package com.atlassian.plugins.rest.common.validation;
   
   import com.atlassian.plugins.rest.common.interceptor.MethodInvocation;
   import com.atlassian.plugins.rest.common.interceptor.ResourceInterceptor;
   import com.atlassian.sal.api.message.I18nResolver;
   import com.sun.jersey.api.model.AbstractResourceMethod;
   import com.sun.jersey.api.model.Parameter;
   
   import javax.validation.Configuration;
  import javax.validation.ConstraintViolation;
  import javax.validation.MessageInterpolator;
  import javax.validation.Validation;
  import javax.validation.Validator;
  import javax.validation.ValidatorFactory;
  import javax.ws.rs.core.Response;
  import java.lang.reflect.InvocationTargetException;
  import java.util.Set;
  
  /**
   * Uses JSR-303 to validate incoming entity objects.  If validation fails, it will return a 400 with a {@link ValidationErrors}
   * instance containing the constraint violations.  The error messages will be processed with either SAL or the
   * provided custom {@link MessageInterpolator}.
   *
   * @since 2.0
   */
  public class ValidationInterceptor implements ResourceInterceptor {
      private final ValidatorFactory factory;
  
      public ValidationInterceptor(I18nResolver i18nResolver) {
          this(new SalMessageInterpolator(i18nResolver));
  
      }
  
      public ValidationInterceptor(MessageInterpolator messageInterpolator) {
          // Yes, this cast is unnecessary in Java 6, but seems to be required in Java 5
          this.factory = ((Configuration) Validation.byDefaultProvider().configure().messageInterpolator(messageInterpolator)).buildValidatorFactory();
      }
  
      public void intercept(MethodInvocation invocation) throws IllegalAccessException, InvocationTargetException {
          Validator validator = factory.getValidator();
  
          // find the entity for the resource method
          int entityIndex = -1;
          AbstractResourceMethod method = invocation.getMethod();
          for (int i = 0; i < method.getParameters().size(); i++) {
              Parameter parameter = method.getParameters().get(i);
  
              if (Parameter.Source.ENTITY == parameter.getSource()) {
                  entityIndex = i;
                  break;
              }
          }
  
  
          // entity found, so let's validate
          if (entityIndex > -1) {
              Set<ConstraintViolation<Object>> constraintViolations = validator.validate(invocation.getParameters()[entityIndex]);
              if (!constraintViolations.isEmpty()) {
                  ValidationErrors errors = new ValidationErrors();
                  for (ConstraintViolation<Object> violation : constraintViolations) {
                      ValidationError error = new ValidationError();
                      error.setMessage(violation.getMessage());
                      error.setPath(violation.getPropertyPath().toString());
                      errors.addError(error);
                  }
                  invocation.getHttpContext().getResponse().setResponse(Response.status(400).entity(errors).build());
                  return;
              }
          }
  
          invocation.invoke();
      }
  }