content: package com.alibaba.fastjson2.support.spring6.webservlet.view;
  
  import com.alibaba.fastjson2.JSON;
  import com.alibaba.fastjson2.support.config.FastJsonConfig;
  import jakarta.servlet.ServletOutputStream;
  import jakarta.servlet.http.HttpServletRequest;
  import jakarta.servlet.http.HttpServletResponse;
  import org.springframework.http.MediaType;
  import org.springframework.util.CollectionUtils;
  import org.springframework.validation.BindingResult;
  import org.springframework.web.servlet.view.AbstractView;
  
  import java.util.HashMap;
  import java.util.Map;
  import java.util.Set;
  
  /**
   * Fastjson for Spring MVC View.
   *
   * @author Victor.Zxy
   * @see AbstractView
   * @since 2.0.22
   */
  public class FastJsonJsonView
          extends AbstractView {
      /**
       * renderedAttributes
       */
      private Set<String> renderedAttributes;
  
      /**
       * disableCaching
       */
      private boolean disableCaching = true;
  
      /**
       * extractValueFromSingleKeyModel
       */
      private boolean extractValueFromSingleKeyModel;
  
      /**
       * with fastJson config
       */
      private FastJsonConfig config = new FastJsonConfig();
  
      /**
       * Set default param.
       */
      public FastJsonJsonView() {
          setContentType(MediaType.APPLICATION_JSON_VALUE);
          setExposePathVariables(false);
      }
  
      /**
       * @return the fastJsonConfig.
       */
      public FastJsonConfig getFastJsonConfig() {
          return config;
      }
  
      /**
       * @param fastJsonConfig the fastJsonConfig to set.
       */
      public void setFastJsonConfig(FastJsonConfig fastJsonConfig) {
          this.config = fastJsonConfig;
      }
  
      /**
       * Set renderedAttributes.
       *
       * @param renderedAttributes renderedAttributes
       */
      public void setRenderedAttributes(Set<String> renderedAttributes) {
          this.renderedAttributes = renderedAttributes;
      }
  
      /**
       * Check extractValueFromSingleKeyModel.
       *
       * @return extractValueFromSingleKeyModel
       */
      public boolean isExtractValueFromSingleKeyModel() {
          return extractValueFromSingleKeyModel;
      }
  
      /**
       * Set extractValueFromSingleKeyModel.
       */
      public void setExtractValueFromSingleKeyModel(boolean extractValueFromSingleKeyModel) {
          this.extractValueFromSingleKeyModel = extractValueFromSingleKeyModel;
      }
  
      @Override
      protected void renderMergedOutputModel(
              Map<String, Object> model,
              HttpServletRequest request,
              HttpServletResponse response
      ) throws Exception {
          Object value = filterModel(model);
          ServletOutputStream out = response.getOutputStream();
          int len = JSON.writeTo(out, value, config.getDateFormat(), config.getWriterFilters(), config.getWriterFeatures());
          if (config.isWriteContentLength()) {
              // Write content length (determined via byte array).
              response.setContentLength(len);
          }
      }
  
      @Override
      protected void prepareResponse(HttpServletRequest request, //
                                     HttpServletResponse response) {
          setResponseContentType(request, response);
          response.setCharacterEncoding(config.getCharset().name());
          if (this.disableCaching) {
              response.addHeader("Pragma", "no-cache");
              response.addHeader("Cache-Control", "no-cache, no-store, max-age=0");
              response.addDateHeader("Expires", 1L);
          }
      }
  
      /**
       * Disables caching of the generated JSON.
       * <p>
       * Default is {@code true}, which will prevent the client from caching the
       * generated JSON.
       */
      public void setDisableCaching(boolean disableCaching) {
          this.disableCaching = disableCaching;
      }
  
      /**
       * Whether to update the 'Content-Length' header of the response. When set
       * to {@code true}, the response is buffered in order to determine the
       * content length and set the 'Content-Length' header of the response.
       * <p>
       * The default setting is {@code false}.
       */
      public void setUpdateContentLength(boolean updateContentLength) {
          this.config.setWriteContentLength(updateContentLength);
      }
  
      /**
       * 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());
              }
          }
          if (extractValueFromSingleKeyModel) {
              if (result.size() == 1) {
                  for (Map.Entry<String, Object> entry : result.entrySet()) {
                      return entry.getValue();
                  }
              }
          }
          return result;
      }
  
      @Override
      protected void setResponseContentType(HttpServletRequest request, HttpServletResponse response) {
          super.setResponseContentType(request, response);
      }
  }
  