":1,\"email\":\"email\"}}";
try {
Map> maps = objectMapper.readValue(json, Map.class);
System.out.println("map集合的长度为：" + maps.size());
Set key = maps.keySet();
Iterator 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();
}
}
/*
* map集合的长度为：3
* success:true
* A:{address=address2, name=zhaojd2, id=2, email=email2}
* B:{address=address, name=zhaojd, id=1, email=email}
*/
/**
* 3. jackson对xml的支持
*/
@Test
public void objectToXml() throws Exception {
System.out.println("XmlMapper");
XmlMapper xml = new XmlMapper();
try {
/**
* javaBean转换成xml
*/
AccountBean account = new AccountBean();
Birthday birthday = new Birthday("1992-08");
account.setAddress("广州");
account.setBirthday(birthday);
account.setEmail("mr_zhaojd");
account.setId(1);
account.setName("zhaojd");
String xmlStr = xml.writeValueAsString(account);
System.out.println(xmlStr);
/**
* List转换成xml
*/
List list = new ArrayList();
list.add(account);
list.add(account);
System.out.println(xml.writeValueAsString(list));
/**
* Map转换xml文档
*/
Map map = new HashMap();
map.put("A", account);
map.put("B", account);
System.out.println(xml.writeValueAsString(map));
} catch (JsonGenerationException e) {
e.printStackTrace();
} catch (JsonMappingException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
/**
* XmlMapper
1
zhaojd
mr_zhaojd
广州
1992-08
1
zhaojd
mr_zhaojd
广州
1992-08
1
zhaojd
mr_zhaojd
广州
1992-08
1
zhaojd
mr_zhaojd
广州
1992-08 1
zhaojd
mr_zhaojd
广州
1992-08
*/
@Test
public void xmlToObject() {
XmlMapper xmlMapper = new XmlMapper();
String xml = "1 zhaojd mr_zhaojd 广州1992-08 参考原文出处：
http://www.cnblogs.com/hoojo/archive/2011/04/22/2024628.html
http://blog.csdn.net/Rongbo_J/article/details/47986121