Jackson 使用简介

 

http://jackson.codehaus.org/

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Tree Model。

Jackson提供了三种方式处理JSON
Streaming API ， 基于事件处理JSON，类似StAX API。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=="
}

 

  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;  
      }  
    
  }  

 

 

 

 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);  

 

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<String, Object> userData = mapper.readValue(new File("user.json"), Map.class);
userData = new HashMap<String, Object>();
Map<String, String> nameStruct = new HashMap<String, String>();
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 binding are:

JSON Type	Java Type
object	LinkedHashMap<String,Object>
array	ArrayList<Object>
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

ObjectMapper m = new ObjectMapper();  
// can either use mapper.readTree(JsonParser), or bind to JsonNode  
JsonNode rootNode = m.readValue(new File("user.json"), JsonNode.class);  
// ensure that "last name" isn't "Xmler"; if is, change to "Jsoner"  
JsonNode nameNode = rootNode.path("name");  
String lastName = nameNode.path("last").getTextValue();  
if ("xmler".equalsIgnoreCase(lastName)) {  
    ((ObjectNode)nameNode).put("last", "Jsoner");  
}  
// and write it out:  
m.writeValue(new File("user-modified.json"), rootNode);