servletutils.java

很好的文件处理程序

// Copyright (C) 1998-2001 by Jason Hunter <jhunter_AT_acm_DOT_org>.
// All rights reserved.  Use of this class is limited.
// Please see the LICENSE for more information.

package com.oreilly.servlet;

import java.io.*;
import java.lang.reflect.*;
import java.net.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.jsp.*;

/** 
 * A collection of static utility methods useful to servlets.
 * Some methods require Servlet API 2.2.
 *
 * @author <b>Jason Hunter</b>, Copyright &#169; 1998-2000
 * @version 1.5, 2001/02/11, added getResource() ".." check
 * @version 1.4, 2000/09/27, finalized getResource() behavior
 * @version 1.3, 2000/08/15, improved getStackTraceAsString() to take Throwable
 * @version 1.2, 2000/03/10, added getResource() method
 * @version 1.1, 2000/02/13, added returnURL() methods
 * @version 1.0, 1098/09/18
 */
public class ServletUtils {

  /**
   * Sends the contents of the specified file to the output stream
   *
   * @param filename the file to send
   * @param out the output stream to write the file
   * @exception FileNotFoundException if the file does not exist
   * @exception IOException if an I/O error occurs
   */
  public static void returnFile(String filename, OutputStream out)
                             throws FileNotFoundException, IOException {
    // A FileInputStream is for bytes
    FileInputStream fis = null;
    try {
      fis = new FileInputStream(filename);
      byte[] buf = new byte[4 * 1024];  // 4K buffer
      int bytesRead;
      while ((bytesRead = fis.read(buf)) != -1) {
        out.write(buf, 0, bytesRead);
      }
    }
    finally {
      if (fis != null) fis.close();
    }
  }

  /**
   * Sends the contents of the specified URL to the output stream
   *
   * @param URL whose contents are to be sent
   * @param out the output stream to write the contents
   * @exception IOException if an I/O error occurs
   */
  public static void returnURL(URL url, OutputStream out) throws IOException {
    InputStream in = url.openStream();
    byte[] buf = new byte[4 * 1024];  // 4K buffer
    int bytesRead;
    while ((bytesRead = in.read(buf)) != -1) {
      out.write(buf, 0, bytesRead);
    }
  }

  /**
   * Sends the contents of the specified URL to the Writer (commonly either a
   * PrintWriter or JspWriter)
   *
   * @param URL whose contents are to be sent
   * @param out the Writer to write the contents
   * @exception IOException if an I/O error occurs
   */
  public static void returnURL(URL url, Writer out) throws IOException {
    // Determine the URL's content encoding
    URLConnection con = url.openConnection();
    con.connect();
    String encoding = con.getContentEncoding();                          

    // Construct a Reader appropriate for that encoding
    BufferedReader in = null;
    if (encoding == null) {
      in = new BufferedReader(
           new InputStreamReader(url.openStream()));
    }
    else {
      in = new BufferedReader(
           new InputStreamReader(url.openStream(), encoding));
    }
    char[] buf = new char[4 * 1024];  // 4Kchar buffer
    int charsRead;
    while ((charsRead = in.read(buf)) != -1) {
      out.write(buf, 0, charsRead);
    }
  }

  /**
   * Gets an exception's stack trace as a String
   *
   * @param e the exception
   * @return the stack trace of the exception
   */
  public static String getStackTraceAsString(Throwable t) {
    ByteArrayOutputStream bytes = new ByteArrayOutputStream();
    PrintWriter writer = new PrintWriter(bytes, true);
    t.printStackTrace(writer);
    return bytes.toString();
  }

  /**
   * Gets a reference to the named servlet, attempting to load it 
   * through an HTTP request if necessary.  Returns null if there's a problem.
   * This method behaves similarly to <tt>ServletContext.getServlet()</tt>
   * except, while that method may return null if the 
   * named servlet wasn't already loaded, this method tries to load 
   * the servlet using a dummy HTTP request.  Only loads HTTP servlets.
   *
   * @param name the name of the servlet
   * @param req the servlet request
   * @param context the servlet context
   * @return the named servlet, or null if there was a problem
   */
  public static Servlet getServlet(String name,
                                   ServletRequest req,
                                   ServletContext context) {
    try {
      // Try getting the servlet the old fashioned way
      Servlet servlet = context.getServlet(name);
      if (servlet != null) return servlet;

      // If getServlet() returned null, we have to load it ourselves.
      // Do this by making an HTTP GET request to the servlet.
      // Use a raw socket connection so we can set a timeout.
      Socket socket = new Socket(req.getServerName(), req.getServerPort());
      socket.setSoTimeout(4000);  // wait up to 4 secs for a response
      PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
      out.println("GET /servlet/" + name + " HTTP/1.0");  // the request
      out.println();
      try {
        socket.getInputStream().read();  // Even one byte means its loaded
      }
      catch (InterruptedIOException e) { /* timeout: ignore, hope for best */ }
      out.close();

      // Try getting the servlet again.
      return context.getServlet(name);
    }
    catch (Exception e) {
      // If there's any problem, return null.
      return null;
    }
  }

  /**
   * Splits a String into pieces according to a delimiter.
   *
   * @param str the string to split
   * @param delim the delimiter
   * @return an array of strings containing the pieces
   */
  public static String[] split(String str, String delim) {
    // Use a Vector to hold the splittee strings
    Vector v = new Vector();

    // Use a StringTokenizer to do the splitting
    StringTokenizer tokenizer = new StringTokenizer(str, delim);
    while (tokenizer.hasMoreTokens()) {
      v.addElement(tokenizer.nextToken());
    }

    String[] ret = new String[v.size()];
    for (int i = 0; i < ret.length; i++) {
      ret[i] = (String) v.elementAt(i);
    }

    return ret;
  }

  /**
   * Gets a reference to the given resource within the given context,
   * making sure not to serve the contents of WEB-INF, META-INF, or to
   * display .jsp file source.
   * Throws an IOException if the resource can't be read.
   *
   * @param context the context containing the resource
   * @param resource the resource to be read
   * @return a URL reference to the resource
   * @exception IOException if there's any problem accessing the resource
   */
  public static URL getResource(ServletContext context, String resource)
                                       throws IOException {
    // Short-circuit if resource is null
    if (resource == null) {
      throw new FileNotFoundException(
        "Requested resource was null (passed in null)");
    }
  
    if (resource.endsWith("/") ||
        resource.endsWith("\\") ||
        resource.endsWith(".")) {
      throw new MalformedURLException("Path may not end with a slash or dot");
    }
  
    if (resource.indexOf("..") != -1) {
      throw new MalformedURLException("Path may not contain double dots");
    }
  
    String upperResource = resource.toUpperCase();
    if (upperResource.startsWith("/WEB-INF") ||
        upperResource.startsWith("/META-INF")) {
      throw new MalformedURLException(
        "Path may not begin with /WEB-INF or /META-INF");
    }
  
    if (upperResource.endsWith(".JSP")) {
      throw new MalformedURLException(
        "Path may not end with .jsp");
    }
  
    // Convert the resource to a URL
    URL url = context.getResource(resource);
    if (url == null) {
      throw new FileNotFoundException(
        "Requested resource was null (" + resource + ")");
    }
  
    return url;
  }
}