Metacat

/**

 *  '$RCSfile$'

 *    Purpose: A Class that implements replication for metacat

 *  Copyright: 2000 Regents of the University of California and the

 *             National Center for Ecological Analysis and Synthesis

 *    Authors: Chad Berkley

 *    Release: @release@

 *

 *   '$Author: bojilova $'

 *     '$Date: 2001-09-24 10:55:00 -0700 (Mon, 24 Sep 2001) $'

 * '$Revision: 840 $'

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License as published by

 * the Free Software Foundation; either version 2 of the License, or

 * (at your option) any later version.

 *

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, write to the Free Software

 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

 */

package edu.ucsb.nceas.metacat;

import java.util.*;

import java.io.*;

import java.sql.*;

import java.net.*;

import java.lang.*;

import java.text.*;

import javax.servlet.*;

import javax.servlet.http.*;

import org.xml.sax.*;

public class MetacatReplication extends HttpServlet implements Runnable

{  

  private String deltaT;

  Timer replicationDaemon;

  private static MetaCatUtil util = new MetaCatUtil();

  private Vector fileLocks = new Vector();

  private Thread lockThread = null;

  /**

   * Initialize the servlet by creating appropriate database connections

   */

  public void init(ServletConfig config) throws ServletException 

  {

    //initialize db connections to handle any update requests

    MetaCatUtil util = new MetaCatUtil();

    deltaT = util.getOption("deltaT");

    //the default deltaT can be set from metacat.properties

    //create a thread to do the delta-T check but don't execute it yet

    replicationDaemon = new Timer(true);

  }

  public void destroy() 

  {

    replicationDaemon.cancel();

   // System.out.println("Replication daemon cancelled.");

  }

  public void doGet (HttpServletRequest request, HttpServletResponse response)

                     throws ServletException, IOException 

  {

    // Process the data and send back the response

    handleGetOrPost(request, response);

  }

  public void doPost(HttpServletRequest request, HttpServletResponse response)

                     throws ServletException, IOException 

  {

    // Process the data and send back the response

    handleGetOrPost(request, response);

  }

  private void handleGetOrPost(HttpServletRequest request, 

                               HttpServletResponse response) 

                               throws ServletException, IOException 

  {

    PrintWriter out = response.getWriter();

    Hashtable params = new Hashtable();

    Enumeration paramlist = request.getParameterNames(); 

// NOT NEEDED - doesn't provide enough security because of possible IP spoofing

// REPLACED with running replication comminications over HTTPS

//    String requestingServerIP = request.getRemoteAddr();

//    InetAddress iaddr = InetAddress.getByName(requestingServerIP);

//    String requestingServer = iaddr.getHostName();

    while (paramlist.hasMoreElements()) {

      String name = (String)paramlist.nextElement();

      String[] value = request.getParameterValues(name);

      params.put(name, value);  

    }

    String action = ((String[])params.get("action"))[0];

    String server = null;

    try {

      // check if the server is included in the list of replicated servers

      if ( !action.equals("servercontrol") && 

           !action.equals("stop") &&

           !action.equals("start") &&

           !action.equals("getall") ) {

        server = ((String[])params.get("server"))[0];

        if ( getServerCode(server) == 0 ) {

          System.out.println("Action \"" + action + 

                             "\" rejected for server: " + server);

          return;

        } else {

          System.out.println("Action \"" + action + 

                             "\" accepted for server: " + server);

        }

      }

    } catch (Exception e) {

      System.out.println("Error in MetacatReplication.handleGetOrPost: " +

                         e.getMessage() );

      return;

    }

    if ( action.equals("stop") ) {

      //stop the replication server

      replicationDaemon.cancel();

      replicationDaemon = new Timer(true);

      out.println("Replication Handler Stopped");

      MetacatReplication.replLog("deltaT handler stopped");

    } else if ( action.equals("start") ) {

      //start the replication server

      int rate;

      if ( params.containsKey("rate") ) {

        rate = new Integer(

               new String(((String[])params.get("rate"))[0])).intValue();

        if(rate < 30) {

            out.println("Replication deltaT rate cannot be less than 30!");

            //deltaT<30 is a timing mess!

            rate = 1000;

        }

      } else {

        rate = 1000;

      }

      out.println("New rate is: " + rate + " seconds.");

      replicationDaemon.cancel();

      replicationDaemon = new Timer(true);

      replicationDaemon.scheduleAtFixedRate(new ReplicationHandler(out), 0, 

                                            rate * 1000);

      out.println("Replication Handler Started");

      MetacatReplication.replLog("deltaT handler started with rate=" + 

                                    rate + " seconds");

    } else if ( action.equals("getall") ) {

      //updates this server exactly once

      replicationDaemon.schedule(new ReplicationHandler(out), 0);

      response.setContentType("text/html");

      out.println("<html><body>\"Get All\" Done</body></html>");

    } else if ( action.equals("forcereplicate") ) {

      handleForceReplicateRequest(out, params, response);

    } else if ( action.equals("update") ) {

      //request an update list from the server

      handleUpdateRequest(out, params, response);

    } else if ( action.equals("read") ) {

      //request a specific document from the server

      //note that this could be replaced by a call to metacatServlet

      //handleGetDocumentAction().

      handleGetDocumentRequest(out, params, response);

    } else if ( action.equals("getlock") ) {

      handleGetLockRequest(out, params, response);

    } else if ( action.equals("getdocumentinfo") ) {

      handleGetDocumentInfoRequest(out, params, response);

    } else if ( action.equals("gettime") ) {

      handleGetTimeRequest(out, params, response);

    } else if ( action.equals("getcatalog") ) {

      handleGetCatalogRequest(out, params, response, true);

    } else if ( action.equals("servercontrol") ) {

      handleServerControlRequest(out, params, response);

    }

    out.close();

  }

  /** 

   * This method can add, delete and list the servers currently included in

   * xml_replication.

   * action           subaction            other needed params

   * ---------------------------------------------------------

   * servercontrol    add                  server

   * servercontrol    delete               server

   * servercontrol    list                 

   */

  private void handleServerControlRequest(PrintWriter out, Hashtable params,

                                          HttpServletResponse response)

  {

    String subaction = ((String[])params.get("subaction"))[0];

    Connection conn = null;

    try {

      conn = util.openDBConnection();

      PreparedStatement pstmt = null;

      // add server to server list

      if ( subaction.equals("add") ) {

        String replicate = ((String[])params.get("replicate"))[0];

        String server = ((String[])params.get("server"))[0];

        pstmt = conn.prepareStatement("INSERT INTO xml_replication " +

                                      "(server, last_checked, replicate) " +

                                      "VALUES ('" + server + "', to_date(" +

                                      "'01/01/00', 'MM/DD/YY'), '" +

                                      replicate + "')");

        pstmt.execute();

        pstmt.close();

        conn.commit();

        out.println("Server " + server + " added"); 

        response.setContentType("text/html");

        out.println("<html><body><table border=\"1\">");

        out.println("<tr><td><b>server</b></td><td><b>last_checked</b></td><td>");

        out.println("<b>replicate</b></td></tr>");

        pstmt = conn.prepareStatement("SELECT * FROM xml_replication");

        pstmt.execute();

        ResultSet rs = pstmt.getResultSet();

        boolean tablehasrows = rs.next();

        while(tablehasrows) {

          out.println("<tr><td>" + rs.getString(2) + "</td><td>");

          out.println(rs.getString(3) + "</td><td>");

          out.println(rs.getString(4) + "</td></tr>");

          tablehasrows = rs.next();

        }

        out.println("</table></body></html>");

        // download certificate with the public key on this server

        // and import it as a trusted certificate

        String certURL = ((String[])params.get("certificate"))[0];

        downloadCertificate(certURL);

      // delete server from server list

      } else if ( subaction.equals("delete") ) {

        String server = ((String[])params.get("server"))[0];

        pstmt = conn.prepareStatement("DELETE FROM xml_replication " +

                                      "WHERE server LIKE '" + server + "'");

        pstmt.execute();

        pstmt.close();

        conn.commit();

        out.println("Server " + server + " deleted");

        response.setContentType("text/html");

        out.println("<html><body><table border=\"1\">");

        out.println("<tr><td><b>server</b></td><td><b>last_checked</b></td><td>");

        out.println("<b>replicate</b></td></tr>");

        pstmt = conn.prepareStatement("SELECT * FROM xml_replication");

        pstmt.execute();

        ResultSet rs = pstmt.getResultSet();

        boolean tablehasrows = rs.next();

        while(tablehasrows)

        {

          out.println("<tr><td>" + rs.getString(2) + "</td><td>");

          out.println(rs.getString(3) + "</td><td>");

          out.println(rs.getString(4) + "</td></tr>");

          tablehasrows = rs.next();

        }

        out.println("</table></body></html>");

      // list servers in server list

      } else if ( subaction.equals("list") ) {

        response.setContentType("text/html");

        out.println("<html><body><table border=\"1\">");

        out.println("<tr><td><b>server</b></td><td><b>last_checked</b></td><td>");

        out.println("<b>replicate</b></td></tr>");

        pstmt = conn.prepareStatement("SELECT * FROM xml_replication");

        pstmt.execute();

        ResultSet rs = pstmt.getResultSet();

        boolean tablehasrows = rs.next();

        while(tablehasrows) {

          out.println("<tr><td>" + rs.getString(2) + "</td><td>");

          out.println(rs.getString(3) + "</td><td>");

          out.println(rs.getString(4) + "</td></tr>");

          tablehasrows = rs.next();

        }

        out.println("</table></body></html>");

      }

      pstmt.close();

      conn.close();

    } catch(Exception e) {

      System.out.println("Error in " + 

                         "MetacatReplication.handleServerControlRequest " + 

                         e.getMessage());

      e.printStackTrace(System.out);

    }

  }

  // download certificate with the public key from certURL and 

  // upload it onto this server; it then must be imported as a 

  // trusted certificate 

  private void downloadCertificate (String certURL)

                throws FileNotFoundException, IOException, MalformedURLException

  {

    MetaCatUtil util = new MetaCatUtil();

    String certPath = util.getOption("certPath"); //the path to be uploaded to

    // get filename from the URL of the certificate

    String filename = certURL;

    int slash = Math.max(filename.lastIndexOf('/'), filename.lastIndexOf('\\'));

    if ( slash > -1 ) {

      filename = filename.substring(slash + 1);

    }

    // open file output strem to write the input into it

    File f = new File(certPath, filename);

    synchronized (f) { 

      try {

        if ( f.exists() ) {

          throw new IOException("File already exist: " + f.getCanonicalFile());

          //if ( f.exists() && !f.canWrite() ) {

          //  throw new IOException("Not writable: " + f.getCanonicalFile());

        }

      } catch (SecurityException se) {

        // if a security manager exists,

        // its checkRead method is called for f.exist()

        // or checkWrite method is called for f.canWrite()

        throw se;

      }

      // create a buffered byte output stream

      // that uses a default-sized output buffer

      FileOutputStream fos = new FileOutputStream(f);

      BufferedOutputStream out = new BufferedOutputStream(fos);

      // this should be http url

      URL url = new URL(certURL);

      BufferedInputStream bis = null;

      try {

        bis = new BufferedInputStream(url.openStream());

        byte[] buf = new byte[4 * 1024]; // 4K buffer

        int b = bis.read(buf);

        while (b != -1) {

          out.write(buf, 0, b);

          b = bis.read(buf);

        }

      } finally {

        if (bis != null) bis.close();

      }

      // the input and the output streams must be closed

      bis.close();

	    out.flush();

	    out.close();

	    fos.close();

    } // end of synchronized(f)

  }

  /**

   * when a forcereplication request comes in, this method sends a read request

   * to the requesting server for the specified docid.

   */

  private void handleForceReplicateRequest(PrintWriter out, Hashtable params,

                                           HttpServletResponse response)

  {

    String server = ((String[])params.get("server"))[0]; // the server that

    String docid = ((String[])params.get("docid"))[0]; // sent the document

    String dbaction = "UPDATE"; // the default action is UPDATE

    boolean override = false;

    int serverCode = 1;

    try {

      //if the url contains a dbaction then the default action is overridden

      if(params.containsKey("dbaction")) {

        dbaction = ((String[])params.get("dbaction"))[0];

        serverCode = MetacatReplication.getServerCode(server);

        override = true; //we are now overriding the default action

      }

      MetacatReplication.replLog("force replication request from " + server); 

      // sending back read request to server

      URL u = new URL("https://" + server + "?action=read&docid=" + docid);

      String xmldoc = MetacatReplication.getURLContent(u);

      // get the document info from server

      URL docinfourl = new URL("https://" + server + 

                               "?action=getdocumentinfo&docid=" + docid);

      String docInfoStr = MetacatReplication.getURLContent(docinfourl);

      //dih is the parser for the docinfo xml format

      DocInfoHandler dih = new DocInfoHandler();

      XMLReader docinfoParser = ReplicationHandler.initParser(dih);

      docinfoParser.parse(new InputSource(new StringReader(docInfoStr)));

      Hashtable docinfoHash = dih.getDocInfo();

      String user = (String)docinfoHash.get("user_owner");

      // write the document here

System.out.println("Open db connection");

      Connection conn = util.openDBConnection();

System.out.println("DB connection opened");

      DocumentImpl.write(conn, new StringReader(xmldoc), null, dbaction, docid, 

                         user, null, serverCode, override);

      conn.close();

      MetacatReplication.replLog("document " + docid + " added to DB with " +

                                 "action " + dbaction);

    } catch(Exception e) {

      System.out.println("ERROR in MetacatReplication.handleForceReplicate" +

                         "Request(): " + e.getMessage());

    }

  }

  /**

   * Grants or denies a lock to a requesting host.

   * The servlet parameters of interrest are:

   * docid: the docid of the file the lock is being requested for

   * currentdate: the timestamp of the document on the remote server

   * 

   */

  private void handleGetLockRequest(PrintWriter out, Hashtable params,

                                    HttpServletResponse response)

  {

    Connection conn = null;

    try

    {

      conn = MetacatReplication.getDBConnection("MetacatReplication." +

                                                "handleGetLockRequest");

      String docid = ((String[])params.get("docid"))[0];

      String remoteRev = ((String[])params.get("updaterev"))[0];

      DocumentImpl requestDoc = new DocumentImpl(conn, docid);

      MetacatReplication.replLog("lock request for " + docid);

      int localRevInt = requestDoc.getRev();

      int remoteRevInt = Integer.parseInt(remoteRev);

      if(remoteRevInt >= localRevInt)

      {

        if(!fileLocks.contains(docid))

        { //grant the lock if it is not already locked

          fileLocks.add(0, docid); //insert at the beginning of the queue Vector

          //send a message back to the the remote host authorizing the insert

          out.println("<lockgranted><docid>" +docid+ "</docid></lockgranted>");

          lockThread = new Thread(this);

          lockThread.setPriority(Thread.MIN_PRIORITY);

          lockThread.start();

          System.out.println("lock granted for " + docid);

          MetacatReplication.replLog("lock granted for " + docid);

        }

        else

        { //deny the lock

          out.println("<filelocked><docid>" + docid + "</docid></filelocked>");

          MetacatReplication.replLog("lock denied for " + docid + 

                                     "reason: file already locked");

        }

      }

      else

      {//deny the lock.

        out.println("<outdatedfile><docid>" + docid + "</docid></filelocked>");

        MetacatReplication.replLog("lock denied for " + docid + 

                                   "reason: client has outdated file");

      }

      conn.close();

    }

    catch(Exception e)

    {

      System.out.println("error requesting file lock from MetacatReplication." +

                         "handleGetLockRequest: " + e.getMessage());

      e.printStackTrace(System.out);

    }

  }

  /**

   * Sends all of the xml_documents information encoded in xml to a requestor

   * the format is:

   * <!ELEMENT documentinfo (docid, docname, doctype, doctitle, user_owner,

   *                         user_updated, public_access, rev)

   * all of the subelements of document info are #PCDATA

   */

  private void handleGetDocumentInfoRequest(PrintWriter out, Hashtable params, 

                                        HttpServletResponse response)

  {

    String docid = ((String[])(params.get("docid")))[0];

    StringBuffer sb = new StringBuffer();

    Connection conn = null;

    try

    {

      conn = MetacatReplication.getDBConnection("MetacatReplication." +

                                                "handleGetDocumentInfoRequest");

      DocumentImpl doc = new DocumentImpl(conn, docid);

      sb.append("<documentinfo><docid>").append(docid);

      sb.append("</docid><docname>").append(doc.getDocname());

      sb.append("</docname><doctype>").append(doc.getDoctype());

      sb.append("</doctype>");

// DOCTITLE attr cleared from the db

//      sb.append("</doctype><doctitle>").append(doc.getDocTitle());

      sb.append("<user_owner>").append(doc.getUserowner());

      sb.append("</user_owner><user_updated>").append(doc.getUserupdated());

      sb.append("</user_updated><public_access>").append(doc.getPublicaccess());

      sb.append("</public_access><rev>").append(doc.getRev());

      sb.append("</rev></documentinfo>");

      response.setContentType("text/xml");

      out.println(sb.toString());

      conn.close();

    }

    catch (Exception e)

    {

      System.out.println("error in " +

                         "metacatReplication.handlegetdocumentinforequest: " + 

                          e.getMessage());

    }

  }

  /**

   * Sends a document to a remote host

   */

  private void handleGetDocumentRequest(PrintWriter out, Hashtable params, 

                                        HttpServletResponse response)

  {

    Connection conn = null;

    try

    {

      String docid = ((String[])(params.get("docid")))[0];

      System.out.println("incoming get request for document: " + docid);

      conn = MetacatReplication.getDBConnection("MetacatReplication." +

                                                "handleGetDocumentRequest");

      DocumentImpl di = new DocumentImpl(conn, docid);

      response.setContentType("text/xml");

      out.print(di.toString());

      conn.close();

      MetacatReplication.replLog("document " + docid + " sent");

      System.out.println("document " + docid + " sent");

    }

    catch(Exception e)

    {

      System.out.println("error getting document from MetacatReplication." +

                         "handlGetDocumentRequest " + e.getMessage());

      e.printStackTrace(System.out);

    }

  }

  /**

   * Sends a list of all of the documents on this sever along with their

   * revision numbers.  

   * The format is:

   * <!ELEMENT replication (server, updates)>

   * <!ELEMENT server (#PCDATA)>

   * <!ELEMENT updates ((updatedDocument | deleteDocument)*)>

   * <!ELEMENT updatedDocument (docid, rev)>

   * <!ELEMENT deletedDocument (docid, rev)>

   * <!ELEMENT docid (#PCDATA)>

   * <!ELEMENT rev (#PCDATA)>

   * note that the rev in deletedDocument is always empty.  I just left

   * it in there to make the parser implementation easier.

   */

  private void handleUpdateRequest(PrintWriter out, Hashtable params, 

                                    HttpServletResponse response)

  {

    Connection conn = null;

    try

    {

      System.out.println("received update request");

      StringBuffer docsql = new StringBuffer();

      StringBuffer doclist = new StringBuffer();

      Vector packageFiles = new Vector();

      //get all docs that reside on this server

      doclist.append("<?xml version=\"1.0\"?><replication>");

      doclist.append("<server>").append(util.getOption("server"));

      doclist.append(util.getOption("replicationpath"));

      doclist.append("</server><updates>");

      docsql.append("select docid, rev, doctype from xml_documents where "); 

      docsql.append("server_location = 1");

      //get any deleted documents

      StringBuffer delsql = new StringBuffer();

      delsql.append("select distinct docid from ");

      delsql.append("xml_revisions where docid not in (select docid from ");

      delsql.append("xml_documents) and server_location = 1");

      conn = MetacatReplication.getDBConnection("MetacatReplication." +

                                                "handleUpdateRequest");

      PreparedStatement pstmt = conn.prepareStatement(docsql.toString());

      pstmt.execute();

      ResultSet rs = pstmt.getResultSet();

      boolean tablehasrows = rs.next();

      while(tablehasrows)

      {

        String recordDoctype = rs.getString(3);

        if(!recordDoctype.equals("BIN"))

        { //don't replicate data files

          if(!recordDoctype.equals(util.getOption("packagedoctype")))

          { //if this is a package file, put it at the end

            //because if a package file is read before all of the files it

            //refers to are loaded then there is an error

            doclist.append("<updatedDocument>");

            doclist.append("<docid>").append(rs.getString(1));

            doclist.append("</docid><rev>").append(rs.getInt(2));

            doclist.append("</rev>");

            doclist.append("</updatedDocument>");

          }

          else

          { //the package files are saved to be put into the xml later.

            Vector v = new Vector();

            v.add(new String(rs.getString(1)));

            v.add(new Integer(rs.getInt(2)));

            packageFiles.add(new Vector(v));

          }

        }

        tablehasrows = rs.next();

      }

      pstmt = conn.prepareStatement(delsql.toString());

      pstmt.execute();

      rs = pstmt.getResultSet();

      tablehasrows = rs.next();

      while(tablehasrows)

      { //handle the deleted documents

        doclist.append("<deletedDocument><docid>").append(rs.getString(1));

        doclist.append("</docid><rev></rev></deletedDocument>");

        //note that rev is always empty for deleted docs

        tablehasrows = rs.next();

      }

      //now we can put the package files into the xml results

      for(int i=0; i<packageFiles.size(); i++)

      {

        Vector v = (Vector)packageFiles.elementAt(i);

        doclist.append("<updatedDocument>");

        doclist.append("<docid>").append((String)v.elementAt(0));

        doclist.append("</docid><rev>");

        doclist.append(((Integer)v.elementAt(1)).intValue());

        doclist.append("</rev>");

        doclist.append("</updatedDocument>");

      }

      doclist.append("</updates></replication>");

      MetaCatUtil.debugMessage("doclist: " + doclist.toString());

      pstmt.close();

      conn.close();

      response.setContentType("text/xml");

      out.println(doclist.toString());

      System.out.println("doclist: " + doclist.toString());

      System.out.println("update request handled");

    }

    catch(Exception e)

    {

      System.out.println("error in MetacatReplication.handleupdaterequest: " + 

                          e.getMessage());

      e.printStackTrace(System.out);

    }

  }

  /**

   * Returns the xml_catalog table encoded in xml

   */

  public static String getCatalogXML()

  {

    return handleGetCatalogRequest(null, null, null, false);

  }

  /**

   * Sends the contents of the xml_catalog table encoded in xml

   * The xml format is:

   * <!ELEMENT xml_catalog (row*)>

   * <!ELEMENT row (entry_type, source_doctype, target_doctype, public_id,

   *                system_id)>

   * All of the sub elements of row are #PCDATA

   * If printFlag == false then do not print to out.

   */

  private static String handleGetCatalogRequest(PrintWriter out, 

                                                Hashtable params,

                                                HttpServletResponse response,

                                                boolean printFlag)

  {

    Connection conn = null;

    PreparedStatement pstmt = null;

    try

    { 

      conn = MetacatReplication.getDBConnection("MetacatReplication." +

                                                "handleGetCatalogRequest");

      pstmt = conn.prepareStatement("select entry_type, " +

                              "source_doctype, target_doctype, public_id, " +

                              "system_id from xml_catalog");

      pstmt.execute();

      ResultSet rs = pstmt.getResultSet();

      boolean tablehasrows = rs.next();

      StringBuffer sb = new StringBuffer();

      sb.append("<?xml version=\"1.0\"?><xml_catalog>");

      while(tablehasrows)

      {

        sb.append("<row><entry_type>").append(rs.getString(1));

        sb.append("</entry_type><source_doctype>").append(rs.getString(2));

        sb.append("</source_doctype><target_doctype>").append(rs.getString(3));

        sb.append("</target_doctype><public_id>").append(rs.getString(4));

        sb.append("</public_id><system_id>").append(rs.getString(5));

        sb.append("</system_id></row>");

        tablehasrows = rs.next();

      }

      sb.append("</xml_catalog>");

      conn.close();

      if(printFlag)

      {

        response.setContentType("text/xml");

        out.println(sb.toString());

      }

      pstmt.close();

      return sb.toString();

    }

    catch(Exception e)

    {

      try

      {

        pstmt.close();

        conn.close();

      }

      catch(Exception ee)

      {}

      System.out.println("error in MetacatReplication.handleGetCatalogRequest:"+ 

                          e.getMessage());

      e.printStackTrace(System.out);

    }

    return null;

  }

  /**

   * Sends the current system date to the remote server.  Using this action

   * for replication gets rid of any problems with syncronizing clocks 

   * because a time specific to a document is always kept on its home server.

   */

  private void handleGetTimeRequest(PrintWriter out, Hashtable params, 

                                    HttpServletResponse response)

  {

    SimpleDateFormat formatter = new SimpleDateFormat ("yy-MM-dd HH:mm:ss");

    java.util.Date localtime = new java.util.Date();

    String dateString = formatter.format(localtime);

    response.setContentType("text/xml");

    out.println("<timestamp>" + dateString + "</timestamp>");

  }

  /**

   * this method handles the timeout for a file lock.  when a lock is 

   * granted it is granted for 30 seconds.  When this thread runs out

   * it deletes the docid from the queue, thus eliminating the lock.

   */

  public void run()

  {

    try

    {

      MetaCatUtil.debugMessage("thread started for docid: " + 

                               (String)fileLocks.elementAt(0));

      System.out.println("thread started for docid: " + 

                               (String)fileLocks.elementAt(0));

      Thread.sleep(30000); //the lock will expire in 30 seconds

      MetaCatUtil.debugMessage("thread for docid: " + 

                             (String)fileLocks.elementAt(fileLocks.size() - 1) + 

                              " exiting.");

      System.out.println("thread for docid: " + 

                         (String)fileLocks.elementAt(fileLocks.size() - 1) + 

                         " exiting.");

      fileLocks.remove(fileLocks.size() - 1);

      //fileLocks is treated as a FIFO queue.  If there are more than one lock

      //in the vector, the first one inserted will be removed.

    }

    catch(Exception e)

    {

      System.out.println("error in file lock thread from MetacatReplication." + 

                         "run: " + e.getMessage());

    }

  }

  /**

   * Returns the name of a server given a serverCode

   * @param serverCode the serverid of the server

   * @return the servername or null if the specified serverCode does not

   *         exist.

   */

  public static String getServer(int serverCode)

  {

    //System.out.println("serverid: " + serverCode);

    Connection conn = null;

    try

    {

      conn = MetacatReplication.getDBConnection("MetacatReplication." +

                                                "getServer");

      String sql = new String("select server from " +

                              "xml_replication where serverid = " + 

                              serverCode);

      PreparedStatement pstmt = conn.prepareStatement(sql);

      //System.out.println("getserver sql: " + sql);

      pstmt.execute();

      ResultSet rs = pstmt.getResultSet();

      boolean tablehasrows = rs.next();

      if(tablehasrows)

      {

        //System.out.println("server: " + rs.getString(1));

        return rs.getString(1);

      }

      pstmt.close();

      conn.close();

    }

    catch(Exception e)

    {

      System.out.println("Error in MetacatReplication.getServer: " + 

                          e.getMessage());

    }

    return null;

      //return null if the server does not exist

  }

  /**

   * Returns a server code given a server name

   * @param server the name of the server

   * @return integer > 0 representing the code of the server, 0 if the server

   *  does not exist.

   */

  public static int getServerCode(String server) throws Exception

  {

    Connection conn = null;

    PreparedStatement pstmt = null;

    int serverCode = 0;

    try {

      conn = util.openDBConnection();