As you can gather from the title of this website, I create software in Java, Scala, and PHP. While Java and Scala compile to bytecode that runs on the same virtual machine, PHP is executed by a separate interpreter. The most efficient way to run PHP scripts is to integrate the interpreter directly into the webserver. Hence, most PHP developers use a local Apache Httpd server with mod_php for development. If you also do Java programming, this raises the problem that you need two different web servers, namely Tomcat (or another web container or appserver) for Java development and Apache for PHP development. Running two servers is a bit of a nuisance. Two servers consume more resources than one and you cannot run both on the same port. This problem can be solved in three different ways: you can only run one server at a time, you can use a different port number for one server which has to be included in the URLs, or you can integrate the two servers. There are again at least three different ways to accomplish the latter: you can proxy requests from Apache to Tomcat, you can proxy request from Tomcat to Apache, or you can use a connector module, such as mod_jk. Of course, maintaining two servers is is more complicated than maintaining one, and the integration adds additional complexity. Fortunately, there is an easier way to integrate PHP and Java web applications. PHP/Java Bridge is a free open source product for the integration of the native PHP interpreter with the Java VM. It is designed with web applications in mind: Java servlets can “talk” to PHP scripts and vice versa. The official website describes it as an “implementation of a streaming, XML-based network protocol which is up to 50 times faster than local RPC via SOAP.” PHP/Java Bride requires no additional components to invoke Java procedures from PHP or vice versa. Although there are a number of different use cases, I am going to describe a particular one in this article, namely how to configure Tomcat with PHP/Java Bridge in order to have Tomcat serve PHP web pages. Let’s start with software requirements. We need the following software packages:

• A Java virtual machine (JRE is sufficient, but JDK recommended for developers)
• A recent version of Apache Tomcat (http://tomcat.apache.org)
• A recent version of PHP (standalone, without Webserver: http://php.net)
• PHP/Java Bridge (http://php-java-bridge.sourceforge.net/pjb/)

Follow the standard installation procedures for the JVM, Tomcat, and PHP. On Linux, you can use the standard packages for your distribution and on Windows you can use the regular installers. Make sure that both Tomcat and PHP are installed properly, which means that you should see Tomcat’s welcome web page at http://localhost:8080 and you should be able to execute a PHP script via the command line by invoking the standalone “php” command. The PHP/Java Bridge product does not use the regular executable, however, but fast CGI. The fast CGI executable is called php-cgi (or Php.cgi.exe on Windows), so you must make sure that your PHP installation contains it. Then you are all set to install and configure the PHP/Java Bridge. The PHP/Java Bridge package comes with a sample web application named JavaBridge.war. Deploy the application in Tomcat, point your browser to http://localhost:8080/JavaBridge and try out the examples. If this works, you are half-finished. To provide the capability to execute PHP scripts server-wide, not just in a single web application, you need to make some changes to the Tomcat configuration. Find the three jar files named JavaBridge.jar, php-servlet.jar and php-script.jar (look in WEB-INF/lib) and move them to Tomcat’s shared library directory. This is usually found in $CATALINA_HOME/lib (or $CATALINA_HOME/shared in older Tomcat installations). Then edit Tomcat’s conf/web.xml configuration file and add the following lines:

<listener-class>
    php.java.servlet.ContextLoaderListener
  </listener-class>
</listener>

<servlet>
  <servlet-name>PhpJavaServlet</servlet-name>
  <servlet-class>
    php.java.servlet.PhpJavaServlet
  </servlet-class>
</servlet>

<servlet>
  <servlet-name>PhpCGIServlet</servlet-name>
  <servlet-class>
    php.java.servlet.PhpCGIServlet
  </servlet-class>
  <init-param>
<param-name>prefer_system_php_exec</param-name>
<param-value>On</param-value>
  </init-param>
  <init-param>
<param-name>php_include_java</param-name>
<param-value>On</param-value>
  </init-param>
</servlet>

<servlet-mapping>
  <servlet-name>PhpJavaServlet</servlet-name>
  <url-pattern>*.phpjavabridge</url-pattern>
</servlet-mapping>

<servlet-mapping>
  <servlet-name>PhpCGIServlet</servlet-name>
  <url-pattern>*.php</url-pattern>
</servlet-mapping>

This adds the listeners and servlets required for PHP script execution to all web applications. While you are at it, you might also want to enable index.php files to display when a directory URL is requested. Simply add it to the list of welcome files in conf/web.xml. My list looks like this:

<welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>index.php</welcome-file>
</welcome-file-list>

Now you can copy PHP scripts into the context root directory of any web application and type the script URL into your browser. I suggest you try a script with phpinfo(). It gives you plenty of useful configuration info. If this doesn’t work and you are on Unix, the problem might be file permissions. On my machine, I had to copy the contents of “java” directory in the JavaBridge webapp manually to the context root directory where PHP applications were installed. This directory contains two files Java.inc and JavaProxy.php. Normally, the PHP/Java Bridge software copies it automatically, but it might not be able to do so if it does not have proper permissions:

~$ ls -lh /var/lib/tomcat6/webapps/ROOT/java
total 136K
-rw-rw-r-- 1 root root 64K 2009-12-30 14:14 Java.inc
-rw-rw-r-- 1 root root 64K 2009-12-30 14:14 JavaProxy.php

Now try calling a PHP script. For example, a script containing the phpinfo() command displays information about the server: I have configured my machine to host all PHP web applications in Tomcat’s ROOT context. This eliminates the extra path component of the webapp context, since the ROOT’s context path is “/”. Then I softlinked the folder that contains all my PHP projects into the ROOT webapp directory, so that the actual source files are kept separate from the Tomcat installation. In order to enable Tomcat to follow symlinks, you need to edit the context.xml of the respective web application -in this case ROOT- and add the line: <Context path=”/” allowLinking=”true” /> . Another possible gotcha is Tomcat’s security manager, which is enabled by default on Ubuntu, but not on Windows. Although a security manager is not necessary for most development scenarios, it is highly recommended for production. I consider it good practice to enable the security manager on the development machine, because it allows me to recognise security problems early during development, before the application is deployed on the production server. The downside is that additional configuration may be required, for PHP applications to function properly. The respective configuration files are located in $CATALINA_BASE/conf/policy.d. Most likely, you need to grant PHP web applications write access to files in the document root and possibly other permissions, such as opening sockets, etc. It’s probably safest to do this on a per-application basis.