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17.4 A Query Viewer That Uses Object Serialization and HTTP Tunneling

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Listing 17.5 QueryCollection.java 

import java.net.*;

import java.io.*;

/** When this class is built, it returns a value

 *  immediately, but this value returns false for isDone

 *  and null for getQueries. Meanwhile, it starts a Thread

 *  to request an array of query strings from the server,

 *  reading them in one fell swoop by means of an

 *  ObjectInputStream. Once they've all arrived, they

 *  are placed in the location getQueries returns,

 *  and the isDone flag is switched to true.

 *  Used by the ShowQueries applet.

 */

public class QueryCollection implements Runnable {

  private String[] queries;

  private String[] tempQueries;

  private boolean isDone = false;

  private URL dataURL;

  public QueryCollection(String urlSuffix, URL currentPage) {

    try {

      // Only the URL suffix need be supplied, since

      // the rest of the URL is derived from the current page.

      String protocol = currentPage.getProtocol();

      String host = currentPage.getHost();

      int port = currentPage.getPort();

      dataURL = new URL(protocol, host, port, urlSuffix);

      Thread queryRetriever = new Thread(this);

      queryRetriever.start();

    } catch(MalformedURLException mfe) {

      isDone = true;

    }

  }

  public void run() {

    try {

      tempQueries = retrieveQueries();

      queries = tempQueries;

    } catch(IOException ioe) {

      tempQueries = null;

      queries = null;

    }

    isDone = true;

  }

  public String[] getQueries() {

    return(queries);

  }

  public boolean isDone() {

    return(isDone);

  }

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