Jackson可以輕鬆的將Java對象轉換成json對象和xml文檔，同樣也可以將json、xml轉換成Java對象。
前面有介紹過json-lib這個框架，在線博文：http://www.cnblogs.com/hoojo/archive/2011/04/21/2023805.html
相比json-lib框架，Jackson所依賴的jar包較少，簡單易用並且性能也要相對高些。而且Jackson社區相對比較活躍，更新速度也比較快。
一、準備工作
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包即可開始工作
官方示例：http://wiki.fasterxml.com/JacksonInFiveMinutes
因爲下面的程序是用junit測試用例運行的，所以還得添加junit的jar包。版本是junit-4.2.8
如果你需要轉換xml，那麼還需要stax2-api.jar
2、 測試類基本代碼如下
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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 * @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 * @email hoojo_@126.com * @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對象轉換成JSON
1、 JavaBean(Entity/Model)轉換成JSON
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/** * <b>function:</b>將java對象轉換成json字符串 * @author hoojo * @createDate 2010-11-23 下午06:01:10 */ @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相同的功能 objectMapper.writeValue(System.out, bean); } catch (IOException e) { e.printStackTrace(); } } |
運行後結果如下：
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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]"} |
上面分別利用JsonGenerator的writeObject方法和ObjectMapper的writeValue方法完成對Java對象的轉換，二者傳遞的參數及構造的方式不同；JsonGenerator的創建依賴於ObjectMapper對象。也就是說如果你要使用JsonGenerator來轉換JSON，那麼你必須創建一個ObjectMapper。但是你用ObjectMapper來轉換JSON，則不需要JSONGenerator。
objectMapper的writeValue方法可以將一個Java對象轉換成JSON。這個方法的參數一，需要提供一個輸出流，轉換後可以通過這個流來輸出轉換後的內容。或是提供一個File，將轉換後的內容寫入到File中。當然，這個參數也可以接收一個JSONGenerator，然後通過JSONGenerator來輸出轉換後的信息。第二個參數是將要被轉換的Java對象。如果用三個參數的方法，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對象的某些屬性進行過濾或轉換等。
2、 將Map集合轉換成Json字符串
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/** * <b>function:</b>將map轉換成json字符串 * @author hoojo * @createDate 2010-11-23 下午06:05:26 */ @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(); } } |
轉換後結果如下：
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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":"[email protected]"}} |
3、 將List集合轉換成json
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/** * <b>function:</b>將list集合轉換成json字符串 * @author hoojo * @createDate 2010-11-23 下午06:05:59 */ @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直接返回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(); } } |
結果如下：
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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"}] |
外面就是多了個[]中括號；同樣Array也可以轉換，轉換的JSON和上面的結果是一樣的，這裏就不再轉換了。~.~
4、下面來看看jackson提供的一些類型，用這些類型完成json轉換；如果你使用這些類型轉換JSON的話，那麼你即使沒有JavaBean(Entity)也可以完成複雜的Java類型的JSON轉換。下面用到這些類型構建一個複雜的Java對象，並完成JSON轉換。
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@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(); } } |
運行後，結果如下：
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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"]} |
怎麼樣？構造的json字符串和輸出的結果是一致的吧。關鍵看懂用JSONGenerator提供的方法，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
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@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(); } } |
很簡單，用到了ObjectMapper這個對象的readValue這個方法，這個方法需要提供2個參數。第一個參數就是解析的JSON字符串，第二個參數是即將將這個JSON解析吃什麼Java對象，Java對象的類型。當然，還有其他相同簽名方法，如果你有興趣可以一一嘗試使用方法，當然使用的方法和當前使用的方法大同小異。運行後，結果如下：
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haha haha#1#address#null#email |
2、 將json字符串轉換成List<Map>集合
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/** * <b>function:</b>json字符串轉換成list<map> * @author hoojo * @createDate 2010-11-23 下午06:12:01 */ @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(); } } |
嘗試過將上面的JSON轉換成List，然後List中存放AccountBean，但結果失敗了。但是支持Map集合。因爲你轉成List.class，但是不知道List存放何種類型。只好默然Map類型。因爲所有的對象都可以轉換成Map結合，運行後結果如下：
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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，由於上面的泛型轉換不能識別到集合中的對象類型。所有這裏用對象數組，可以解決這個問題。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。
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/** * <b>function:</b>json字符串轉換成Array * @author hoojo * @createDate 2010-11-23 下午06:14:01 */ @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(); } } |
運行後的結果：
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2 haha2#2#address2#null#email2 haha#1#address#null#email |
4、 Json字符串轉換成Map集合
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/** * <b>function:</b>json字符串轉換Map集合 * @author hoojo * @createDate Nov 27, 2010 3:00:06 PM */ @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(); } } |
運行後結果如下：
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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，轉換後的結果要比json-lib更直觀，不過它依賴於stax2-api.jar這個jar包。
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/** * <b>function:</b>java對象轉換成xml文檔 * 需要額外的jar包 stax2-api.jar * @author hoojo * @createDate 2010-11-23 下午06:11:21 */ @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(); } } |
運行上面的方法，結果如下：
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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> |
看結果，根節點都是unknown 這個問題還沒有解決，由於根節點沒有轉換出來，所有導致解析xml到Java對象，也無法完成。