httpmessage.java

java高级使用教程 全书一共分六章

package chat;

import java.io.*;
import java.net.*;
import java.util.*;

/** A class to simplify HTTP applet-server communication.  It abstracts
 *  the communication into messages, which can be either GET or POST.
 */
public class HttpMessage {

  URL servlet = null;
  Hashtable headers = null;

  public HttpMessage(URL servlet) {
    this.servlet = servlet;
  }

  public InputStream sendGetMessage() throws IOException {
    return sendGetMessage(null);
  }

  /**
   * Performs a GET request to the servlet, building
   * a query string from the supplied properties list.
   */
  public InputStream sendGetMessage(Properties args) throws IOException {
    String argString = "";  // default

    if (args != null) {
      argString = "?" + toEncodedString(args);
    }
    URL url = new URL(servlet.toExternalForm() + argString); 

    // Turn off caching
    URLConnection con = url.openConnection();
    con.setUseCaches(false);

    sendHeaders(con);

    return con.getInputStream();
  }

  /** Performs a POST request to the servlet, with no query string.
   */
  public InputStream sendPostMessage() throws IOException {
    return sendPostMessage(null);
  }

  /** Performs a POST request to the servlet, building
   * post data from the supplied properties list.
   */
  public InputStream sendPostMessage(Properties args) throws IOException {
    String argString = "";  // default
    if (args != null) {
      argString = toEncodedString(args);  // notice no "?"
    }

    URLConnection con = servlet.openConnection();
System.out.println("HttpMessage");
    // Prepare for both input and output
    con.setDoInput(true);
    con.setDoOutput(true);

    // Turn off caching
    con.setUseCaches(false);

    // Work around a Netscape bug
    con.setRequestProperty(
        "Content-Type", "application/x-www-form-urlencoded");

    sendHeaders(con);

    // Write the arguments as post data
    DataOutputStream out = new DataOutputStream(con.getOutputStream());
    out.writeBytes(argString);
    out.flush();
    out.close();

    return con.getInputStream();
  }

  /* Performs a POST request to the servlet, uploading a serialized object.
   */
  public InputStream sendPostMessage(Serializable obj) throws IOException {
    URLConnection con = servlet.openConnection();

    con.setDoInput(true);
    con.setDoOutput(true);
    con.setUseCaches(false);

    con.setRequestProperty(
        "Content-Type", "application/x-java-serialized-object");
        
    sendHeaders(con);

    // Write the serialized object as post data
    ObjectOutputStream out = new ObjectOutputStream(con.getOutputStream());
    out.writeObject(obj);
    out.flush();
    out.close();

    return con.getInputStream();
  }

  /* Sets a request header with the given name and value.  The header 
   * persists across multiple requests.  The caller is responsible for
   * ensuring there are no illegal characters in the name and value.
   */
  public void setHeader(String name, String value) {
    if (headers == null) {
      headers = new Hashtable();
    }
    headers.put(name, value);
  }

  // Send the contents of the headers hashtable to the server
  private void sendHeaders(URLConnection con) {
    if (headers != null) {
      Enumeration enum = headers.keys();
      while (enum.hasMoreElements()) {
        String name = (String) enum.nextElement();
        String value = (String) headers.get(name);
        con.setRequestProperty(name, value);
      }
    }
  }

 /** Sets a request cookie with the given name and value.  The cookie 
   * persists across multiple requests.  The caller is responsible for
   * ensuring there are no illegal characters in the name and value.
   */
  public void setCookie(String name, String value) {
    if (headers == null) {
      headers = new Hashtable();
    }
    String existingCookies = (String) headers.get("Cookie");
    if (existingCookies == null) {
      setHeader("Cookie", name + "=" + value);
    }
    else {
      setHeader("Cookie", existingCookies + "; " + name + "=" + value);
    }
  }

 /** Sets the authorization information for the request (using BASIC
   * authentication via the HTTP Authorization header).  The authorization 
   * persists across multiple requests.
   
  public void setAuthorization(String name, String password) {
    String authorization = Base64Encoder.encode(name + ":" + password);
    setHeader("Authorization", "Basic " + authorization);
  }
*/
  /* Converts a properties list to a URL-encoded query string */ 
  private String toEncodedString(Properties args) {
    StringBuffer buf = new StringBuffer();
    Enumeration names = args.propertyNames();
    while (names.hasMoreElements()) {
      String name = (String) names.nextElement();
      String value = args.getProperty(name);
      buf.append(URLEncoder.encode(name) + "=" + URLEncoder.encode(value));
      if (names.hasMoreElements()) buf.append("&");
    }
    return buf.toString();
  }
}