exceptionmanager.java

ORACLE AQ sample 演示的如何出列

package oracle.otnsamples.AQ.Manager;

/**
 * @author  Rajat Gupta
 * @version 1.0
 *
 * Name of the Application        :  ExceptionManager.java
 * Development Environment        :  Oracle 9i JDeveloper
 * Creation/Modification History  :
 *
 *    Rajat Gupta       15-Jan-2001      Created
 *
 */

// Servlet Imports
import javax.servlet.http.HttpServletRequest;

// Util Imports
import java.util.Hashtable;

// Net  Imports
import java.net.URL;

// W3C Imports
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.w3c.dom.NamedNodeMap;

import org.xml.sax.SAXException;

// Oracle XML Imports
import oracle.xml.parser.v2.DOMParser;
import oracle.xml.parser.v2.XMLDocument;
import oracle.xml.parser.v2.XMLParser;
import oracle.xml.parser.v2.XMLParseException;

// IO Imports
import java.io.IOException;

// Oracle XML Schema Imports
import oracle.xml.parser.schema.XSDBuilder;
import oracle.xml.parser.schema.XMLSchema;

// Other files
import oracle.otnsamples.AQ.Helper.CreateURL;

/**
 * This is the main class that handles all the exceptions occurring in the
 * sample. All the exceptions generated in the sample will throw a new
 * exception with some ID which will be propagated to this class. This
 * class parses a XML file Exceptions.xml which has the String to be
 * displayed for each ID. If an exception is thrown which is not caught
 * by the sample, then a default error message will be shown to the user.
 * @see Manager.java
 */
public class ExceptionManager implements Manager{
  /**
   * This is a Hashtable which stores the exception ID and the String
   * to be displayed for that ID. This Hashtable is populated by parsing
   * the Exceptions.xml
   */
  private final Hashtable m_exceptionTable;

  /**
   * This constructor creates the URL to the Exceptions.xml and
   * parses it.
   *
   * @exception Exception If an unreported exception is thrown
   * @see CreateURL.java
   */
  public ExceptionManager() throws Exception{
    CreateURL createURL = new CreateURL();
    URL xmlURL = createURL.getURL("AQConfig/Exceptions.xml");
    URL schemaURL = createURL.getURL("AQConfig/Exception.xsd");

    m_exceptionTable = parseXML(xmlURL, schemaURL);
  }

  /**
   * This is the main method that does the actual parsing of the XML file.
   * It stores the exception ID and its value in a Hashtable which is
   * returned.
   *
   * @exception Exception If an unreported exception is thrown
   * @param p_url URL to Exceptions.xml
   * @return Exception Hashtable
   */
  static Hashtable parseXML(URL p_xmlURL, URL p_schemaURL) throws Exception{
    Hashtable exceptionParameters = new Hashtable();
    try{

      // Define the variables used for parsing
      Node childNode, node;
      NodeList nodeList;
      NamedNodeMap nnm;

      // Get an instance of the parser
      DOMParser parser = new DOMParser();
      XSDBuilder builder = new XSDBuilder();

      XMLSchema schemadoc = (XMLSchema)builder.build(p_schemaURL);
      parser.setXMLSchema(schemadoc);

      // Set various parser options: validation on,
      // warnings shown, error stream set to stderr.
      parser.setErrorStream(System.err);

      // This statement will be used when we write the schema for the XML file
      parser.setValidationMode(XMLParser.SCHEMA_VALIDATION);

      parser.showWarnings(true);

      // Parse the document.
      parser.parse(p_xmlURL);

      // Obtain the document.
      XMLDocument doc = parser.getDocument();

      // Get all the Child Nodes in a NodeList
      nodeList = doc.getFirstChild().getNextSibling().getNextSibling().getChildNodes();

      // Iterate through the nodelist and get the Attribute and value of
      // DataSource used to connect to the DataBase. Store these then in
      // the Hashtable.
      for (int j=0; j<nodeList.getLength() ; j++){
        childNode = nodeList.item(j);
        nnm = childNode.getAttributes();
        node = nnm.item(0);

        exceptionParameters.put(node.getNodeValue(),
                           childNode.getFirstChild().getFirstChild().getNodeValue());
      }
      return exceptionParameters;
    }
    catch(XMLParseException p_xmlexp){
      p_xmlexp.printStackTrace();
      throw new Exception("AQ-1017");
    }catch(IOException p_ioexp){
      p_ioexp.printStackTrace();
      throw new Exception("AQ-1005");
    }
    catch(SAXException p_saxexp){
      p_saxexp.printStackTrace();
      throw new Exception("AQ-1008");
    }
    catch(Exception p_exp){
      throw p_exp;
    }
  }

  /**
   * This method is called if any exception occurs in the application.
   * It gets the corresponding message to be displayed for the ID from the
   * Hashtable. If the ID is not present, then a default ID is assigned.
   *
   * @param p_request HttpServlet Request Object
   * @param p_exception Exception thrown
   * @exception Exception If an unreported exception is thrown
   */
  public void getException(HttpServletRequest p_request, Exception p_exception) throws Exception{
    // Get the Exception ID
    String id = p_exception.getMessage();

    // If ID is null or some other exception is reported then
    // assign it a default value
    if ((id == null) || (!id.startsWith("AQ"))){
      id = "AQ-1012";
    }

    // Get the Exception String to be displayed
    String displayString = (String)m_exceptionTable.get(id);

    p_request.setAttribute("Exception", displayString);

    return;
  }

}