Jackson 框架,轻易转换JSON
2015-07-21 15:22
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前面有介绍过json-lib这个框架,在线博文:
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jarall下载地址:
然后在工程中导入这个jar包即可开始工作
官方示例:
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
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;@Beforepublicvoidinit(){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();}}@Afterpublicvoiddestory(){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JavaEntitypackagecom.hoo.entity;publicclassAccountBean{privateintid;privateStringname;privateStringemail;privateStringaddress;privateBirthdaybirthday;//getter、setter@OverridepublicStringtoString(){returnthis.name+"#"+this.id+"#"+this.address+"#"+this.birthday+"#"+this.email;}}
Birthdaypackagecom.hoo.entity;publicclassBirthday{privateStringbirthday;publicBirthday(Stringbirthday){super();this.birthday=birthday;}//getter、setterpublicBirthday(){}@OverridepublicStringtoString(){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*/@TestpublicvoidwriteEntityJSON(){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*/@TestpublicvoidwriteMapJSON(){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*/@TestpublicvoidwriteListJSON(){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"}]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。@TestpublicvoidwriteOthersJSON(){try{String[]arr={"a","b","c"};System.out.println("jsonGenerator");Stringstr="helloworldjackson!";//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("thisisarray");//thisisarrayjsonGenerator.writeEndArray();//]jsonGenerator.writeEndObject();//}AccountBeanbean=newAccountBean();bean.setAddress("address");bean.setEmail("email");bean.setId(1);bean.setName("haha");//complexObjectjsonGenerator.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@TestpublicvoidreadJson2Entity(){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: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>*@authorhoojo*@createDate2010-11-23下午06:12:01*/@TestpublicvoidreadJson2List(){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: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*@authorhoojo*@createDate2010-11-23下午06:14:01*/@TestpublicvoidreadJson2Array(){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: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*@authorhoojo*@createDateNov27,20103:00:06PM*/@TestpublicvoidreadJson2Map(){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: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*@authorhoojo*@createDate2010-11-23下午06:11:21*/@TestpublicvoidwriteObject2Xml(){//stax2-api-3.0.2.jarSystem.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xmlList<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。
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