servlet中使用db4o

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      在web的工程如果想使用db4o，是不能直接使用的，如果想使用的就得做一些初始化的工作，以便在servlet中使用，具体可以看下面的两个网页有详细的介绍：

  http://java.dzone.com/articles/db4o-java

 http://community.versant.com/documentation/reference/db4o-8.1/java/reference/Content/platform_specific_issues/web/servlets.htm

  可以如此使用：

   Db4oServletContextListener.java

import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

import com.db4o.Db4oEmbedded;
import com.db4o.EmbeddedObjectContainer;
import com.db4o.ObjectContainer;
import com.db4o.config.EmbeddedConfiguration;

public class Db4oServletContextListener 
	implements ServletContextListener {

	public static final String PREFIX_PATH = "E:/Pattern/PDFBox-v2/";
	public static final String KEY_DB4O_FILE_NAME = "db4oFileName";
	public static final String KEY_DB4O_SERVER = "db4oServer";
	
	
	@Override
	public void contextInitialized(ServletContextEvent event) {
		System.out.println("context oK");
	    ServletContext context = event.getServletContext();
	    String filePath = PREFIX_PATH + context.getInitParameter(KEY_DB4O_FILE_NAME);
	    EmbeddedConfiguration configEmbedded = Db4oEmbedded.newConfiguration();
	    EmbeddedObjectContainer rootContainer = Db4oEmbedded.openFile(configEmbedded,
				filePath);
	    context.setAttribute(KEY_DB4O_SERVER, rootContainer);
	   /* ArrayList<exam> result = new ArrayList<exam>();
		ObjectSet<exam> objectSet = rootContainer.query(exam.class);
		while (objectSet.hasNext()) {
			result.add((exam) objectSet.next());
		}
		exam[] exams = result.toArray(new exam[result.size()]);
		System.out.println(exams.length);*/
	    context.log("db4o startup on " + filePath);
	}


	@Override
	public void contextDestroyed(ServletContextEvent event) {
	    ServletContext context = event.getServletContext();
	    ObjectContainer rootContainer = (ObjectContainer) context.getAttribute(KEY_DB4O_SERVER);
	    context.removeAttribute(KEY_DB4O_SERVER);
	    close(rootContainer);
	    context.log("db4o shutdown");
	}
	
	private void close(ObjectContainer container) {
		if(container != null) {
			container.close();
		}
	}
}

   自己的servlet代码：

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.db4o.EmbeddedObjectContainer;

public class CategoryServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
	
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		doPost(request, response);
	}

	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		System.out.println("OK");
		EmbeddedObjectContainer container = (EmbeddedObjectContainer) 
				request.getServletContext().getAttribute("db4oServer");
	}}