ECMA 335 based classes can be accessed if at least one backend is running inside a ECMA complient VM, for example Novell's MONO or Microsoft's .NET. Special features such as varargs, reflection or assembly loading are also supported.

When the backend is running in a J2EE environment, session sharing between PHP and JSP is always possible. Clustering and load balancing is available if the J2EE environment supports these features.

Unlike previous attempts (the ext/java or the JSR 223 sample implementation) the PHP/Java Bridge does not use the java native interface ("JNI"). Php instances are allocated from the HTTP (Apache/IIS) pool, instances of java/j2ee components are allocated from the backend. The allocated instances communicate using a "continuation passing style", see java_closure() and the invocable interface. In case a php instance crashes, it will not take down the java application server or servlet engine.

Motivation

PHP components are essentially transient. For complex applications is usually necessary to introduce "middleware" components such as (enterprise-) "java beans" or enterprise applications which provide caching, connection pooling or the "business logic" for the pages generated by the PHP components. Parsing XML files for example is an expensive task and it might be necessary to cache the generated graph. Establishing connections to databases is an expensive operation so that it might be necessary to re-use used connections. The standard PHP XML or DB abstractions are useless in this area because they cannot rely on a middle tier to do caching or db connection pooling.

Even for trivial tasks it might be necessary to use a java class or java library. For example it might be necessary to generate Word, Excel or PDF documents without tying the application to a specific system platform.

PHP, the PHP/Java Bridge and the php files can be packaged within a standard J2EE archive, customers can easily deploy it into a J2EE application server or servlet engine. They don't have to install PHP and they usually cannot tell the difference whether the pages are generated by PHP, JSP or servlets. Since the bridge allows session sharing between PHP and the J2EE components, developers can migrate their JSP based solutions to PHP step by step.

PHP and the PHP/Java Bridge might also be interesting for java developers. There are a number of technologies based on the JSP template system such as jakarta Struts and its successor Java Server Faces. Since PHP/Java Bridge version 3.0 it is possible to embed php scripts into the JSF framework, so that UI developers can concentrate on developing HTML templates while web developers can create a prototype using php code and use the existing framework from their code.

Description

The bridge adds the following primitives to PHP. The type mappings are shown in table 1.

• new Java("CLASSNAME"): References and instanciates the class CLASSNAME. After script execution the referenced classes may be garbage collected. Example:
  
  

  <?php
$v = new Java("java.util.Vector");
$v->add($buf=new Java("java.lang.StringBuffer"));
$buf->append("100");
echo (int)($v->elementAt(0)->toString()) + 2;
?>


  
  
• new JavaClass("CLASSNAME"): References the class CLASSNAME without creating an instance. The returned object is the class object itself, not an object of the class. After script execution the referenced classes may be garbage collected. Example:
  
  

  $Object = new JavaClass("java.lang.Object");
$obj = $Object->newInstance();

$Thread = new JavaClass("java.lang.Thread");
$Thread->sleep(10);



  
  
• java_require("JAR1;JAR2"): Makes additional libraries available to the current script. JAR can either be a "http:", "ftp:", "file:" or a "jar:" or a default location. On "Security Enhanced Linux" (please see the README) the location must be tagged with a lib_t security context. Example:
  
  

  // load scheme interpreter
// try to load it from /usr/share/java/ or from sourceforge.net
java_require("kawa.jar");
java_require("http://php-java-bridge.sourceforge.net/kawa.jar");
$n=100;
$System = new JavaClass("java.lang.System");
$t1 = $System->currentTimeMillis();
$code="(letrec ((f (lambda(v) (if (= v 0) 1 (* (f (- v 1)) v))))) (f $n))";
$scheme = new java("kawa.standard.Scheme");
$res=(float)$scheme->eval($code);
echo "${n}! => $res\n";
$delta = $System->currentTimeMillis() - $t1;
echo "Evaluated in $delta ms.\n";


  
  
  
• java_context(): Makes the javax.script.ScriptContext available to the current script. All implicit web objects (session, servlet context, etc.) are available from the context, when the backend is running in a servlet engine or application server. The following example uses the jdk1.6 jrunscript to eval php statements interactively:
  
  

  /opt/jdk1.6/bin/jrunscript -l php-intractive
php-interactive> echo java_context()->getAttribute("javax.script.name");
=> STDIN



  
  
• java_closure(ENVIRONMENT, MAP, TYPE): Makes it possible to call PHP code from java. It closes over the PHP environment and packages it up as a java class. If the ENVIRONMENT is missing, the current environment is used. If MAP is missing, the PHP procedures must have the same name as the required procedures. If TYPE is missing, the generated class is "generic", i.e. the interface it implements is determined when the closure is applied. Example:
  
  

  <?php
  function toString() { return "hello" ; }
  echo (string)java_closure();
  ?>
  => hello

  
  
  Example which uses PHP and Mono:
  
  
  

  class GtkDemo {
  var $Application;

  function GtkDemo() {
    mono_require("gtk-sharp"); // link the gtk-sharp library
  }

  function delete($sender, $e) {
    echo "delete called\n";
    $this->Application->Quit();
  }
  function clicked($sender, $e) {
    echo "clicked\n";
  }
  function init() {
    $this->Application = $Application = new Mono("Gtk.Application");
    $Application->Init();

    $win = new Mono("Gtk.Window", "Hello");
    $win->add_DeleteEvent (
   new Mono(
    "GtkSharp.DeleteEventHandler",
    mono_closure($this, "delete")));

    $btn = new Mono("Gtk.Button", "Click Me");

    $btn->add_Clicked(
      new Mono(
       "System.EventHandler",
       mono_closure($this, "clicked")));
    $win->Add($btn);
    $win->ShowAll();
  }

  function run() {
    $this->init();
    $this->Application->Run();
  }
}
$demo = new GtkDemo();
$demo->run();


  
  
• $session=java_session(): Creates or retrieves a session context. When the backend is running in a J2EE environment, the session is taken from the request object, otherwise it is taken from PHP. Please see the ISession interface documentation for details. The java_session() must be called before the response headers have been sent and it should be called as the first statement within a php script.

  $session = java_session();
$servletRequest = $session->getHttpServletRequest();
$servletRequest->setAttribute(...);
...


  
  
• $session=java_session(SESSIONNAME): Creates or retrieves the session SESSIONNAME. This primitive uses a "private" session store with the name SESSIONNAME. Please see the ISession interface documentation for details. For java values $_SESSION['var']=val is syntactic shugar for java_session(session_id())->put('var', val).

  $session=java_session("testSession");
if($session->isNew()) {
   echo "new session\n";
   $session->put("a", 1);
   $session->put("b", 5);
} else {
   echo "cont session\n";
}
$session->put("a", $session->get("a")+1);
$session->put("b", $session->get("b")-1);

$val=$session->get("a");
echo "session var: $val\n";

if($session->get("b")==0) $session->destroy();


  The java_session primitive is meant for values which must survive the current script. If you want to cache data which is expensive to create, bind the data to a class. Example:

  // Compile this class, create cache.jar and copy it to /usr/share/java
public class Cache {
   public static Cache instance = makeInstance();
}

<?php
java_require("cache.jar");
$Cache = new JavaClass("Cache");
$instance=$Cache->instance; //instance will stay in the VM until the VM runs short of memory
?>


  
  
• JavaException: A java exception class. Available in PHP 5 and above only. Example:
  
  

  try {
  new java("java.lang.String", null);
} catch(JavaException $ex) {
   $trace = new java("java.io.ByteArrayOutputStream");
   $ex->printStackTrace(new java("java.io.PrintStream", $trace));
   print "java stack trace: $trace\n";
}


  
  
• foreach(COLLECTION): It is possible to iterate over values of java classes that implement java.util.Collection or java.util.Map. Available in PHP 5 and above only. Example:
  
  

  $conversion = new java("java.util.Properties");
$conversion->put("long", "java.lang.Byte java.lang.Short java.lang.Integer");
$conversion->put("boolean", "java.lang.Boolean");
foreach ($conversion as $key=>$value)
   echo "$key => $value\n";


  
  
• [index]: It is possible to access elements of java arrays or elements of java classes that implement the java.util.Map interface. Available in PHP 5 and above only. Example:
  
  

  $Array = new JavaClass("java.lang.reflect.Array");
$String = new JavaClass("java.lang.String");
$entries = $Array->newInstance($String, 3);
$entries[0] ="Jakob der Lügner, Jurek Becker 1937--1997";
$entries[1] ="Mutmassungen über Jakob, Uwe Johnson, 1934--1984";
$entries[2] ="Die Blechtrommel, Günter Grass, 1927--";
for ($i = 0; $i < $Array->getLength($entries); $i++) {
   echo "$i: " . $entries[$i] ."\n";
}


  
  
• java_instanceof(JAVA_OBJ, JAVA_CLASS): Tests if JAVA_OBJ is an instance of JAVA_CLASS. Example:
  
  

  $Collection=new JavaClass("java.util.Collection");
$list = new java("java.util.ArrayList");
$list->add(0);
$list->add(null);
$list->add(new java("java.lang.Object"));
$list->add(new java("java.util.ArrayList"));
foreach ($list as $value) {
   if($value instanceof java && java_instanceof($value, $Collection))
     /* iterate through nested ArrayList */
   else
     echo "$value\n";
}


  
  
• java_last_exception_get(): Returns the last exception instance or null. Since PHP 5 you can use try/catch instead.
  
  
• java_last_exception_clear(): Clears the error condition. Since PHP 5 you can use try/catch instead.

Custom java libraries (.jar files) can be stored in the following locations:

1. Somewhere on a HTTP or FTP server, see PHP function java_require. On Security Enhanced Linux .jar files can only be loaded from locations which are tagged with the lib_t security context.
2. In the sub-directory "lib" of the PHP extension directory, if it exists and is accessible when the JVM starts the bridge. This is usually "`php-config --extension-dir`/lib". On Security Enhanced Linux this directory is tagged with the lib_t security context.
3. In the /usr/share/java/ directory, if it exists and is accessible when the JVM starts the bridge. On Security Enhanced Linux this directory is tagged with the lib_t security context.

The PHP/Java Bridge can operate in 4 different modes:

1. Invoked from the dl() function. In this mode the bridge starts when the HTTP server receives a client request and terminates after the response is written. This is very slow because it starts a new backend (Java or .NET VM) for each request. But it does not require any administrative privileges.
2. Permanently activated in the global php.ini file with an internal java process running in the HTTP server domain. In this mode the bridge backend starts when the HTTP server starts and terminates when the HTTP server terminates. Recommended during development. Please see web server installation below.
3. Permanently activated in the global php.ini file with an external java process. Recommended for production systems. This mode is used by the RPM package available for RedHat Enterprise Linux. In this mode the bridge starts and stops as a system service.
4. Permanently activated in the global php.ini file with an external application server or servlet engine. PHP be can run as a CGI sub-component within a pure java application server or be installed as a Apache/IIS module.