www.pudn.com > j2mewireless_examples.zip > NetworkQuery.java

/*
 * Copyright (c) 2000-2001 Sun Microsystems, Inc. All Rights Reserved.
 */

package examples.addressbook;
import java.io.*;
import java.util.*;
import javax.microedition.rms.*;
import javax.microedition.io.*;

/*
 * Class to query a network service for address book entries
 * and parse the result. Uses HttpConnection to fetch
 * the entries from a server.
 *
 * The http request is made using a base url provided by the caller
 * with the query arguments for last name and first name
 * encoded in the query parameters of the URL.
 */
public class NetworkQuery implements RecordEnumeration {
    private StringBuffer buffer = new StringBuffer(60);
    private String[] fields = new String[3];
    private String empty = new String();
    private Vector results = new Vector(20);
    private Enumeration resultsEnumeration;

    final static String baseurl =
        "http://127.0.0.1:8080/Book/netaddr";

    /**
     * Create a RecordEnumeration from the network.
     *
     * Query a network service for addresses matching the
     * specified criteria. The base URL of the service
     * has the query parameters appended. The request is
     * made and the contents parsed into a Vector which
     * is used as the basis of the RecordEnumeration.
     * lastname  the last name to search for
     * firstname the first name to search for
     * sortorder the order in which to sort
     *       1 is by last name, 0 is by first name
     */
    NetworkQuery(String firstname,
                 String lastname,
                 int sortorder) {
        HttpConnection c = null;
        int ch;
        InputStream is = null;
        InputStreamReader reader;
        String url;

        // Format the complete URL to request
        buffer.setLength(0);
        buffer.append(baseurl);
        buffer.append("?last=");
        buffer.append((lastname != null) ? lastname : empty);
        buffer.append("&first=");
        buffer.append((firstname != null) ? firstname : empty);
        buffer.append("&sort=" + sortorder);

        url = buffer.toString();

        // Open the connection to the service
        try {
            c = open(url);
            results.removeAllElements();

            /*
             * Open the InputStream and construct a reader to
             * convert from bytes to chars.
             */
            is = c.openInputStream();
            reader = new InputStreamReader(is);
            while (true) {
                int i = 0;
                fields[0] = empty;
                fields[1] = empty;
                fields[2] = empty;
                do {
                    buffer.setLength(0);
                    while ((ch = reader.read()) != -1 &&
                        (ch != ',') && (ch != '\n')) {
                        if (ch == '\r') {
                            continue;
                        }
                        buffer.append((char)ch);
                    }

                    if (ch == -1) {
                        throw new EOFException();
                    }

                    if (buffer.length() > 0) {
                        if (i < fields.length) {
                            fields[i++] = buffer.toString();
                        }
                    }
                } while (ch != '\n');

                if (fields[0].length() > 0) {
                    results.addElement(
                        SimpleRecord.createRecord(
                            fields[0], fields[1], fields[2]));
                }
            }
        } catch (Exception e) {

        } finally {
            try {
                if (is != null) {
                    is.close();
                }
                if (c != null) {
                    c.close();
                }
            } catch (Exception e) {
            }
        }
        resultsEnumeration = results.elements();
    }

    /**
     * Read the HTTP headers and the data using HttpConnection.
     * Check the response code to ensure successful open.
     * 
     * Connector.open is used to open url and a HttpConnection
     * is returned.
     * The HTTP headers are read and processed.
     *  url the URL to open
     * throws IOException for any network related exception
     */
    private HttpConnection open(String url) throws IOException {
        HttpConnection c;
        int status = -1;

        // Open the connection and check for redirects
        while (true) {
            c = (HttpConnection)Connector.open(url);

            // Get the status code, 
            // causing the connection to be made
            status = c.getResponseCode();

            if ((status == HttpConnection.HTTP_TEMP_REDIRECT) ||
                (status == HttpConnection.HTTP_MOVED_TEMP) ||
                (status == HttpConnection.HTTP_MOVED_PERM)) {

                // Get the new location and close the connection
                url = c.getHeaderField("location");
                c.close();
            } else {
                break;
            }
        }

        // Only HTTP_OK (200) means the content is returned.
        if (status != HttpConnection.HTTP_OK) {
            c.close();
            throw new IOException("Response status not OK");
        }
        return c;
    }

    /**
     * Returns true if more elements exist in enumeration.
     */
    public boolean hasNextElement() {
        return resultsEnumeration.hasMoreElements();
    }

    /**
     * Returns a copy of the next record in this enumeration,
     */
    public byte[] nextRecord() {
        return (byte[])resultsEnumeration.nextElement();
    }

    /**
     * The following are simply stubs that we don't
     * implement...
     */
    public boolean hasPreviousElement() {return false;}
    public void destroy() {}
    public boolean isKeptUpdated() {return false;}
    public void keepUpdated(boolean b) {return;}
    public int nextRecordId() {return 0;}
    public int numRecords() {return 0;}
    public byte[] previousRecord() {return null;}
    public int previousRecordId() {return 0;}
    public void rebuild() {return;}
    public void reset() {return;}
}