Metacat

/**

 *  '$RCSfile$'

 *    Purpose: A Class that creates an XML text document

 *             from a query to a relational DB containing a DOM representation

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

 *             National Center for Ecological Analysis and Synthesis

 *    Authors: Matt Jones

 *    Release: @release@

 *

 *   '$Author: jones $'

 *     '$Date: 2000-08-14 13:53:34 -0700 (Mon, 14 Aug 2000) $'

 * '$Revision: 349 $'

 */

package edu.ucsb.nceas.metacat;

import java.io.*;

import java.sql.*;

/** 

 * A Class that creates an XML text document

 * from a query to a relational DB containing a DOM representation

 */

public class DBReader {

  private Connection	conn = null;

  /**

   * main routine used for testing.

   * <p>

   * Usage: java DBReader <docid>

   *

   * @param nodeid the id number of the root of the subtree to display

   */

  static public void main(String[] args) {

     if (args.length < 1)

     {

        System.err.println("Wrong number of arguments!!!");

        System.err.println("USAGE: java DBReader <docid>");

        return;

     } else {

        try {

          String docid = args[0];

          // Open a connection to the database

          MetaCatUtil   util = new MetaCatUtil();

          Connection dbconn = util.openDBConnection();

          DBReader rd = new DBReader( dbconn );

          String xml = rd.readXMLDocument(docid);

          System.out.println(xml);

        } catch (McdbException me) {

          me.toXml(new PrintWriter(System.err));

        } catch (Exception e) {

          System.err.println("EXCEPTION HANDLING REQUIRED");

          System.err.println(e.getMessage());

          e.printStackTrace(System.err);

        }

     }

  }

  /**

   * construct a DBReader instance.

   *

   * Generally, one calls readXMLDocument() after constructing the instance

   *

   * @param conn the database connection from which to read the document

   */

  public DBReader( Connection conn ) 

  {

    this.conn = conn;

  }

  /**

   * Get the root node id for an XML document given a document id

   *

   * @param docid the document node contains the root of the document

   * @returns long the nodeid of the root node for this document

   */

  private long getRootNode(String docid) 

          throws McdbDocNotFoundException

  {

    // Now look up the root node id

    long rootnodeid = 0;

    try {

      PreparedStatement pstmt =

        conn.prepareStatement("SELECT rootnodeid " +

                "FROM xml_documents " +

                "WHERE docid = ?");

      // Bind the values to the query

      pstmt.setString(1, docid);

      pstmt.execute();

        ResultSet rs = pstmt.getResultSet();

          boolean tableHasRows = rs.next();

          if (tableHasRows) {

              rootnodeid = rs.getLong(1);

          }

      pstmt.close();

    } catch (SQLException e) {

      throw new McdbDocNotFoundException(

                "Root node not found for: " + docid, e);

    }

    return rootnodeid;

  }

  /**

   * Create an XML document from the database starting with the element 

   * having element_id nodeid

   *

   * @param docid the document that we want retrieved

   */

  public String readXMLDocument(String docid) 

         throws McdbException

  {

    try {

      StringBuffer doc = new StringBuffer();

      DoctypeInfo dti = getDoctypeInfo(docid);

      String docname = dti.getDocname();

      String doctype = dti.getDoctype();

      String sysid = dti.getSystemID();

      ElementNode element = new ElementNode(conn, getRootNode(docid));

      doc.append("<?xml version=\"1.0\"?>\n");

      if (docname != null) {

        if ((doctype != null) && (sysid != null)) {

          doc.append("<!DOCTYPE " + docname + " PUBLIC \"" + doctype + 

                     "\" \"" + sysid + "\">\n");

        } else {

          doc.append("<!DOCTYPE " + docname + ">\n");

        }

      }

      doc.append(element.toString());

      return (doc.toString());

    } catch (McdbException ex) {

      throw ex;

    } catch (Throwable t) {

      throw new McdbException("Error reading document " + docid + ".");

    }

  }

  /**

   * Look up the document type information from the database

   *

   * @param docid the id of the document to look up

   */

  public DoctypeInfo getDoctypeInfo(String docid) 

    throws McdbException 

  {

    PreparedStatement pstmt;

    String doctype = null;

    String docname = null;

    String sysid   = null;

    DoctypeInfo dti = null;

    try {

      pstmt =

        conn.prepareStatement("SELECT docname,doctype " +

                                "FROM xml_documents " +

                               "WHERE docid = ?");

      // Bind the values to the query

      pstmt.setString(1, docid);

      pstmt.execute();

      ResultSet rs = pstmt.getResultSet();

      boolean tableHasRows = rs.next();

      if (tableHasRows) {

        docname  = rs.getString(1);

        doctype  = rs.getString(2);

      } 

      pstmt.close();

      if (doctype != null) {

        pstmt =

          conn.prepareStatement("SELECT system_id " +

                                  "FROM xml_catalog " +

                                 "WHERE public_id = ?");

        // Bind the values to the query

        pstmt.setString(1, doctype);

        pstmt.execute();

        rs = pstmt.getResultSet();

        tableHasRows = rs.next();

        if (tableHasRows) {

          sysid  = rs.getString(1);

        } 

        pstmt.close();

      }

    } catch (SQLException e) {

      throw new McdbException("Error accessing database connection.", e);

    }

    if (docname != null) {

      dti = new DoctypeInfo(docname, doctype, sysid);

      return dti;

    } else {

      throw new McdbDocNotFoundException("Document not found: " + docid);

    }

  }

  /**

   * A utility class that encapsulates document type information

   */

  public class DoctypeInfo {

    private String docname = null;

    private String doctype = null;

    private String system_id = null;

    /**

     * Constructor

     */

    public DoctypeInfo(String docname, String doctype, String system_id) {

      this.docname = docname;

      this.doctype = doctype;

      this.system_id = system_id;

    }

    /**

     * get the document name

     */

    public String getDocname() {

      return docname;

    }

    /**

     * get the document type

     */

    public String getDoctype() {

      return doctype;

    }

    /**

     * get the system identifier

     */

    public String getSystemID() {

      return system_id;

    }

  }

}

/**

 * '$Log$

 * 'Revision 1.19  2000/08/11 22:20:04  jones

 * 'Changed exception handling mechanisms for DBReader

 * '

 * 'Revision 1.18  2000/08/10 22:39:04  jones

 * 'changed getRootNode method from public to private

 * '

 * 'Revision 1.17  2000/06/26 10:35:05  jones

 * 'Merged in substantial changes to DBWriter and associated classes and to

 * 'the MetaCatServlet in order to accomodate the new UPDATE and DELETE

 * 'functions.  The command line tools and the parameters for the

 * 'servlet have changed substantially.

 * '

 * 'Revision 1.16.2.2  2000/06/25 23:38:16  jones

 * 'Added RCSfile keyword

 * '

 * 'Revision 1.16.2.1  2000/06/25 23:34:17  jones

 * 'Changed documentation formatting, added log entries at bottom of source files

 * ''

 */