重载JsonMappingException以定制对错误JSON输入的异常返回信息

归纳能力不好，不知怎么写一个简洁的标题。。。

平台：Java, Jersey, Jackson

当restful api接收的json数据格式不对的时候，通常我们会返回异常信息，这些信息很有利于定位究竟是哪段json数据出了错。
我们也可以修改返回的信息。由于这些错误信息是框架给出的，所以可以通过重载相应的exception来定制返回的信息。
这么做有什么意义？要求比较严格的情况下，会不想让客户看到具体的信息，比如用到的包的信息（下面的错误信息中就包括包信息）；这些信息会被利用，进而分析是用什么实现的，进而利用这种实现潜在的漏洞进行攻击。

这么复杂的东西，对我来说不知道怎么实现，还好，可以参考这里：
http://javareferencegv.blogspot.com/2015/07/handle-invalid-json-request-by.html

我呢，用了一下，没问题；把整个方案记录一下：

假定一个restful pai，对应的输入参数的POJO是：

1. class mydata{
2. String name;
3. String[] days;
4. Map price;
5. }

正常的输入应该是：

1. {"name":"TOM","days":["20161223"],"things":{"apple":"11","orange:"12"}}

但是如果给的json数据是非法的，那么会抛出如下错误：

case 1:
输入：

1. {"name":"TOM","days":["20161223"],abcdefg,"things":{"apple":"11","orange:"12"}}

得到返回的错误信息：

1. Unexpected character ('a' (code 97)): was expecting double-quote to start field name at [Source: org.glassfish.jersey.message.internal.ReaderInterceptorExecutor$UnCloseableInputStream@7483; line: 1, column: 35]

case 2:
输入：

1. {"name":"TOM","days":"what","things":{"apple":"11","orange:"12"}}

得到返回的错误信息：

1. Can not deserialize instance of java.lang.String[] out of VALUE_STRING token at [Source: org.glassfish.jersey.message.internal.ReaderInterceptorExecutor$UnCloseableInputStream@983232; line: 1, column: 22] (through reference chain: xxx.yyy.mydata["days"])

case 3:
输入：

1. {"name":"TOM","days":["20161223"],"things":{"apple"}}

得到返回的错误信息：

1. Unexpected character ('}' (code 125)): was expecting a colon to separate field name and value at [Source: org.glassfish.jersey.message.internal.ReaderInterceptorExecutor$UnCloseableInputStream@7632323; line: 1, column: 51] at [Source: org.glassfish.jersey.message.internal.ReaderInterceptorExecutor$UnCloseableInputStream@2432432; line: 1, column: 55] (through reference chain: xxx.yyy.mydata["price"])

如果说不想给出这样详细的信息，而只是想提示一下有问题，那么可以通过重载相应的exception来做到。具体修改如下：

"web.xml"

1. <servlet>
   
2.         <servlet-name>myServlet</servlet-name>
   
3.         <servlet-class>
   
4.           org.glassfish.jersey.servlet.ServletContainer
   
5.         </servlet-class>
   
6.         <init-param>
   
7.           <param-name>javax.ws.rs.Application</param-name>
   
8.           <param-value>xxx.yyy.register</param-value>
   
9.         </init-param>
   
10.         <init-param>
    
11.             <param-name>
    
12.                 com.sun.jersey.api.json.POJOMappingFeature
    
13.             </param-name>
    
14.             <param-value>true</param-value>
    
15.         </init-param>
    
16.         <load-on-startup>1</load-on-startup>
    
17.     </servlet>

"xxx.yyy.register.java"

1. package xxx.yyy;
2. import java.io.File;
3. import org.codehaus.jackson.jaxrs.JacksonJsonProvider;
4. import org.glassfish.jersey.server.ResourceConfig;
5. import com.fasterxml.jackson.annotation.JsonInclude;
6. import com.fasterxml.jackson.annotation.JsonInclude.Include;
7. import com.fasterxml.jackson.jaxrs.json.JacksonJaxbJsonProvider;
8. import javax.ws.rs.ext.MessageBodyReader;
9. import javax.ws.rs.ext.MessageBodyWriter;
10. public class register extends ResourceConfig {
11. public register() {
12. packages("xxx.yyy");
13. register(YourJsonProvider.class);
14. register(MyJsonParseExceptionMapper.class);
15. register(MyJsonMappingExceptionMapper.class);
16. }
17. }

"MyJsonParseExceptionMapper.java"

1. package xxx.yyy;
2. import com.fasterxml.jackson.core.JsonParseException;
3. import javax.ws.rs.core.MediaType;
4. import javax.ws.rs.core.Response;
5. import javax.ws.rs.ext.ExceptionMapper;
6. import javax.ws.rs.ext.Provider;
7. @Provider
8. public class MyJsonParseExceptionMapper implements ExceptionMapper{
9. @Override
10. public Response toResponse(JsonParseException exception)
11. {
12. String info = "{\"Error\":\"It is an error, invalid JSON format.\"}";
13. return Response
14. .status(Response.Status.BAD_REQUEST)
15. .entity(info)
16. .type( MediaType.APPLICATION_JSON)
17. .build();
18. }
20. }

"MyJsonMappingExceptionMapper.java"

1. package xxx.yyy;
2. import com.fasterxml.jackson.databind.JsonMappingException;
3. import javax.ws.rs.core.MediaType;
4. import javax.ws.rs.core.Response;
5. import javax.ws.rs.ext.ExceptionMapper;
6. import javax.ws.rs.ext.Provider;
7. @Provider
8. public class MyJsonMappingExceptionMapper implements ExceptionMapper{
9. @Override
10. public Response toResponse(JsonMappingException exception)
11. {
12. String info = "{\"Error\":\"JSON format is OK, but some part's type is wrong.\"}";
13. return Response
14. .status(Response.Status.BAD_REQUEST)
15. .entity(info)
16. .type( MediaType.TEXT_PLAIN)
17. .build();
18. }
19. }

此时，再执行前面那几个错误的输入，可以得到如下输出：

case 1:
输入：

1. {"name":"TOM","days":["20161223"],abcdefg,"things":{"apple":"11","orange:"12"}}

输出：

1. {"Error":"It is an error, invalid JSON format."}

case 2:
输入：

1. {"name":"TOM","days":"what","things":{"apple":"11","orange:"12"}}

输出：

1. {"Error":"It is an error, invalid JSON format."}

case 3:
输入：

1. {"name":"TOM","days":["20161223"],"things":{"apple"}}

输出：

1. {"Error":"It is an error, invalid JSON format."}

用到的一些jar （其实不需要这么多）：

jackson-annotations-2.8.4.jar 
jackson-databind-2.8.4.jar   
jackson-jaxrs-json-provider-2.8.4.jar     
jackson-xc-1.9.2.jar
jackson-core-2.8.4.jar         
jackson-jaxrs-1.9.2.jar       
jackson-mapper-asl-1.9.2.jar
jackson-core-asl-1.9.2.jar     
jackson-jaxrs-base-2.8.4.jar 
jackson-module-jaxb-annotations-2.8.4.jar

javax.ws.rs-api-2.0.1.jar

jersey-client-2.25.jar             
jersey-container-servlet-core-2.25.jar 
jersey-guava-2.25.jar       
jersey-media-json-jackson-2.25.jar
jersey-common-2.25.jar             
jersey-core-1.19.3.jar                 
jersey-json-1.19.3.jar     
jersey-server-2.25.jar
jersey-container-servlet-2.25.jar 
jersey-entity-filtering-2.25.jar       
jersey-media-jaxb-2.25.jar

jsr305-3.0.0.jar