Metacat

/**

 *      Name: DBReader.java

 *   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

 *

 *   Version: '$Id: DBReader.java 184 2000-06-21 02:57:19Z jones $'

 */

package edu.ucsb.nceas.metacat;

import java.io.*;

import java.net.URL;

import java.net.MalformedURLException;

import java.sql.*;

import java.util.Stack;

/** 

 * 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 (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 ) 

                  throws IOException, 

                         SQLException, 

                         ClassNotFoundException

  {

    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

   */

  public long getRootNode(String docid) {

    // 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();

      try {

        ResultSet rs = pstmt.getResultSet();

        try {

          boolean tableHasRows = rs.next();

          if (tableHasRows) {

            try {

              rootnodeid = rs.getLong(1);

            } catch (SQLException e) {

              System.out.println("Error with getLong: " + e.getMessage());

            }

          }

        } catch (SQLException e) {

          System.out.println("Error with next: " + e.getMessage());

        }

      } catch (SQLException e) {

        System.out.println("Error with getrset: " + e.getMessage());

      }

      pstmt.close();

    } catch (SQLException e) {

      System.out.println("Error getting id: " + e.getMessage());

    }

    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) {

    StringBuffer doc = new StringBuffer();

    DoctypeInfo dti = getDoctypeInfo(docid);

    if (dti != null) {

      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());

    } else {

      doc.append("<error>Document " + docid + " not found.</error>");

    }

    return (doc.toString());

  }

  /**

   * Look up the document type information from the database

   *

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

   */

  public DoctypeInfo getDoctypeInfo(String docid) {

    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) {

      System.out.println("Error getting id: " + e.getMessage());

    }

    if (docname != null) {

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

    } else {

      dti = null;

    }

    return dti;

  }

  /**

   * 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;

    }

  }

}