Java Web Apps

One-sentence summary of this page.

Introduction

The database instances are not thread-safe, so each thread needs a own instance. All the database instances will share the same connection to the storage for the same URL. For more information look at Java Multi threads and databases.

Java WebApp runs inside a Servlet container with a pool of threads that work the requests.

There are mainly 2 solutions:

• Manual control of the database instances from Servlets (or any other server-side technology like Apache Struts Actions, Spring MVC, etc.)
• Automatic control using Servlet Filters

Manual control

    package com.orientechnologies.test;
    import javax.servlet.*;
    
    public class Example extends HttpServlet {
      public void doGet(HttpServletRequest request,
                        HttpServletResponse response)
            throws IOException, ServletException
      {
        ODatabaseDocument database = ODatabaseDocumentPool.global().acquire("local:/temp/db", "admin", "admin");
    
        try {
    
         // USER CODE
    
        } finally {
          database.close();
        }    
      }
    }

Automatic control using Servlet Filters

Servlets are the best way to automatise database control inside WebApps. The trick is to create a Filter that get a database from the pool and binds it in current ThreadLocal before to execute the Servlet code. Once returned the ThreadLocal is cleared and database released to the pool.

JaveEE Servlets

Create a Filter class

Create a database instance per request

In this example a new database instance is created per request, opened and at the end closed.

    package com.orientechnologies.test;
    import javax.servlet.*;
    
    public class OrientDBFilter implements Filter {
    
      public void doFilter(ServletRequest request, ServletResponse response,
              FilterChain chain) {
          ODatabaseDocument database = new ODatabaseDocumentTx("local:/temp/db").open("admin", "admin");
          try{
            chain.doFilter(request, response);
          } finally {
            database.close();
          }
      }
    }

Use the database pool

In this example the database pool is used.

    package com.orientechnologies.test;
    import javax.servlet.*;
    
    public class OrientDBFilter implements Filter {
    
      public void doFilter(ServletRequest request, ServletResponse response,
              FilterChain chain) {
          ODatabaseDocument database = ODatabaseDocumentPool.global().acquire("local:/temp/db", "admin", "admin");
          try{
            chain.doFilter(request, response);
          } finally {
            database.close();
          }
      }
    
      public void destroy() {
          ODatabaseDocumentPool.global().close();
      }
    }

Register the filter

Now we've create the filter class it needs to be registered in the web.xml file:

    <?xml version="1.0" encoding="UTF-8"?>
    <web-app xmlns="http://java.sun.com/xml/ns/j2ee"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee 
             http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"
             version="2.4">  
      <filter>     
        <filter-name>OrientDB</filter-name>   
        <filter-class>com.orientechnologies.test.OrientDBFilter</filter-class>  
      </filter> 
        <filter-mapping>   
          <filter-name>OrientDB</filter-name>   
          <url-pattern>/*</url-pattern>   
        </filter-mapping> 
        <session-config>   
          <session-timeout>30</session-timeout>   
        </session-config> 
    </web-app>