checkpassword.java

21天学通java的示例程序源代码

/*
 * CheckPassword.java
 */
package com.wrox.password;

import java.io.*;
import java.net.*;
import java.security.*;

/**
 * Checks passwords from an unencrypted password file. For demonstration
 * purposes only - this is not production quality code!
 */
public class CheckPassword {

  /**
   * Checks a password. This method uses a doPrivileged block, so there
   * is no need for the caller to have permission to read the password
   * file.
   * @param username The user to check the password for
   * @param password The password
   * @param passwordLocation The password file URL to use when checking
   * @return <code>true</code> if the password is correct
   */
  public boolean check(final String username, final String password, 
                       final String passwordLocation) {

    // First verify that the callers have permission to check passwords
    SecurityManager security = System.getSecurityManager();
    if (security != null) {
      security.checkPermission(new CheckPasswordPermission());
    } 

    // Then check the password in a privileged code block
    Boolean passwordOk = 
      (Boolean) AccessController.doPrivileged(new PrivilegedAction() {
      public Object run() {

        // start of privileged code
        try {
          boolean ok = privilegedCheck(username, password, 
                                       passwordLocation);
          return new Boolean(ok);
        } catch (IOException e) {
          return Boolean.FALSE;
        } 

        // end of privileged code
      } 
    });

    return passwordOk.booleanValue();
  } 

  /**
   * Checks a password. The caller needs to have permission to read the
   * password file.
   * @param username The user to check the password for
   * @param password The password
   * @param passwordLocation The password file URL to use when checking
   * @return <code>true</code> if the password is correct
   * @throws IOException if the password URL could not be read
   */
  public boolean privilegedCheck(String username, String password, 
                                 String passwordLocation) throws IOException {
    String toSearch = username + ":";
    String passwordFound = null;
    URL passwordUrl = new URL(passwordLocation);
    BufferedReader passwords = 
      new BufferedReader(new InputStreamReader(passwordUrl.openStream()));

    try {
      while (true) {
        String line = passwords.readLine();
        if (line == null) {
          break;

        } 
        if (line.startsWith(toSearch)) {
          passwordFound = line.substring(toSearch.length());
          break;
        } 
      } 
    } 
    finally {
      passwords.close();
    } 
    return passwordFound != null && password.equals(passwordFound);
  } 
}