struts-sandbox/mailreader-course/struts/lab-2-1-src/java/org/apache/struts/apps/mailreader/course/MemoryDatabasePlugIn.java

package org.apache.struts.apps.mailreader.course;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.struts.action.ActionServlet;
import org.apache.struts.action.PlugIn;
import org.apache.struts.apps.mailreader.dao.impl.memory.MemoryUserDatabase;
import org.apache.struts.config.ModuleConfig;

import javax.servlet.ServletException;
import java.io.*;

/**
 * <p><strong>MemoryDatabasePlugIn</strong> initializes and finalizes the
 * persistent storage of User and Subscription information for the Struts
 * Demonstration Application, using an in-memory database backed by an
 * XML file.</p>
 * <p/>
 * <p><strong>IMPLEMENTATION WARNING</strong> - If this web application is run
 * from a WAR file, or in another environment where reading and writing of the
 * web application resource is impossible, the initial contents will be copied
 * to a file in the web application temporary directory provided by the
 * container.  This is for demonstration purposes only - you should
 * <strong>NOT</strong> assume that files written here will survive a restart
 * of your servlet container.</p>
 *
 * @version $Rev: 360442 $ $Date: 2005-12-31 15:10:04 -0500 (Sat, 31 Dec 2005) $
 */
public class MemoryDatabasePlugIn implements PlugIn {

    // ---- Instance Variables ----

    /**
     * The {@link org.apache.struts.apps.mailreader.dao.impl.memory.MemoryUserDatabase} object we construct and make available.
     */
    private MemoryUserDatabase database = null;


    /**
     * Logging output for this plug in instance.
     */
    private Log log = LogFactory.getLog(this.getClass());


    /**
     * The {@link org.apache.struts.action.ActionServlet} owning this application.
     */
    private ActionServlet servlet = null;

    // ---- Properties ----

    /**
     * The web application resource path of our persistent database
     * storage file.
     */
    private String pathname = "/WEB-INF/database.xml";

    public String getPathname() {
        return (this.pathname);
    }

    public void setPathname(String pathname) {
        this.pathname = pathname;
    }

    // ---- PlugIn Methods ----


    /**
     * Gracefully shut down this database, releasing any resources
     * that were allocated at initialization.
     */
    public void destroy() {

        log.info("Finalizing memory database plug in");

        if (database != null) {
            try {
                database.close();
            } catch (Exception e) {
                log.error("Closing memory database", e);
            }
        }

        servlet.getServletContext().removeAttribute(Constants.DATABASE_KEY);
        database = null;
        servlet = null;
        database = null;
    }


    /**
     * Initialize and load our initial database from persistent storage.
     *
     * @param servlet The ActionServlet for this web application
     * @param config  The ApplicationConfig for our owning module
     * @throws ServletException if we cannot configure ourselves correctly
     */
    public void init(ActionServlet servlet, ModuleConfig config)
            throws ServletException {

        log.info("Initializing memory database plug in from '" +
                pathname + "'");

        // Remember our associated configuration and servlet
        this.servlet = servlet;

        // Construct a new database and make it available
        database = new MemoryUserDatabase();
        try {
            String path = calculatePath();
            if (log.isDebugEnabled()) {
                log.debug(" Loading database from '" + path + "'");
            }
            database.setPathname(path);
            database.open();
        } catch (Exception e) {
            log.error("Opening memory database", e);
            throw new ServletException("Cannot load database from '" +
                    pathname + "'", e);
        }

        // Make the initialized database available
        servlet.getServletContext().setAttribute(Constants.DATABASE_KEY,
                database);

    }

    // ---- Private Methods ----

    /**
     * Calculate and return an absolute pathname to the XML file to contain
     * our persistent storage information.
     *
     * @throws Exception if an input/output error occurs
     */
    private String calculatePath() throws Exception {

        // Can we access the database via file I/O?
        String path = servlet.getServletContext().getRealPath(pathname);
        if (path != null) {
            return (path);
        }

        // Does a copy of this file already exist in our temporary directory
        File dir = (File)
                servlet.getServletContext().getAttribute
                        ("javax.servlet.context.tempdir");
        File file = new File(dir, "struts-example-database.xml");
        if (file.exists()) {
            return (file.getAbsolutePath());
        }

        // Copy the static resource to a temporary file and return its path
        InputStream is =
                servlet.getServletContext().getResourceAsStream(pathname);
        BufferedInputStream bis = new BufferedInputStream(is, 1024);
        FileOutputStream os =
                new FileOutputStream(file);
        BufferedOutputStream bos = new BufferedOutputStream(os, 1024);
        byte buffer[] = new byte[1024];
        while (true) {
            int n = bis.read(buffer);
            if (n <= 0) {
                break;
            }
            bos.write(buffer, 0, n);
        }
        bos.close();
        bis.close();
        return (file.getAbsolutePath());

    }
}