Jackson可变插值反序列化

Question

如何自定义Jackson反序列化一个包含${token}的值？

这里是我想从Apache Commons Configuration variable interpolation添加functionnality的例子：

{ 
    "file" = "${sys:user.home}/path/to/my_file" 
} 

Answer 1

您可以注册custom string deserialiser基于这将在deserialisation后插值变量的默认。

但是，正如在评论中指出的那样，这对于诸如文件和URL之类的非字符串类型不起作用。更好的想法是通过传递定制的JsonFactory来覆盖JsonParser的getText()和getValueAsString()方法。

下面是一个例子：

public class JacksonInterpolateString { 
    static final String JSON = "{ \"file\":\"${sys:user.home}/path/to/my_file\" }"; 

    public static class Bean { 
     public File file; 

     @Override 
     public String toString() { 
      return file.toString(); 
     } 
    } 

    private static class MyJsonParser extends JsonParserDelegate { 

     public MyJsonParser(final JsonParser d) { 
      super(d); 
     } 

     @Override 
     public String getText() throws IOException { 
      final String value = super.getText(); 
      if (value != null) { 
       return interpolateString(value); 
      } 
      return value; 
     } 

     @Override 
     public String getValueAsString() throws IOException { 
      return getValueAsString(null); 
     } 

     @Override 
     public String getValueAsString(final String defaultValue) throws IOException { 
      final String value = super.getValueAsString(defaultValue); 
      if (value != null) { 
       return interpolateString(value); 
      } 
      return null; 
     } 
    } 

    private static class MyMappingJsonFactory extends MappingJsonFactory { 
     @Override 
     protected JsonParser _createParser(
       final char[] data, 
       final int offset, 
       final int len, 
       final IOContext ctxt, 
       final boolean recyclable) 
       throws IOException { 
      return new MyJsonParser(super._createParser(data, offset, len, ctxt, recyclable)); 
     } 

     @Override 
     protected JsonParser _createParser(final Reader r, final IOContext ctxt) 
       throws IOException { 
      return new MyJsonParser(super._createParser(r, ctxt)); 
     } 

    } 

    private static String interpolateString(final String value) { 
     return value.replace("${sys:user.home}", "/home/user"); 
    } 

    public static void main(String[] args) throws IOException { 
     final JsonFactory factory = new MyMappingJsonFactory(); 
     final ObjectMapper mapper = new ObjectMapper(factory); 
     System.out.println(mapper.readValue(JSON, Map.class)); 
     System.out.println(mapper.readValue(JSON, Bean.class)); 
    } 

} 

输出：

{file=/home/user/path/to/my_file} 
/home/user/path/to/my_file