Jackson可以輕松的將Java對(duì)象轉(zhuǎn)換成json對(duì)象和xml文檔，同樣也可以將json、xml轉(zhuǎn)換成Java對(duì)象。
相比json-lib框架，Jackson所依賴的jar包較少，簡(jiǎn)單易用并且性能也要相對(duì)高些。而且Jackson社區(qū)相對(duì)比較活躍，更新速度也比較快。
一、準(zhǔn)備工作
1、 下載依賴庫(kù)jar包
Jackson的jar all下載地址：http://jackson.codehaus.org/1.7.6/jackson-all-1.7.6.jar
然后在工程中導(dǎo)入這個(gè)jar包即可開(kāi)始工作
官方示例：http://wiki.fasterxml.com/JacksonInFiveMinutes
因?yàn)橄旅娴某绦蚴怯胘unit測(cè)試用例運(yùn)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(zhuǎn)換xml，那么還需要stax2-api.jar
2、 測(cè)試類基本代碼如下
java" id="highlighter_287132">
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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(duì)象轉(zhuǎn)換成JSON字符串，也可以將JSON字符串轉(zhuǎn)換成java對(duì)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.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
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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
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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(duì)象轉(zhuǎn)換成JSON
1、 JavaBean(Entity/Model)轉(zhuǎn)換成JSON
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/** * function:將java對(duì)象轉(zhuǎn)換成json字符串 * @author hoojo */@Testpublic void writeEntityJSON() { try { System.out.println("jsonGenerator"); //writeObject可以轉(zhuǎn)換java對(duì)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(yùn)行后結(jié)果如下：
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jsonGeneratorObjectMapper{"address":"china-Guangzhou","name":"hoojo","id":1,"birthday":null,"email":<a href="mailto:[email protected]" rel="external nofollow">[email protected]</a>} |
上面分別利用JsonGenerator的writeObject方法和ObjectMapper的writeValue方法完成對(duì)Java對(duì)象的轉(zhuǎn)換，二者傳遞的參數(shù)及構(gòu)造的方式不同；JsonGenerator的創(chuàng)建依賴于ObjectMapper對(duì)象。也就是說(shuō)如果你要使用JsonGenerator來(lái)轉(zhuǎn)換JSON，那么你必須創(chuàng)建一個(gè)ObjectMapper。但是你用ObjectMapper來(lái)轉(zhuǎn)換JSON，則不需要JSONGenerator。
objectMapper的writeValue方法可以將一個(gè)Java對(duì)象轉(zhuǎn)換成JSON。這個(gè)方法的參數(shù)一，需要提供一個(gè)輸出流，轉(zhuǎn)換后可以通過(guò)這個(gè)流來(lái)輸出轉(zhuǎn)換后的內(nèi)容。或是提供一個(gè)File，將轉(zhuǎn)換后的內(nèi)容寫(xiě)入到File中。當(dāng)然，這個(gè)參數(shù)也可以接收一個(gè)JSONGenerator，然后通過(guò)JSONGenerator來(lái)輸出轉(zhuǎn)換后的信息。第二個(gè)參數(shù)是將要被轉(zhuǎn)換的Java對(duì)象。如果用三個(gè)參數(shù)的方法，那么是一個(gè)Config。這個(gè)config可以提供一些轉(zhuǎn)換時(shí)的規(guī)則，過(guò)指定的Java對(duì)象的某些屬性進(jìn)行過(guò)濾或轉(zhuǎn)換等。
2、 將Map集合轉(zhuǎn)換成Json字符串
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/** * <b>function:</b>將map轉(zhuǎn)換成json字符串 * @author hoojo */@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"); 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(zhuǎn)換后結(jié)果如下：
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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":<a href="mailto:[email protected]" rel="external nofollow">[email protected]</a>}} |
3、 將List集合轉(zhuǎn)換成json
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/** * <b>function:</b>將list集合轉(zhuǎn)換成json字符串 * @author hoojo */@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轉(zhuǎn)換成JSON字符串 jsonGenerator.writeObject(list); System.out.println(); System.out.println("ObjectMapper"); //用objectMapper直接返回list轉(zhuǎn)換成的JSON字符串 System.out.println("1###" + objectMapper.writeValueAsString(list)); System.out.print("2###"); //objectMapper list轉(zhuǎn)換成JSON字符串 objectMapper.writeValue(System.out, list); } catch (IOException e) { e.printStackTrace(); }} |
結(jié)果如下：
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jsonGenerator{"address":"address2","name":"haha2","id":2,"birthday":null,"email":"email2"}]ObjectMapper1###[{"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(gè)[]中括號(hào)；同樣Array也可以轉(zhuǎn)換，轉(zhuǎn)換的JSON和上面的結(jié)果是一樣的，這里就不再轉(zhuǎn)換了。~.~
4、下面來(lái)看看jackson提供的一些類型，用這些類型完成json轉(zhuǎn)換；如果你使用這些類型轉(zhuǎn)換JSON的話，那么你即使沒(méi)有JavaBean(Entity)也可以完成復(fù)雜的Java類型的JSON轉(zhuǎn)換。下面用到這些類型構(gòu)建一個(gè)復(fù)雜的Java對(duì)象，并完成JSON轉(zhuǎn)換。
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@Testpublic 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(yùn)行后，結(jié)果如下：
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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"]} |
怎么樣？構(gòu)造的json字符串和輸出的結(jié)果是一致的吧。關(guān)鍵看懂用JSONGenerator提供的方法，完成一個(gè)Object的構(gòu)建。
三、JSON轉(zhuǎn)換成Java對(duì)象
1、 將json字符串轉(zhuǎn)換成JavaBean對(duì)象
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@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(); }} |
很簡(jiǎn)單，用到了ObjectMapper這個(gè)對(duì)象的readValue這個(gè)方法，這個(gè)方法需要提供2個(gè)參數(shù)。第一個(gè)參數(shù)就是解析的JSON字符串，第二個(gè)參數(shù)是即將將這個(gè)JSON解析吃什么Java對(duì)象，Java對(duì)象的類型。當(dāng)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(dāng)然使用的方法和當(dāng)前使用的方法大同小異。運(yùn)行后，結(jié)果如下：
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hahahaha#1#address#null#email |
2、 將json字符串轉(zhuǎn)換成List<Map>集合
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/** * <b>function:</b>json字符串轉(zhuǎn)換成list<map> * @author hoojo */@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(); }} |
嘗試過(guò)將上面的JSON轉(zhuǎn)換成List，然后List中存放AccountBean，但結(jié)果失敗了。但是支持Map集合。因?yàn)槟戕D(zhuǎn)成List.class，但是不知道List存放何種類型。只好默然Map類型。因?yàn)樗械膶?duì)象都可以轉(zhuǎn)換成Map結(jié)合，運(yùn)行后結(jié)果如下：
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2address:address2name:haha2id:2email:email2address:addressname:hahaid:1email:email |
3、 Json字符串轉(zhuǎn)換成Array數(shù)組，由于上面的泛型轉(zhuǎn)換不能識(shí)別到集合中的對(duì)象類型。所有這里用對(duì)象數(shù)組，可以解決這個(gè)問(wèn)題。只不過(guò)它不再是集合，而是一個(gè)數(shù)組。當(dāng)然這個(gè)不重要，你可以用Arrays.asList將其轉(zhuǎn)換成List即可。
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/** * <b>function:</b>json字符串轉(zhuǎn)換成Array * @author hoojo */@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(); }} |
運(yùn)行后的結(jié)果：
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2haha2#2#address2#null#email2haha#1#address#null#email |
4、 Json字符串轉(zhuǎn)換成Map集合
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/** * <b>function:</b>json字符串轉(zhuǎn)換Map集合 * @author hoojo */@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(); }} |
運(yùn)行后結(jié)果如下：
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3success:trueA:{address=address2, name=haha2, id=2, email=email2}B:{address=address, name=haha, id=1, email=email} |
四、Jackson對(duì)XML的支持
Jackson也可以完成java對(duì)象到xml的轉(zhuǎn)換，轉(zhuǎn)換后的結(jié)果要比json-lib更直觀，不過(guò)它依賴于stax2-api.jar這個(gè)jar包。
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/** * <b>function:</b>java對(duì)象轉(zhuǎn)換成xml文檔 * 需要額外的jar包 stax2-api.jar * @author hoojo */@Testpublic void writeObject2Xml() { //stax2-api-3.0.2.jar System.out.println("XmlMapper"); XmlMapper xml = new XmlMapper(); try { //javaBean轉(zhuǎn)換成xml //xml.writeValue(System.out, bean); StringWriter sw = new StringWriter(); xml.writeValue(sw, bean); System.out.println(sw.toString()); //List轉(zhuǎn)換成xml List<AccountBean> list = new ArrayList<AccountBean>(); list.add(bean); list.add(bean); System.out.println(xml.writeValueAsString(list)); //Map轉(zhuǎn)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(yùn)行上面的方法，結(jié)果如下：
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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> |
看結(jié)果，根節(jié)點(diǎn)都是unknown 這個(gè)問(wèn)題還沒(méi)有解決，由于根節(jié)點(diǎn)沒(méi)有轉(zhuǎn)換出來(lái)，所有導(dǎo)致解析xml到Java對(duì)象，也無(wú)法完成。
以上就是本文的全部?jī)?nèi)容，希望對(duì)大家的學(xué)習(xí)有所幫助，也希望大家多多支持服務(wù)器之家。
原文鏈接：http://www.cnblogs.com/hoojo/archive/2011/04/22/2024628.html
