Example 7.1 Implementing a Filter – Debugging Filter

public class DebuggingFilter implements Processor {
  private Processor target;

  public DebuggingFilter(Processor myTarget) {
    target = myTarget;
  }

  public void execute(ServletRequest req, 
  ServletResponse res) throws IOException, 
    ServletException 	{
    //Do some filter processing here, such as 
    // displaying request parameters
    target.execute(req, res);
  }
}

Example 7.2 Implementing a Filter – Core Processor

public class CoreProcessor implements Processor {
  private Processor target;
  public CoreProcessor()   {
    this(null);
  }

  public CoreProcessor(Processor myTarget)   {
    target = myTarget;
  }

  public void execute(ServletRequest req, 
      ServletResponse res) throws IOException, 
      ServletException   {
    //Do core processing here
  }
}

Example 7.3 Handling Requests

public void processRequest(ServletRequest req, 
  ServletResponse res) 
  throws IOException, ServletException {
  Processor processors = new DebuggingFilter( 
    new AuthenticationFilter(new CoreProcessor()));
  processors.execute(req, res);

  //Then dispatch to next resource, which is probably 
  // the View to display
  dispatcher.dispatch(req, res);
}

Example 7.4 Messages Written to Standard Output

Debugging filter preprocessing completed...
Authentication filter processing completed...
Core processing completed...
Debugging filter post-processing completed...

Example 7.5 FilterManager – Custom Filter Strategy

public class FilterManager {
  public void processFilter(Filter target, 
    javax.servlet.http.HttpServletRequest request, 
    javax.servlet.http.HttpServletResponse response) 
    throws javax.servlet.ServletException, 
      java.io.IOException 	{                    
    FilterChain filterChain = new FilterChain();

    // The filter manager builds the filter chain here 
    // if necessary

    // Pipe request through Filter Chain
    filterChain.processFilter(request, response);

    //process target resource
    target.execute(request, response);
  }
}

Example 7.6 FilterChain – Custom Filter Strategy

public class FilterChain {
  // filter chain 
  private Vector myFilters = new Vector();

  // Creates new FilterChain 
  public FilterChain() 	{
    // plug-in default filter services for example 
    // only. This would typically be done in the 
    // FilterManager, but is done here for example 
    // purposes
    addFilter(new DebugFilter());
    addFilter(new LoginFilter());
    addFilter(new AuditFilter());
  }

  public void processFilter( 
    javax.servlet.http.HttpServletRequest request,
    javax.servlet.http.HttpServletResponse response)
  throws javax.servlet.ServletException, 
    java.io.IOException 	{
    Filter filter;

    // apply filters
    Iterator filters = myFilters.iterator();
    while (filters.hasNext())
    {
      filter = (Filter)filters.next();
      // pass request & response through various 
      // filters
      filter.execute(request, response);
    }
  }

  public void addFilter(Filter filter) 	{
    myFilters.add(filter);
  }
}

Example 7.7 Base Filter – Standard Filter Strategy

public class BaseEncodeFilter implements 
      javax.servlet.Filter {
  private javax.servlet.FilterConfig myFilterConfig;

  public BaseEncodeFilter()     {  }

  public void doFilter(
    javax.servlet.ServletRequest servletRequest, 
    javax.servlet.ServletResponse servletResponse,
    javax.servlet.FilterChain filterChain) 
  throws java.io.IOException,
    javax.servlet.ServletException {
    filterChain.doFilter(servletRequest, 
        servletResponse);
  }

  public javax.servlet.FilterConfig getFilterConfig() 
  {
    return myFilterConfig; 
  }
    
  public void setFilterConfig(
    javax.servlet.FilterConfig filterConfig) {
      myFilterConfig = filterConfig;
  }
}

Example 7.8 StandardEncodeFilter – Standard Filter Strategy

public class StandardEncodeFilter 
  extends BaseEncodeFilter {
  // Creates new StandardEncodeFilter
  public StandardEncodeFilter()   {  }

  public void doFilter(javax.servlet.ServletRequest 
    servletRequest,javax.servlet.ServletResponse 
    servletResponse,javax.servlet.FilterChain 
    filterChain) 
  throws java.io.IOException, 
    javax.servlet.ServletException {

    String contentType = 
      servletRequest.getContentType();
    if ((contentType == null) || 
      contentType.equalsIgnoreCase(
        "application/x-www-form-urlencoded"))     {
      translateParamsToAttributes(servletRequest, 
        servletResponse);
    }

    filterChain.doFilter(servletRequest, 
      servletResponse);
  }

  private void translateParamsToAttributes(
    ServletRequest request, ServletResponse response)
  {
    Enumeration paramNames = 
        request.getParameterNames();

    while (paramNames.hasMoreElements())     {
      String paramName = (String) 
          paramNames.nextElement();

      String [] values;

      values = request.getParameterValues(paramName);
      System.err.println("paramName = " + paramName);
      if (values.length == 1)
        request.setAttribute(paramName, values[0]);
      else
        request.setAttribute(paramName, values);
    }
 }
}

Example 7.9 MultipartEncodeFilter – Standard Filter Strategy

public class MultipartEncodeFilter extends 
  BaseEncodeFilter {
  public MultipartEncodeFilter() { }
  public void doFilter(javax.servlet.ServletRequest 
    servletRequest, javax.servlet.ServletResponse 
    servletResponse,javax.servlet.FilterChain 
    filterChain)
  throws java.io.IOException, 
    javax.servlet.ServletException {
    String contentType = 
      servletRequest.getContentType();   
    // Only filter this request if it is multipart 
    // encoding                
    if (contentType.startsWith(
                "multipart/form-data")){
      try {
        String uploadFolder = 
          getFilterConfig().getInitParameter(
              "UploadFolder");
        if (uploadFolder == null) uploadFolder = ".";

        /** The MultipartRequest class is: 
        * Copyright (C) 2001 by Jason Hunter 
        * <jhunter@servlets.com>. All rights reserved. 
        **/
        MultipartRequest multi = new 
          MultipartRequest(servletRequest, 
                           uploadFolder,
                           1 * 1024 * 1024 );
        Enumeration params = 
	         multi.getParameterNames();
        while (params.hasMoreElements()) {
          String name = (String)params.nextElement();
          String value = multi.getParameter(name);
          servletRequest.setAttribute(name, value);
        }

        Enumeration files = multi.getFileNames();
        while (files.hasMoreElements()) {
          String name = (String)files.nextElement();
          String filename = multi.getFilesystemName(name);
          String type = multi.getContentType(name);
          File f = multi.getFile(name);
          // At this point, do something with the 
          // file, as necessary
        }
      }
      catch (IOException e)
      {
        LogManager.logMessage(
          "error reading or saving file"+ e);
      }
    } // end if
    filterChain.doFilter(servletRequest, 
                         servletResponse);
  } // end method doFilter()
}

Example 7.10 Deployment Descriptor – Standard Filter Strategy

.
.
.
<filter>
    <filter-name>StandardEncodeFilter</filter-name>
    <display-name>StandardEncodeFilter</display-name>
    <description></description>
    <filter-class> corepatterns.filters.encodefilter.
            StandardEncodeFilter</filter-class>
  </filter>
  <filter>
    <filter-name>MultipartEncodeFilter</filter-name>
    <display-name>MultipartEncodeFilter</display-name>
    <description></description>
    <filter-class>corepatterns.filters.encodefilter.
            MultipartEncodeFilter</filter-class>
    <init-param>
      <param-name>UploadFolder</param-name>
      <param-value>/home/files</param-value>
    </init-param>
 </filter>
.
.
.
<filter-mapping>
    <filter-name>StandardEncodeFilter</filter-name>
    <url-pattern>/EncodeTestServlet</url-pattern>
  </filter-mapping>
  <filter-mapping>
    <filter-name>MultipartEncodeFilter</filter-name>
    <url-pattern>/EncodeTestServlet</url-pattern>
  </filter-mapping>
.
.
.

Example 7.11 Base Filter Strategy

public class BaseEncodeFilter implements 
  javax.servlet.Filter {
  private javax.servlet.FilterConfig myFilterConfig;
	
  public BaseEncodeFilter() 		{	}

  public void doFilter(javax.servlet.ServletRequest 	
    servletRequest,javax.servlet.ServletResponse 
    servletResponse, javax.servlet.FilterChain 
    filterChain) throws java.io.IOException, 
    javax.servlet.ServletException {

    filterChain.doFilter(servletRequest, 
      servletResponse);
  }

  public javax.servlet.FilterConfig getFilterConfig() {
    return myFilterConfig; 
  }
    
  public void 
  setFilterConfig(javax.servlet.FilterConfig 
    filterConfig) {
    myFilterConfig = filterConfig;
  }
}

Example 7.12 Using a Template Filter Strategy

public abstract class TemplateFilter implements 
  javax.servlet.Filter {
  private FilterConfig filterConfig;

  public void setFilterConfig(FilterConfig fc) { 
    filterConfig=fc; 
  }

  public FilterConfig getFilterConfig() 	{ 
    return filterConfig; 
  }

  public void doFilter(ServletRequest request, 
    ServletResponse response, FilterChain chain)
    throws IOException, ServletException {
    // Common processing for all filters can go here 
    doPreProcessing(request, response, chain);

    // Common processing for all filters can go here
    doMainProcessing(request, response, chain);

    // Common processing for all filters can go here 
    doPostProcessing(request, response, chain);

    // Common processing for all filters can go here

    // Pass control to the next filter in the chain or 
    // to the target resource
    chain.doFilter(request, response);
  }
  public void doPreProcessing(ServletRequest request, 	
    ServletResponse response, FilterChain chain) {
  }

  public void doPostProcessing(ServletRequest request, 
    ServletResponse response, FilterChain chain) {
  }

  public abstract void doMainProcessing(ServletRequest 
   request, ServletResponse response, FilterChain 
   chain);
}