Jackson 使用简介

 

Jackson 使用简介
转自：http://jja1982.iteye.com/blog/764922

 

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最新jacson使用例子：

     需要3个包的支持：

     1. jackson-core-2.2.3.jar

     2. jackson-databind-2.2.3.jar

     3. jackson-annotations-2.2.3.jar

 public static String bean2Json(Object obj) throws IOException {

        ObjectMapper mapper = new ObjectMapper();

        StringWriter sw = new StringWriter();

        JsonGenerator gen = new JsonFactory().createJsonGenerator(sw);

        mapper.writeValue(gen, obj);

        gen.close();

        return sw.toString();

    }

    public static  T json2Bean(String jsonStr, Class objClass)

            throws JsonParseException, JsonMappingException, IOException {

        ObjectMapper mapper = new ObjectMapper();

        return mapper.readValue(jsonStr, objClass);

    }

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lib:
jackson-core-asl-1.6.0.jar
jackson-mapper-asl-1.6.0.jar

心得：最方便的是Full Data Binding方式，不用额外处理，但是POJO的属性名需要与JSON的变量名一一对应。对于需要做JSON变量名和POJO属性名转换的话，使用TreeModel。

Jackson提供了三种方式处理JSON
Streaming API， 基于事件处理JSON，类似StAXAPI。性能最好，其它两种方法都是建立在它之上
Tree Model 提供了内建文档树方式来展现JSON，类似XML DOM。最灵活。
Data Binding 使用注释或者属性访问器JSON与POJOs之间转换。最方便。

以下是官方网站的例子
1．Full Data Bindaing(POJO) Example
{
"name" : { "first" : "Joe", "last" : "Sixpack" },
"gender" : "MALE",
"verified" : false,
"userImage" : "Rm9vYmFyIQ=="
}

Java代码

1. public class User{
2. public enum Gender{
3. MALE, FEMALE
4. };
5. public static class Name{
6. private String _first,_last;
7. public String getFirst(){
8. return_first;
9. }
10. public String getLast(){
11. return_last;
12. }
13. public void setFirst(String s){
14. _first = s;
15. }
16. public void setLast(String s){
17. _last = s;
18. }
19. }
20. private Gender_gender;
21. private Name_name;
22. private boolean_isVerified;
23. private byte[]_userImage;
24. public Name getName(){
25. return_name;
26. }
27. public boolean isVerified(){
28. return_isVerified;
29. }
30. public Gender getGender(){
31. return_gender;
32. }
33. public byte[] getUserImage(){
34. return_userImage;
35. }
36. public void setName(Name n){
37. _name = n;
38. }
39. public voidsetVerified(boolean b){
40. _isVerified = b;
41. }
42. public void setGender(Gender g){
43. _gender = g;
44. }
45. public voidsetUserImage(byte[] b){
46. _userImage = b;
47. }
48. }

public class User {
        public enum Gender {
                MALE, FEMALE
        };

        public static class Name {
                private String _first, _last;

                public String getFirst() {
                        return _first;
                }

                public String getLast() {
                        return _last;
                }

                public void setFirst(String s) {
                        _first = s;
                }

                public void setLast(String s) {
                        _last = s;
                }
        }

        private Gender _gender;
        private Name _name;
        private boolean _isVerified;
        private byte[] _userImage;

        public Name getName() {
                return _name;
        }

        public boolean isVerified() {
                return _isVerified;
        }

        public Gender getGender() {
                return _gender;
        }

        public byte[] getUserImage() {
                return _userImage;
        }

        public void setName(Name n) {
                _name = n;
        }

        public void setVerified(boolean b) {
                _isVerified = b;
        }

        public void setGender(Gender g) {
                _gender = g;
        }

        public void setUserImage(byte[] b) {
                _userImage = b;
        }

}

Java代码

1. ObjectMapper mapper =newObjectMapper(); // canreuse, share globally
2. User user = mapper.readValue(newFile("user.json"),User.class);  //从文件中读取
3. mapper.writeValue(newFile("user-modified.json"),user);  //写入文件
4. mapper.writeValue(response.getOutputStream(),person);  //如果是servlet，这里是写入流中送到jsp页面

ObjectMapper mapper = new ObjectMapper(); // can reuse, share globally
User user = mapper.readValue(new File("user.json"), User.class);
mapper.writeValue(new File("user-modified.json"), user);

2．Simple Data Binding Example
Map userData = mapper.readValue(new File("user.json"),Map.class);
userData = new HashMap();
Map nameStruct = new HashMap();
nameStruct.put("first", "Joe");
nameStruct.put("last", "Sixpack");
userData.put("name", nameStruct);
userData.put("gender", "MALE");
userData.put("verified", Boolean.FALSE);
userData.put("userImage", "Rm9vYmFyIQ==");
mapper.writeValue(new File("user-modified.json"), userData);
Concrete Java types that Jackson will use for simple data bindingare:

JSON Type	Java Type
object	LinkedHashMap
array	ArrayList
string	String
number (no fraction)	Integer, Long or BigInteger (smallest applicable)
number (fraction)	Double (configurable to use BigDecimal)
true false	Boolean
null	null

3．The Model Example

Java代码

1. ObjectMapper m = newObjectMapper();
2. // can either usemapper.readTree(JsonParser), or bind toJsonNode
3. JsonNode rootNode =m.readValue(newFile("user.json"),JsonNode.class);
4. // ensure that "last name"isn't "Xmler"; if is, change to "Jsoner"
5. JsonNode nameNode = rootNode.path("name");
6. String lastName = nameNode.path("last").getTextValue();
7. if("xmler".equalsIgnoreCase(lastName)){
8. ((ObjectNode)nameNode).put("last", "Jsoner");
9. }
10. // and write itout:
11. m.writeValue(newFile("user-modified.json"),rootNode);

 

 

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[代码] 首先创建一个User对象类(User.java)

01	package com.sivalabs.json;

02

03	import java.util.Date;

04

05	public class User {

06	privateString userId;

07	privateUserName userName;

08	private Datedob;

09

10

@Override

11	public StringtoString(){

12	return"User [dob=" + dob + ",userId=" + userId + ",userName="+ userName +"]";

13

}

14	//setters andgetters

15

16

}

[代码] UserName.java

01	package com.sivalabs.json;

02

03	public class UserName{

04	privateString firstname;

05	privateString middlename;

06	privateString lastname;

07

08

@Override

09	public StringtoString()

10

{

11	return"UserName [firstname=" + firstname+

12	",lastname=" + lastname+

13	",middlename=" + middlename +"]";

14

}

15	//setters andgetters

16

}

[代码] [Java]代码

01	//接下来创建User实例，并生成JSON数据

02

03	ObjectMapper mapper = newObjectMapper();

04

05	UserName userName = newUserName();

06	userName.setFirstname("Katamreddy");

07	userName.setMiddlename("Siva");

08	userName.setLastname("PrasadReddy");

09

10	User user = newUser();

11	user.setUserId("1");

12	user.setUserName(userName);

13	user.setDob(newDate());

14

15	Writer strWriter = newStringWriter();

16	mapper.writeValue(strWriter, user);

17	String userDataJSON = strWriter.toString();

18	System.out.println(userDataJSON);

[代码] 执行结果

01

{

02	"userId":"1",

03	"userName":

04

{

05	"firstname":"Katamreddy",

06	"middlename":"Siva",

07	"lastname":"PrasadReddy"

08

},

09	"dob":1300878089906

10

}

[代码] 接下来进行JSON到Java对象的转换

1	String userDataJSON =

2	"{"userId":"100","userName":{"firstname":"K""+

3	","middlename":"Siva","lastname":"Prasad"},"dob":1300878089906}";

4	User userFromJSON = mapper.readValue(userDataJSON,User.class);

5	System.out.println(userFromJSON);

[代码] 时间的格式化处理

1	DateFormat dateFormat = newSimpleDateFormat("MM-dd-yyyy");

2	SerializationConfig serConfig =mapper.getSerializationConfig();

3	serConfig.setDateFormat(dateFormat);

4	DeserializationConfig deserializationConfig =mapper.getDeserializationConfig();

5	deserializationConfig.setDateFormat(dateFormat);

6	mapper.configure(SerializationConfig.Feature.WRITE_DATES_AS_TIMESTAMPS,false);

[代码] [Java]代码

1	//从文件中读取JSON数据

2	User user = mapper.readValue(newFile("user.json"),User.class);