EmptyView.java

/**
 * Licensed to Apereo under one or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information regarding copyright ownership. Apereo
 * licenses this file to you under the Apache License, Version 2.0 (the "License"); you may not use
 * this file except in compliance with the License. You may obtain a copy of the License at the
 * following location:
 *
 * <p>http://www.apache.org/licenses/LICENSE-2.0
 *
 * <p>Unless required by applicable law or agreed to in writing, software distributed under the
 * License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
 * express or implied. See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.jasig.portlet.calendar.mvc;

import java.util.HashMap;
import java.util.Map;
import java.util.Set;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.codehaus.jackson.JsonEncoding;
import org.codehaus.jackson.JsonGenerator;
import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.map.SerializerFactory;
import org.springframework.util.Assert;
import org.springframework.util.CollectionUtils;
import org.springframework.validation.BindingResult;
import org.springframework.web.servlet.view.AbstractView;

public class EmptyView extends AbstractView {

  public EmptyView() {
    setContentType(DEFAULT_CONTENT_TYPE);
  }

  /** Default content type. Overridable as bean property. */
  public static final String DEFAULT_CONTENT_TYPE = "application/json";

  private ObjectMapper objectMapper = new ObjectMapper();

  private JsonEncoding encoding = JsonEncoding.UTF8;

  private boolean prefixJson = false;

  private Set<String> renderedAttributes;

  /**
   * Sets the {@code ObjectMapper} for this view. If not set, a default {@link
   * ObjectMapper#ObjectMapper() ObjectMapper} is used.
   *
   * <p>Setting a custom-configured {@code ObjectMapper} is one way to take further control of the
   * JSON serialization process. For example, an extended {@link SerializerFactory} can be
   * configured that provides custom serializers for specific types. The other option for refining
   * the serialization process is to use Jackson's provided annotations on the types to be
   * serialized, in which case a custom-configured ObjectMapper is unnecessary.
   */
  public void setObjectMapper(ObjectMapper objectMapper) {
    Assert.notNull(objectMapper, "'objectMapper' must not be null");
    this.objectMapper = objectMapper;
  }

  /**
   * Sets the {@code JsonEncoding} for this converter. By default, {@linkplain JsonEncoding#UTF8
   * UTF-8} is used.
   */
  public void setEncoding(JsonEncoding encoding) {
    Assert.notNull(encoding, "'encoding' must not be null");
    this.encoding = encoding;
  }

  /**
   * Indicates whether the JSON output by this view should be prefixed with "{@code {} &&}". Default
   * is false.
   *
   * <p>Prefixing the JSON string in this manner is used to help prevent JSON Hijacking. The prefix
   * renders the string syntactically invalid as a script so that it cannot be hijacked. This prefix
   * does not affect the evaluation of JSON, but if JSON validation is performed on the string, the
   * prefix would need to be ignored.
   */
  public void setPrefixJson(boolean prefixJson) {
    this.prefixJson = prefixJson;
  }

  /**
   * Sets the attributes in the model that should be rendered by this view. When set, all other
   * model attributes will be ignored.
   */
  public void setRenderedAttributes(Set<String> renderedAttributes) {
    this.renderedAttributes = renderedAttributes;
  }

  @Override
  protected void prepareResponse(HttpServletRequest request, HttpServletResponse response) {
    response.setContentType(getContentType());
    response.setCharacterEncoding(encoding.getJavaName());
  }

  @Override
  protected void renderMergedOutputModel(
      Map<String, Object> model, HttpServletRequest request, HttpServletResponse response)
      throws Exception {
    JsonGenerator generator =
        objectMapper.getJsonFactory().createJsonGenerator(response.getOutputStream(), encoding);
    generator.writeRaw("    ");
  }

  /**
   * Filters out undesired attributes from the given model. The return value can be either another
   * {@link Map}, or a single value object.
   *
   * <p>Default implementation removes {@link BindingResult} instances and entries not included in
   * the {@link #setRenderedAttributes(Set) renderedAttributes} property.
   *
   * @param model the model, as passed on to {@link #renderMergedOutputModel}
   * @return the object to be rendered
   */
  protected Object filterModel(Map<String, Object> model) {
    Map<String, Object> result = new HashMap<String, Object>(model.size());
    Set<String> renderedAttributes =
        !CollectionUtils.isEmpty(this.renderedAttributes)
            ? this.renderedAttributes
            : model.keySet();
    for (Map.Entry<String, Object> entry : model.entrySet()) {
      if (!(entry.getValue() instanceof BindingResult)
          && renderedAttributes.contains(entry.getKey())) {
        result.put(entry.getKey(), entry.getValue());
      }
    }
    return result;
  }
}