ServletUtils


1   // Copyright (C) 1998-2001 by Jason Hunter <jhunter_AT_acm_DOT_org>.
2   // All rights reserved.  Use of this class is limited.
3   // Please see the LICENSE for more information.
4   
5   package com.oreilly.servlet;
6   
7   import java.io.*;
8   import java.lang.reflect.*;
9   import java.net.*;
10  import java.util.*;
11  import javax.servlet.*;
12  import javax.servlet.http.*;
13  //import javax.servlet.jsp.*;
14  
15  /**
16   * A collection of static utility methods useful to servlets.
17   * Some methods require Servlet API 2.2.
18   *
19   * @author <b>Jason Hunter</b>, Copyright &#169; 1998-2000
20   * @version 1.5, 2001/02/11, added getResource() ".." check
21   * @version 1.4, 2000/09/27, finalized getResource() behavior
22   * @version 1.3, 2000/08/15, improved getStackTraceAsString() to take Throwable
23   * @version 1.2, 2000/03/10, added getResource() method
24   * @version 1.1, 2000/02/13, added returnURL() methods
25   * @version 1.0, 1098/09/18
26   */
27  public class ServletUtils {
28  
29    /**
30     * Sends the contents of the specified file to the output stream
31     *
32     * @param filename the file to send
33     * @param out the output stream to write the file
34     * @exception FileNotFoundException if the file does not exist
35     * @exception IOException if an I/O error occurs
36     */
37    public static void returnFile(String   filename, OutputStream out)
38                               throws FileNotFoundException, IOException {
39      // A FileInputStream is for bytes
40      FileInputStream fis = null;
41      try {
42        fis = new FileInputStream(filename);
43        byte[] buf = new byte[4 * 1024];  // 4K buffer
44        int bytesRead;
45        while ((bytesRead = fis.read(buf)) != -1) {
46          out.write(buf, 0, bytesRead);
47        }
48      }
49      finally {
50        if (fis != null) fis.close();
51      }
52    }
53  
54    /**
55     * Sends the contents of the specified URL to the output stream
56     *
57     * @param URL whose contents are to be sent
58     * @param out the output stream to write the contents
59     * @exception IOException if an I/O error occurs
60     */
61    public static void returnURL(URL url, OutputStream out) throws IOException {
62      InputStream in = url.openStream();
63      byte[] buf = new byte[4 * 1024];  // 4K buffer
64      int bytesRead;
65      while ((bytesRead = in.read(buf)) != -1) {
66        out.write(buf, 0, bytesRead);
67      }
68    }
69  
70    /**
71     * Sends the contents of the specified URL to the Writer (commonly either a
72     * PrintWriter or JspWriter)
73     *
74     * @param URL whose contents are to be sent
75     * @param out the Writer to write the contents
76     * @exception IOException if an I/O error occurs
77     */
78    public static void returnURL(URL url, Writer out) throws IOException {
79      // Determine the URL's content encoding
80      URLConnection con = url.openConnection();
81      con.connect();
82      String   encoding = con.getContentEncoding();
83  
84      // Construct a Reader appropriate for that encoding
85      BufferedReader in = null;
86      if (encoding == null) {
87        in = new BufferedReader(
88             new InputStreamReader(url.openStream()));
89      }
90      else {
91        in = new BufferedReader(
92             new InputStreamReader(url.openStream(), encoding));
93      }
94      char[] buf = new char[4 * 1024];  // 4Kchar buffer
95      int charsRead;
96      while ((charsRead = in.read(buf)) != -1) {
97        out.write(buf, 0, charsRead);
98      }
99    }
100 
101   /**
102    * Gets an exception's stack trace as a String
103    *
104    * @param e the exception
105    * @return the stack trace of the exception
106    */
107   public static String   getStackTraceAsString(Throwable   t) {
108     ByteArrayOutputStream bytes = new ByteArrayOutputStream();
109     PrintWriter writer = new PrintWriter(bytes, true);
110     t.printStackTrace(writer);
111     return bytes.toString();
112   }
113 
114   /**
115    * Gets a reference to the named servlet, attempting to load it
116    * through an HTTP request if necessary.  Returns null if there's a problem.
117    * This method behaves similarly to <tt>ServletContext.getServlet()</tt>
118    * except, while that method may return null if the
119    * named servlet wasn't already loaded, this method tries to load
120    * the servlet using a dummy HTTP request.  Only loads HTTP servlets.
121    *
122    * @param name the name of the servlet
123    * @param req the servlet request
124    * @param context the servlet context
125    * @return the named servlet, or null if there was a problem
126    */
127   public static Servlet getServlet(String   name,
128                                    ServletRequest req,
129                                    ServletContext context) {
130     try {
131       // Try getting the servlet the old fashioned way
132       Servlet servlet = context.getServlet(name);
133       if (servlet != null) return servlet;
134 
135       // If getServlet() returned null, we have to load it ourselves.
136       // Do this by making an HTTP GET request to the servlet.
137       // Use a raw socket connection so we can set a timeout.
138       Socket socket = new Socket(req.getServerName(), req.getServerPort());
139       socket.setSoTimeout(4000);  // wait up to 4 secs for a response
140       PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
141       out.println("GET /servlet/" + name + " HTTP/1.0");  // the request
142       out.println();
143       try {
144         socket.getInputStream().read();  // Even one byte means its loaded
145       }
146       catch (InterruptedIOException e) { /* timeout: ignore, hope for best */ }
147       out.close();
148 
149       // Try getting the servlet again.
150       return context.getServlet(name);
151     }
152     catch (Exception   e) {
153       // If there's any problem, return null.
154       return null;
155     }
156   }
157 
158   /**
159    * Gets a reference to the given resource within the given context,
160    * making sure not to serve the contents of WEB-INF, META-INF, or to
161    * display .jsp file source.
162    * Throws an IOException if the resource can't be read.
163    *
164    * @param context the context containing the resource
165    * @param resource the resource to be read
166    * @return a URL reference to the resource
167    * @exception IOException if there's any problem accessing the resource
168    */
169   public static URL getResource(ServletContext context, String   resource)
170                                        throws IOException {
171     // Short-circuit if resource is null
172     if (resource == null) {
173       throw new FileNotFoundException(
174         "Requested resource was null (passed in null)");
175     }
176 
177     if (resource.endsWith("/") ||
178         resource.endsWith("\\") ||
179         resource.endsWith(".")) {
180       throw new MalformedURLException("Path may not end with a slash or dot");
181     }
182 
183     if (resource.indexOf("..") != -1) {
184       throw new MalformedURLException("Path may not contain double dots");
185     }
186 
187     String   upperResource = resource.toUpperCase();
188     if (upperResource.startsWith("/WEB-INF") ||
189         upperResource.startsWith("/META-INF")) {
190       throw new MalformedURLException(
191         "Path may not begin with /WEB-INF or /META-INF");
192     }
193 
194     if (upperResource.endsWith(".JSP")) {
195       throw new MalformedURLException(
196         "Path may not end with .jsp");
197     }
198 
199     // Convert the resource to a URL
200     URL url = context.getResource(resource);
201     if (url == null) {
202       throw new FileNotFoundException(
203         "Requested resource was null (" + resource + ")");
204     }
205 
206     return url;
207   }
208 }
209
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