How to customize parameter names when binding Spring MVC command objects?

I have a command object:

public class Job {
    private String jobType;
    private String location;
}

Which is bound by spring-mvc:

@RequestMapping("/foo")
public String doSomethingWithJob(Job job) {
   ...
}

Which works fine for http://example.com/foo?jobType=permanent&location=Stockholm. But now I need to make it work for the following url instead:

http://example.com/foo?jt=permanent&loc=Stockholm

Obviously, I don't want to change my command object, because the field names have to remain long (as they are used in the code). How can I customize that? Is there an option to do something like this:

public class Job {
    @RequestParam("jt")
    private String jobType;
    @RequestParam("loc")
    private String location;
}

This doesn't work (@RequestParam can't be applied to fields).

The thing I'm thinking about is a custom message converter similar to FormHttpMessageConverter and read a custom annotation on the target object

Solution 1:

This solution more concise but requires using RequestMappingHandlerAdapter, which Spring use when <mvc:annotation-driven /> enabled. Hope it will help somebody. The idea is to extend ServletRequestDataBinder like this:

 /**
 * ServletRequestDataBinder which supports fields renaming using {@link ParamName}
 *
 * @author jkee
 */
public class ParamNameDataBinder extends ExtendedServletRequestDataBinder {

    private final Map<String, String> renameMapping;

    public ParamNameDataBinder(Object target, String objectName, Map<String, String> renameMapping) {
        super(target, objectName);
        this.renameMapping = renameMapping;
    }

    @Override
    protected void addBindValues(MutablePropertyValues mpvs, ServletRequest request) {
        super.addBindValues(mpvs, request);
        for (Map.Entry<String, String> entry : renameMapping.entrySet()) {
            String from = entry.getKey();
            String to = entry.getValue();
            if (mpvs.contains(from)) {
                mpvs.add(to, mpvs.getPropertyValue(from).getValue());
            }
        }
    }
}

Appropriate processor:

/**
 * Method processor supports {@link ParamName} parameters renaming
 *
 * @author jkee
 */

public class RenamingProcessor extends ServletModelAttributeMethodProcessor {

    @Autowired
    private RequestMappingHandlerAdapter requestMappingHandlerAdapter;

    //Rename cache
    private final Map<Class<?>, Map<String, String>> replaceMap = new ConcurrentHashMap<Class<?>, Map<String, String>>();

    public RenamingProcessor(boolean annotationNotRequired) {
        super(annotationNotRequired);
    }

    @Override
    protected void bindRequestParameters(WebDataBinder binder, NativeWebRequest nativeWebRequest) {
        Object target = binder.getTarget();
        Class<?> targetClass = target.getClass();
        if (!replaceMap.containsKey(targetClass)) {
            Map<String, String> mapping = analyzeClass(targetClass);
            replaceMap.put(targetClass, mapping);
        }
        Map<String, String> mapping = replaceMap.get(targetClass);
        ParamNameDataBinder paramNameDataBinder = new ParamNameDataBinder(target, binder.getObjectName(), mapping);
        requestMappingHandlerAdapter.getWebBindingInitializer().initBinder(paramNameDataBinder, nativeWebRequest);
        super.bindRequestParameters(paramNameDataBinder, nativeWebRequest);
    }

    private static Map<String, String> analyzeClass(Class<?> targetClass) {
        Field[] fields = targetClass.getDeclaredFields();
        Map<String, String> renameMap = new HashMap<String, String>();
        for (Field field : fields) {
            ParamName paramNameAnnotation = field.getAnnotation(ParamName.class);
            if (paramNameAnnotation != null && !paramNameAnnotation.value().isEmpty()) {
                renameMap.put(paramNameAnnotation.value(), field.getName());
            }
        }
        if (renameMap.isEmpty()) return Collections.emptyMap();
        return renameMap;
    }
}

Annotation:

/**
 * Overrides parameter name
 * @author jkee
 */

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface ParamName {

    /**
     * The name of the request parameter to bind to.
     */
    String value();

}

Spring config:

<mvc:annotation-driven>
    <mvc:argument-resolvers>
        <bean class="ru.yandex.metrika.util.params.RenamingProcessor">
            <constructor-arg name="annotationNotRequired" value="true"/>
        </bean>
    </mvc:argument-resolvers>
</mvc:annotation-driven> 

And finally, usage (like Bozho solution):

public class Job {
    @ParamName("job-type")
    private String jobType;
    @ParamName("loc")
    private String location;
}

Solution 2:

Here's what I got working:

First, a parameter resolver:

/**
 * This resolver handles command objects annotated with @SupportsAnnotationParameterResolution
 * that are passed as parameters to controller methods.
 * 
 * It parses @CommandPerameter annotations on command objects to
 * populate the Binder with the appropriate values (that is, the filed names
 * corresponding to the GET parameters)
 * 
 * In order to achieve this, small pieces of code are copied from spring-mvc
 * classes (indicated in-place). The alternative to the copied lines would be to
 * have a decorator around the Binder, but that would be more tedious, and still
 * some methods would need to be copied.
 * 
 * @author bozho
 * 
 */
public class AnnotationServletModelAttributeResolver extends ServletModelAttributeMethodProcessor {

    /**
     * A map caching annotation definitions of command objects (@CommandParameter-to-fieldname mappings)
     */
    private ConcurrentMap<Class<?>, Map<String, String>> definitionsCache = Maps.newConcurrentMap();

    public AnnotationServletModelAttributeResolver(boolean annotationNotRequired) {
        super(annotationNotRequired);
    }

    @Override
    public boolean supportsParameter(MethodParameter parameter) {
        if (parameter.getParameterType().isAnnotationPresent(SupportsAnnotationParameterResolution.class)) {
            return true;
        }
        return false;
    }

    @Override
    protected void bindRequestParameters(WebDataBinder binder, NativeWebRequest request) {
        ServletRequest servletRequest = request.getNativeRequest(ServletRequest.class);
        ServletRequestDataBinder servletBinder = (ServletRequestDataBinder) binder;
        bind(servletRequest, servletBinder);
    }

    @SuppressWarnings("unchecked")
    public void bind(ServletRequest request, ServletRequestDataBinder binder) {
        Map<String, ?> propertyValues = parsePropertyValues(request, binder);
        MutablePropertyValues mpvs = new MutablePropertyValues(propertyValues);
        MultipartRequest multipartRequest = WebUtils.getNativeRequest(request, MultipartRequest.class);
        if (multipartRequest != null) {
            bindMultipart(multipartRequest.getMultiFileMap(), mpvs);
        }

        // two lines copied from ExtendedServletRequestDataBinder
        String attr = HandlerMapping.URI_TEMPLATE_VARIABLES_ATTRIBUTE;
        mpvs.addPropertyValues((Map<String, String>) request.getAttribute(attr));
        binder.bind(mpvs);
    }

    private Map<String, ?> parsePropertyValues(ServletRequest request, ServletRequestDataBinder binder) {

        // similar to WebUtils.getParametersStartingWith(..) (prefixes not supported)
        Map<String, Object> params = Maps.newTreeMap();
        Assert.notNull(request, "Request must not be null");
        Enumeration<?> paramNames = request.getParameterNames();
        Map<String, String> parameterMappings = getParameterMappings(binder);
        while (paramNames != null && paramNames.hasMoreElements()) {
            String paramName = (String) paramNames.nextElement();
            String[] values = request.getParameterValues(paramName);

            String fieldName = parameterMappings.get(paramName);
            // no annotation exists, use the default - the param name=field name
            if (fieldName == null) {
                fieldName = paramName;
            }

            if (values == null || values.length == 0) {
                // Do nothing, no values found at all.
            } else if (values.length > 1) {
                params.put(fieldName, values);
            } else {
                params.put(fieldName, values[0]);
            }
        }

        return params;
    }

    /**
     * Gets a mapping between request parameter names and field names.
     * If no annotation is specified, no entry is added
     * @return
     */
    private Map<String, String> getParameterMappings(ServletRequestDataBinder binder) {
        Class<?> targetClass = binder.getTarget().getClass();
        Map<String, String> map = definitionsCache.get(targetClass);
        if (map == null) {
            Field[] fields = targetClass.getDeclaredFields();
            map = Maps.newHashMapWithExpectedSize(fields.length);
            for (Field field : fields) {
                CommandParameter annotation = field.getAnnotation(CommandParameter.class);
                if (annotation != null && !annotation.value().isEmpty()) {
                    map.put(annotation.value(), field.getName());
                }
            }
            definitionsCache.putIfAbsent(targetClass, map);
            return map;
        } else {
            return map;
        }
    }

    /**
     * Copied from WebDataBinder.
     * 
     * @param multipartFiles
     * @param mpvs
     */
    protected void bindMultipart(Map<String, List<MultipartFile>> multipartFiles, MutablePropertyValues mpvs) {
        for (Map.Entry<String, List<MultipartFile>> entry : multipartFiles.entrySet()) {
            String key = entry.getKey();
            List<MultipartFile> values = entry.getValue();
            if (values.size() == 1) {
                MultipartFile value = values.get(0);
                if (!value.isEmpty()) {
                    mpvs.add(key, value);
                }
            } else {
                mpvs.add(key, values);
            }
        }
    }
}

And then registering the parameter resolver using a post-processor. It should be registered as a <bean>:

/**
 * Post-processor to be used if any modifications to the handler adapter need to be made
 * 
 * @author bozho
 *
 */
public class AnnotationHandlerMappingPostProcessor implements BeanPostProcessor {

    @Override
    public Object postProcessAfterInitialization(Object bean, String arg1)
            throws BeansException {
        return bean;
    }

    @Override
    public Object postProcessBeforeInitialization(Object bean, String arg1)
            throws BeansException {
        if (bean instanceof RequestMappingHandlerAdapter) {
            RequestMappingHandlerAdapter adapter = (RequestMappingHandlerAdapter) bean;
            List<HandlerMethodArgumentResolver> resolvers = adapter.getCustomArgumentResolvers();
            if (resolvers == null) {
                resolvers = Lists.newArrayList();
            }
            resolvers.add(new AnnotationServletModelAttributeResolver(false));
            adapter.setCustomArgumentResolvers(resolvers);
        }

        return bean;
    }

}

Solution 3:

In Spring 3.1, ServletRequestDataBinder provides a hook for additional bind values:

protected void addBindValues(MutablePropertyValues mpvs, ServletRequest request) {
}

The ExtendedServletRequestDataBinder subclass uses it to add URI template variables as binding values. You could extend it further to make it possible to add command-specific field aliases.

You can override RequestMappingHandlerAdapter.createDataBinderFactory(..) to provide a custom WebDataBinder instance. From a controller's perspective it could look like this:

@InitBinder
public void initBinder(MyWebDataBinder binder) {
   binder.addFieldAlias("jobType", "jt");
   // ...
}

Solution 4:

Thanks the answer of @jkee .
Here is my solution.
First, a custom annotation:

@Inherited
@Documented
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface ParamName {

  /**
   * The name of the request parameter to bind to.
   */
  String value();

}

A customer DataBinder:

public class ParamNameDataBinder extends ExtendedServletRequestDataBinder {

  private final Map<String, String> paramMappings;

  public ParamNameDataBinder(Object target, String objectName, Map<String, String> paramMappings) {
    super(target, objectName);
    this.paramMappings = paramMappings;
  }

  @Override
  protected void addBindValues(MutablePropertyValues mutablePropertyValues, ServletRequest request) {
    super.addBindValues(mutablePropertyValues, request);
    for (Map.Entry<String, String> entry : paramMappings.entrySet()) {
      String paramName = entry.getKey();
      String fieldName = entry.getValue();
      if (mutablePropertyValues.contains(paramName)) {
        mutablePropertyValues.add(fieldName, mutablePropertyValues.getPropertyValue(paramName).getValue());
      }
    }
  }

}

A parameter resolver:

public class ParamNameProcessor extends ServletModelAttributeMethodProcessor {

  @Autowired
  private RequestMappingHandlerAdapter requestMappingHandlerAdapter;

  private static final Map<Class<?>, Map<String, String>> PARAM_MAPPINGS_CACHE = new ConcurrentHashMap<>(256);

  public ParamNameProcessor() {
    super(false);
  }

  @Override
  public boolean supportsParameter(MethodParameter parameter) {
    return parameter.hasParameterAnnotation(RequestParam.class)
        && !BeanUtils.isSimpleProperty(parameter.getParameterType())
        && Arrays.stream(parameter.getParameterType().getDeclaredFields())
        .anyMatch(field -> field.getAnnotation(ParamName.class) != null);
  }

  @Override
  protected void bindRequestParameters(WebDataBinder binder, NativeWebRequest nativeWebRequest) {
    Object target = binder.getTarget();
    Map<String, String> paramMappings = this.getParamMappings(target.getClass());
    ParamNameDataBinder paramNameDataBinder = new ParamNameDataBinder(target, binder.getObjectName(), paramMappings);
    requestMappingHandlerAdapter.getWebBindingInitializer().initBinder(paramNameDataBinder, nativeWebRequest);
    super.bindRequestParameters(paramNameDataBinder, nativeWebRequest);
  }

  /**
   * Get param mappings.
   * Cache param mappings in memory.
   *
   * @param targetClass
   * @return {@link Map<String, String>}
   */
  private Map<String, String> getParamMappings(Class<?> targetClass) {
    if (PARAM_MAPPINGS_CACHE.containsKey(targetClass)) {
      return PARAM_MAPPINGS_CACHE.get(targetClass);
    }
    Field[] fields = targetClass.getDeclaredFields();
    Map<String, String> paramMappings = new HashMap<>(32);
    for (Field field : fields) {
      ParamName paramName = field.getAnnotation(ParamName.class);
      if (paramName != null && !paramName.value().isEmpty()) {
        paramMappings.put(paramName.value(), field.getName());
      }
    }
    PARAM_MAPPINGS_CACHE.put(targetClass, paramMappings);
    return paramMappings;
  }

}

Finally, a bean configuration for adding ParamNameProcessor into the first of argument resolvers:

@Configuration
public class WebConfig {

  /**
   * Processor for annotation {@link ParamName}.
   *
   * @return ParamNameProcessor
   */
  @Bean
  protected ParamNameProcessor paramNameProcessor() {
    return new ParamNameProcessor();
  }

  /**
   * Custom {@link BeanPostProcessor} for adding {@link ParamNameProcessor} into the first of
   * {@link RequestMappingHandlerAdapter#argumentResolvers}.
   *
   * @return BeanPostProcessor
   */
  @Bean
  public BeanPostProcessor beanPostProcessor() {
    return new BeanPostProcessor() {

      @Override
      public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        return bean;
      }

      @Override
      public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        if (bean instanceof RequestMappingHandlerAdapter) {
          RequestMappingHandlerAdapter adapter = (RequestMappingHandlerAdapter) bean;
          List<HandlerMethodArgumentResolver> argumentResolvers = new ArrayList<>(adapter.getArgumentResolvers());
          argumentResolvers.add(0, paramNameProcessor());
          adapter.setArgumentResolvers(argumentResolvers);
        }
        return bean;
      }
    };
  }

}

Param pojo:

@Data
public class Foo {

  private Integer id;

  @ParamName("first_name")
  private String firstName;

  @ParamName("last_name")
  private String lastName;

  @ParamName("created_at")
  @DateTimeFormat(pattern = "yyyy-MM-dd")
  private Date createdAt;

}

Controller method:

@GetMapping("/foos")
public ResponseEntity<List<Foo>> listFoos(@RequestParam Foo foo, @PageableDefault(sort = "id") Pageable pageable) {
  List<Foo> foos = fooService.listFoos(foo, pageable);
  return ResponseEntity.ok(foos);
}

That's all.

Solution 5:

There is a simple way, you can just add one more setter method, like "setLoc,setJt".