Jackson 框架,轻易转换JSON
2014-01-07 10:32
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Jackson可以轻松的将Java对象转换成json对象和xml文档,同样也可以将json、xml转换成Java对象。
前面有介绍过json-lib和org.json,fastjson框架 比较性能:http://www.cnblogs.com/windlaughing/p/3241776.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的jar all下载地址:http://jackson.codehaus.org/1.7.6/jackson-all-1.7.6.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
因为下面的程序是用junit测试用例运行的,所以还得添加junit的jar包。版本是junit-4.2.8
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
前面有介绍过json-lib和org.json,fastjson框架 比较性能:http://www.cnblogs.com/windlaughing/p/3241776.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的jar all下载地址:http://jackson.codehaus.org/1.7.6/jackson-all-1.7.6.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
因为下面的程序是用junit测试用例运行的,所以还得添加junit的jar包。版本是junit-4.2.8
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 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 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
* @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[/code]* @email hoojo_@126.com* @version 1.0*/@SuppressWarnings("unchecked")public class JacksonTest {private JsonGenerator jsonGenerator = null;private ObjectMapper objectMapper = null;private AccountBean bean = null;@Beforepublic void init() {bean = new AccountBean();bean.setAddress("china-Guangzhou");bean.setEmail("hoojo_@126.com");bean.setId(1);bean.setName("hoojo");objectMapper = new ObjectMapper();try {jsonGenerator = objectMapper.getJsonFactory().createJsonGenerator(System.out, JsonEncoding.UTF8);} catch (IOException e) {e.printStackTrace();}}@Afterpublic 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JavaEntitypackage com.hoo.entity;public class AccountBean {private int id;private String name;private String email;private String address;private Birthday birthday;//getter、setter@Overridepublic String toString() {return this.name + "#" + this.id + "#" + this.address + "#" + this.birthday + "#" + this.email;}}
Birthdaypackage com.hoo.entity;public class Birthday {private String birthday;public Birthday(String birthday) {super();this.birthday = birthday;}//getter、setterpublic Birthday() {}@Overridepublic String toString() {return this.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* @author hoojo* @createDate 2010-11-23 下午06:01:10*/@Testpublic void writeEntityJSON() {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 (IOException e) {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* @author hoojo* @createDate 2010-11-23 下午06:05:26*/@Testpublic 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("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 (IOException e) {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* @author hoojo* @createDate 2010-11-23 下午06:05:59*/@Testpublic 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###");//objectMapper list转换成JSON字符串objectMapper.writeValue(System.out, list);} catch (IOException e) {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"}]ObjectMapper1###[{"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。@Testpublic void writeOthersJSON() {try {String[] arr = { "a", "b", "c" };System.out.println("jsonGenerator");String str = "hello world jackson!";//bytejsonGenerator.writeBinary(str.getBytes());//booleanjsonGenerator.writeBoolean(true);//nulljsonGenerator.writeNull();//floatjsonGenerator.writeNumber(2.2f);//charjsonGenerator.writeRaw("c");//StringjsonGenerator.writeRaw(str, 5, 10);//StringjsonGenerator.writeRawValue(str, 5, 5);//StringjsonGenerator.writeString(str);jsonGenerator.writeTree(JsonNodeFactory.instance.POJONode(str));System.out.println();//ObjectjsonGenerator.writeStartObject();//{jsonGenerator.writeObjectFieldStart("user");//user:{jsonGenerator.writeStringField("name", "jackson");//name:jacksonjsonGenerator.writeBooleanField("sex", true);//sex:truejsonGenerator.writeNumberField("age", 22);//age:22jsonGenerator.writeEndObject();//}jsonGenerator.writeArrayFieldStart("infos");//infos:[jsonGenerator.writeNumber(22);//22jsonGenerator.writeString("this is array");//this is arrayjsonGenerator.writeEndArray();//]jsonGenerator.writeEndObject();//}AccountBean bean = new AccountBean();bean.setAddress("address");bean.setEmail("email");bean.setId(1);bean.setName("haha");//complex ObjectjsonGenerator.writeStartObject();//{jsonGenerator.writeObjectField("user", bean);//user:{bean}jsonGenerator.writeObjectField("infos", arr);//infos:[array]jsonGenerator.writeEndObject();//}} catch (Exception e) {e.printStackTrace();}}
运行后,结果如下: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@Testpublic 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:hahahaha#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>* @author hoojo* @createDate 2010-11-23 下午06:12:01*/@Testpublic 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();}}
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:2address:address2name:haha2id:2email:email2address:addressname:hahaid:1email: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* @author hoojo* @createDate 2010-11-23 下午06:14:01*/@Testpublic 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();}}
运行后的结果:2haha2#2#address2#null#email2haha#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* @author hoojo* @createDate Nov 27, 2010 3:00:06 PM*/@Testpublic 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();}}
运行后结果如下:3success:trueA:{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* @author hoojo* @createDate 2010-11-23 下午06:11:21*/@Testpublic void writeObject2Xml() {//stax2-api-3.0.2.jarSystem.out.println("XmlMapper");XmlMapper xml = new XmlMapper();try {//javaBean转换成xml//xml.writeValue(System.out, bean);StringWriter sw = new StringWriter();xml.writeValue(sw, bean);System.out.println(sw.toString());//List转换成xmlList<AccountBean> list = new ArrayList<AccountBean>();list.add(bean);list.add(bean);System.out.println(xml.writeValueAsString(list));//Map转换xml文档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();}}
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。
转自:http://www.cnblogs.com/hoojo/archive/2011/04/22/2024628.html
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