VM Bridge FAQ

General questions

Which alternatives exist?

There are at least 4 other php to java bridges which offer a similar API. One was distributed with PHP 4.0.0 and has been discontinued. Two other bridges are proprietary software, built into a vendor-specific framework from Zend or a J2EE application server from Caucho. Furthermore IBM's Zero framework for Eclipse contains a PHP interpreter written in pure Java and a php to java bridge which can call Java methods in-process.

The only free alternatives are SOAP and XML-RPC, which are up to 50 times slower than the XML protocol implementation used by this VM Bridge.

How do I enable the Java extension in my php.ini file?

A Java extension does not exist, so you can't enable it.

The VM Bridge is a network protocol, it requires a running Java VM, for example the servlet container Apache/Tomcat. Or, if you want to call PHP libraries from Java, a running PHP container, e.g. Apache or IIS.

What do I need to communicate with Java?

Only the PHP code from Java.inc and a running Java application, for example JavaBridge.jar, or a running Java servlet, for example JavaBridge.war.

What do I need to communicate with PHP?

Only the PHP code from JavaProxy.php within your PHP web application and the Java libraries JavaBridge.jar, php-script.jar and php-servlet.jar.

Which versions are supported?

• PHP >= 5.1.2. PHP >= 5.3 recommended.
• Java >= 1.4. Java >= 6 recommended.
• J2EE >= 1.3. For J2EE 1.3 remove the RequestListener declaration from the WEB-INF/web.xml.
• Mono >= 1.2.4 or .NET >= 2.

Do I need a Java Application Server or Servlet Engine?

Java needs an execution environment.

You can also add PHP support to your standalone Java application by adding the following line to its main class:

static final php.java.bridge.JavaBridgeRunner runner = php.java.bridge.JavaBridgeRunner.getInstance(8087);

The third option is the standard JSR 223 script interface, which allows one to execute PHP code/scripts from Java applications.

Ho do I enable logging?

Copy log4j.jar into java.ext.dirs. Example for JDK 6:

cp log4j.jar /usr/java/packages/lib/ext

Start the log4j viewer. Example for JDK 6:

/opt/jdk1.6/bin/java org.apache.log4j.chainsaw.Main

Start the application server with the options -Dphp.java.bridge.default_log_level=LEVEL. Example for tomcat:

JAVA_HOME=/opt/jdk1.6 JAVA_OPTS="-Dphp.java.bridge.default_log_level=5" bin/catalina.sh run

java -Dphp.java.bridge.default_log_level=5 -jar JavaBridge.jar SERVLET:8080

How can I set Java options?

With the -D flag. See java -jar JavaBridge.jar --help for details. If tomcat is being used, one can set these options as follows:

JAVA_OPTS="-D... -D..." /opt/tomcat/bin/catalina.sh run

You probably haven't required the relevant Java library. Or the class doesn't exist or it is not public or it throws a java.lang.Error during initialization. Check which library exports the feature and add the library to the java_require() statement.

Why do I get a NoClassDefFoundError?

Because Java doesn't have a module system.

All libraries and their dependencies must be loaded by one, and only one class loader.

Please read the previous sentence until you understand what it means; for example a simple file system copy(!) operation may be the cause for a NoClassDefFoundError.

Please do not report NoClassDefFoundErrors to the mailing list or via the bug tracker. This is not a bug and we cannot help you any further!

I cannot require my JDBC driver!?!

Please re-read the class loading section. The following code loads all interconnected libraries using a single java_require() call:

  java_require("myApplication.jar;myJdbcDriver.jar");
   ...
  $myApplication->callWithMyJdbcDriver();


The following incorrect code fails because the application (the "JavaBridge.jar" in this case) cannot be accessed by the jdbc driver. This constraint is checked by the DriverManager:

  java_require("myJdbcDriver.jar"); // WRONG!
  new java("my.jdbc.Driver");
  java("java.sql.DriverManager")->getDriver("myJdbcURL"); // FAILS!


How do I load impure Java libraries?

You can't. Java libraries must be pure Java.

Please read the documentation of your J2EE server, Servlet engine or Java VM to see if and how the environment can handle impure Java libraries. A common approach is to store the Java part in java.ext.dirs and the native part in java.library.path.

J2EE/Servlet questions

Set up the VM Bridge cluster as described below. The example uses two nodes named "carlos" and "diego". The HTTP server front end runs on the web server "timon".

Install Apache 2.2.0 or higher.

Enable proxy_module and proxy_balancer_module. The following example is for Linux (lines marked with "+" should be added to the conf/httpd.conf file):

   LoadModule rewrite_module modules/mod_rewrite.so
 + LoadModule proxy_module modules/mod_proxy.so
 + LoadModule proxy_balancer_module modules/mod_proxy_balancer.so
   LoadModule cache_module modules/mod_cache.so


Add the following code to the bottom of your conf/httpd.conf file:

ProxyPass /JavaBridge balancer://mycluster maxattempts=2
<Proxy balancer://mycluster>
  BalancerMember http://diego:8080/JavaBridge
  BalancerMember http://carlos:8080/JavaBridge
</Proxy>
<Location /balancer-manager>
  SetHandler balancer-manager
  Deny from all
  Allow from 127.0.0.1
</Location>


Start the cluster nodes on "carlos" and "diego".

Browse to http://timon/JavaBridge/ (note the trailing slash) and click on the test.php. Click on refresh. Check if both nodes respond.

Browse to http://timon/JavaBridge/sessionSharing.php and click on refresh. Check the cookie value.

Browse to http://timon/balancer-manager/.

Please see the mod_rewrite documentation for more information how to rewrite incoming URLs.

Please see your HTTP server documentation and the description above how to set it up as a load balancer.

1. Download and install the J2EE binary: copy JavaBridge.war into the tomcat webapps folder.
   
2. Start tomcat, for example with:

   JAVA_HOME=/usr/java/default /opt/tomcat/bin/catalina.sh run

3. Move(!) all libraries from the created webapps/JavaBridge/WEB-INF/lib folder to the tomcat lib folder and remove(!) webapps/JavaBridge/WEB-INF/web.xml. The only reason to keep the JavaBridge directory is the WEB-INF/cgi/launcher* FastCGI launcher and the java/Java.inc files. Example:

   mv /opt/tomcat/webapps/JavaBridge/WEB-INF/lib/* /opt/tomcat/lib
rm /opt/tomcat/webapps/JavaBridge/WEB-INF/web.xml

4. Stop tomcat and remove webapps/JavaBridge.war. Make sure that webapps/JavaBridge still exists, but without any libraries and web.xml!

5. Add the lines marked with a + to the tomcat conf/web.xml:

   
<!-- ================== Built In Servlet Definitions ==================== -->

+ <!-- PHP Servlet -->
+ <listener> <listener-class>php.java.servlet.ContextLoaderListener</listener-class> </listener>
+ <listener> <listener-class>php.java.servlet.RequestListener</listener-class> </listener>
+ <servlet>
+ <servlet-name>GlobalPhpJavaServlet</servlet-name>
+ <servlet-class>php.java.servlet.PhpJavaServlet</servlet-class>
+ </servlet>
+ <!-- PHP CGI Servlet -->
+ <servlet>
+ <servlet-name>GlobalPhpCGIServlet</servlet-name>
+ <servlet-class>php.java.servlet.PhpCGIServlet</servlet-class>
+ <init-param> <param-name>shared_fast_cgi_pool</param-name><param-value>On</param-value></init-param>
+ <init-param> <param-name>prefer_system_php_exec</param-name><param-value>On</param-value></init-param>
+ </servlet>

<!-- The default servlet for all web applications, that serves static -->
<!-- resources. It processes all requests that are not mapped to other -->
[...]
<!-- ================ Built In Servlet Mappings ========================= -->

+ <!-- PHP Servlet Mapping -->
+ <servlet-mapping>
+ <servlet-name>GlobalPhpJavaServlet</servlet-name>
+ <url-pattern>*.phpjavabridge</url-pattern>
+ </servlet-mapping>
+ <!-- CGI Servlet Mapping -->
+ <servlet-mapping>
+ <servlet-name>GlobalPhpCGIServlet</servlet-name>
+ <url-pattern>*.php</url-pattern>
+ </servlet-mapping>

<!-- The servlet mappings for the built in servlets defined above. Note -->
<!-- that, by default, the CGI and SSI servlets are *not* mapped. You -->

</web-app>


6. Start tomcat again.

Create a directory myApplication, create the directories myApplication/WEB-INF/lib/ and myApplication/WEB-INF/cgi/. Download the J2EE binary and copy the JavaBridge.jar and the php-servlet.jar from the JavaBridge.war to the myApplication/WEB-INF/lib/ folder. Copy the contents of the cgi folder to myApplication/WEB-INF/cgi/. Create the file myApplication/WEB-INF/web.xml with the following content:


<web-app>
<!-- PHP Servlet -->
<servlet>
<servlet-name>PhpJavaServlet</servlet-name>
<servlet-class>php.java.servlet.PhpJavaServlet</servlet-class>
</servlet>
<!-- PHP CGI processing servlet, used when Apache/IIS are not available -->
<servlet>
<servlet-name>PhpCGIServlet</servlet-name>
<servlet-class>php.java.servlet.PhpCGIServlet</servlet-class>
</servlet>

<!-- PHP Servlet Mapping -->
<servlet-mapping>
<servlet-name>PhpJavaServlet</servlet-name>
<url-pattern>*.phpjavabridge</url-pattern>
</servlet-mapping>
<!--PHP CGI Servlet Mapping -->
<servlet-mapping>
<servlet-name>PhpCGIServlet</servlet-name>
<url-pattern>*.php</url-pattern>
</servlet-mapping>

<!-- Welcome files -->
<welcome-file-list>
<welcome-file>index.php</welcome-file>
</welcome-file-list>
</web-app>


To call Java code from PHP, copy the java/Java.inc to some directory and require it as usual, e.g.: require_once("java/Java.inc");.

To call PHP code from Java, copy the java/JavaProxy.php to some webdirectory and use the EngineFactory as usual, e.g.: EngineFactory.getInvocablePhpScriptEngine(this, application, request, response); or, if PHP is running somewhere else: EngineFactory.getInvocablePhpScriptEngine(..., 80, "/phpApp/JavaProxy.php");.

Copy the files sessionSharing.jsp and sessionSharing.php from the JavaBridge.war to myApplication and create myApplication.war, for example with the commands: cd myApplication; jar cf ../myApplication.war *.

The web archive can now be distributed, copy it to the tomcat webapps directory and re-start tomcat. Visit http://localhost/myApplication/sessionSharing.php and http://localhost/myApplication/sessionSharing.jsp.

Install the PHP/Java Bridge for all web application as described here.

Set up Apache or IIS so that it forwards requests to the back end. Please see the description above for details.

Does the bridge run native code within my servlet engine or application server?

No. The bridge back end is written in pure java, it doesn't use any native code. Native PHP runs within Apache, IIS, a FCGI server or via CGI. If the PHP instance crashes, an error page is returned to the client and the Apache, IIS, CGI container usually starts a new PHP instance for the next request.

If you see the message:

Warning: fsockopen() [function.fsockopen]: unable to connect to ssl://127.0.0.1:8443 (Unable to find the socket transport "ssl" - did you forget to enable it when you configured PHP?)

A workaround is to use the official non-SSL port or to open a dedicated local port for the PHP-Java communication. The following example is for Tomcat:

Disable override_hosts in the web application WEB-INF/web.xml:

<context-param>
<param-name>override_hosts</param-name>
<param-value>Off</param-value>
</context-param>


Either fetch the Java.inc directly from your back end (which also adjusts the JAVA_HOSTS) or change the JAVA_HOSTS option, for example:

define("JAVA_HOSTS", "127.0.0.1:9090");

Restart the application server or servlet engine. Check the settings by running phpinfo() or by visiting the test.php page.

The EJB example works with the Sun J2EE server, but in JBoss I get a ClassCastException, what's wrong?

It's a JBoss problem, although this problem may also appear in other application servers which do not strictly separate the application/bean domains. The JavaBridge.war already contains the documentClient.jar as a library, so JBoss references the library classes instead of the bean classes. Just remove the documentClient.jar from the JavaBridge.war, re-deploy JavaBridge.war and run the test again.

In JBoss' default setup the code:

// access the home interface
$DocumentHome = new JavaClass("DocumentHome");
$PortableRemoteObject = new JavaClass("javax.rmi.PortableRemoteObject");
$home=$PortableRemoteObject->narrow($objref, $DocumentHome);


In contrast the Sun J2EE server correctly separates the beans/applications; the $objref is a unique proxy generated by a parent of the WebAppClassLoader, so that narrow can always cast the proxy to DocumentHome@WebAppClassLoader, even if a class with the same name is already available from the WebAppClassLoader.

How do I install PHP into the Nutch, Spring, JSF, ..., Framework?

By providing JSR 223 based PHP beans and a description how to manage them, as usual. The code

javax.script.ScriptEngine e =
php.java.script.EngineFactory.getInvocablePhpScriptEngine (this,
application,
request, response);


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

General runtime questions

How do I reference a class w/o creating an instance?

With the java function, for example: java("java.lang.System").

The function is defined in http://localhost:8080/JavaBridge/java/Java.inc as:

function java($clazz) {
  static $classMap = array();
  if(array_key_exists($clazz, $classMap)) return $classMap[$clazz];
  return classMap[$clazz]=new JavaClass($clazz);
}

Why does java_context()->getHttpServletRequest()->getSession() return null?

PHP scripts must explicitly allocate a session with java_session(). For example:

java_session();
// now the (Remote-)HttpServletRequest knows about the session:
echo java_context()->getHttpServletRequest()->getSession();


Where is my output?

System.out and System.err are redirected to the server log file(s). When PHP scripts are invoked from a java framework (Java Server Faces for example), even the PHP output is redirected. For the standalone back end the output appears in the /var/log/php-java-bridge.log or in VMBridge.log, see .ini option java.log_file. For the j2ee back end the location of the log file(s) depends on the j2ee server configuration.

How do I make my script state (objects or variables) persistent?

If you must code it yourself: with e.g. java_session()->put("buf", $stringBuffer)

How many threads does the bridge start?

Request-handling threads are started from a thread pool, which limits the number of user requests to 20 (default), see system property php.java.bridge.threads. All further requests have to wait until one of the worker threads returns to the pool.

When running in a servlet engine, a ContextServer is started which handles the pipe or local socket communication channel.

When java invokes local scripts outside of a HTTP environment, the bridge starts a HttpServer, a ContextServer and a HttpProxy. The HttpProxy represents the PHP continuation and the HttpServer the request-handling java continuation associated with the JSR223 script.

How do I access enums or inner classes?

How do I create a primitive array?

Primitive types are wrapped by associated java classes. The following example uses reflect.Array to create a new byte array:

$Byte = new JavaClass("java.lang.Byte");
$byte = $Byte->TYPE;
$Array = new JavaClass("java.lang.reflect.Array");
$byteArray = $Array->newInstance($byte, 255);
$System = new JavaClass("java.lang.System");
$length = $System->in->read($byteArray);
$str = new Java("java.lang.String", $byteArray, 0, $length);
echo "You have typed: $str\n";


How fast is it?

The following scripts were executed on one 1.688 GHZ x86 cpu running RedHat Fedora Core 4 Linux and Sun jdk1.6.0_02:

<?php
$buf=new java("java.lang.StringBuffer");

$i=0;
while($i<400000) {
  $i=$i+1;
  $buf->append($i);
}

print $buf->length() . "\n";
?>


buf = new java.lang.StringBuffer();
for(i=0; i<400000; i++) buf.append(new String(i));
print (buf.toString().length());


How does the bridge handle OutOfMemoryErrors?

OutOfMemoryErrors may happen because a cached object cannot be released, either because

1. the object is permanently referenced by a request-handling thread or
2. the object has been entered into the session or application store or the object is referenced by a thread outside of the scope of the VM Bridge.

When a java.lang.OutOfMemoryError reaches the request-handling thread, the VM Bridge thread pool removes the thread from its pool and writes a message FATAL: OutOfMemoryError to the VM Bridge log file. The session store is cleaned and all client connections are terminated without confirmation.

If the OutOfMemoryError persists, this means that a thread outside of the VM Bridge has caused this error condition.

OutOfMemory conditions can be debugged by running the back end with e.g.:

java -agentlib:hprof=heap=sites -jar JavaBridge.jar


How can PHP classes extend Java classes and Java methods?

By using java_closure() and the visitor pattern for example. The tests.php5 folder contains a script_api.php example which shows how to implement java.lang.Runnable to run multiple PHP threads, concurrently accessing a shared resource.

How can I execute PHP code on the server?

With java_begin_document()/java_end_document(). For example:

  java_begin_document();
  $s = new Java("java.lang.StringBuffer");
  for($i=0; $i<10000; $i++) $s->append($i);
  java_end_document();


How can I convert a Java object into a PHP value?

With java_values(). For example:

  $s = new Java("java.lang.String");
  $c = $chr = $s->toCharArray();
  print (java_values($s));
  print_r(java_values($c));


How can I convert a PHP object into a Java object?

With java_closure(). For example:

  class Foo {
   function toString() {return "php::foo";}
  }
  $foo = new Foo();
  $jObj = java_closure($foo);
  $String = new Java("java.lang.String");
  echo $String->valueOf($jObj);


How do I call JSP tags from PHP?

Example:

require_once("http://localhost:8080/JavaBridge/java/Java.inc");
java_require("myLibs/baz-taglib.jar");
$tag = new Java("foo.bar.BazTag");

$session = java_session();
$ctx = java_context();
$servlet = $ctx->getAttribute("php.java.servlet.Servlet");
$response = $ctx->getAttribute("php.java.servlet.HttpServletResponse");
$request = $ctx->getAttribute("php.java.servlet.HttpServletRequest");
$factory = java("javax.servlet.jsp.JspFactory")->getDefaultFactory();
$pc = $factory->getPageContext($servlet, $request, $response, null, true, 8192, false);

$tag->setPageContext($pc);
$value = $tag->doStartTag();
if(($value != Java("javax.servlet.jsp.tagext.Tag")->SKIP_BODY) {
  if($value != Java("javax.servlet.jsp.tagext.Tag")->EVAL_BODY_INCLUDE)) {
    $tag->setBodyContent($pc->pushBody());
    $tag->doInitBody();
  }
  do {
    ...
  } while($tag->doAfterBody() == Java("javax.servlet.jsp.tagext.BodyTag")->EVAL_BODY_AGAIN)
}
if($value != Java("javax.servlet.jsp.tagext.Tag")->EVAL_BODY_INCLUDE) $pc->popBody();
$tag->doEndTag();


The generated content (if any) can be retrieved from the servlet output stream with:

java_values($response->getBufferContents();

Please see the php_java_lib/JspTag.php and tests.php5/tag.php for details.

How does the bridge support Java generics?

You can ignore the parameter type.

Java doesn't support real generics on byte-code level. The generics in JDK 1.5 and above are implemented as "erasures"; they are syntactic sugar, useful only for the Java compiler. The generated byte-code is the same as in JDK 1.4.

What about Java 5 varargs?

Pass them as a PHP array. Example:

<?php require_once("http://localhost:8080/JavaBridge/java/Java.inc");
$here=getcwd(); java_require("$here/varargs.jar");
$t1 = new java('Varargs$Test', 1);
$t2 = new java('Varargs$Test', 2);
echo java("Varargs")->varargs(array($t1, $t2));
?>

public class Varargs {
 public static class Test {
  public int i;
  public Test (int i) {
   this.i = i;
  }
  public String toString() {
   return String.valueOf(i);
  }
 }
 public static String varargs(Test ...tests) {
  StringBuffer buf = new StringBuffer();
  for (Test test : tests) {
   buf.append(test);
  }
  return buf.toString();
 }
}


NULL tests

Use java_is_null($value) or is_null (java_values ($value)) to test for a (Java-) NULL value.

How do I start the bridge back end when there's another Java VM listening on port 8080?

Simply deploy the VM Bridge web archive into the servlet engine or application server listening on port 8080. Or use a different port.

What's the difference between SERVLET_LOCAL:8080 and INET_LOCAL:8080?

The standalone option SERVLET_LOCAL emulates a servlet engine and starts a HTTP server which can select the fastest channel supported on this operating system. On Linux this is a named pipe created in /dev/shm or INET_LOCAL as a fall back.

INET_LOCAL always uses local TCP socket communication.

Whenever I reboot my computer I have to start the bridge back end again. How can I automate this?

Download and install a servlet engine or J2EE server as a Windows or Unix service.

Do I have to require Java.inc in each of my scripts? Isn't that very slow?

In order to communicate with Java, a PHP "Java" class definition is needed. Here's a simple PHP "Java" class definition which fits into one line:

<?php
// The following is the "Java" class definition, stripped down to fit into one line
// To use this sample start Java with: java -jar JavaBridge.jar INET:9267
// Or enable java.so or php_java.dll, which automatically start the above
// process Then type: php sample.php
//
class P {const Pc="<C v=\"%s\" p=\"I\">", PC="</C>"; const Pi="<I v=\"%d\" m=\"%s\" p=\"I\">", PI="</I>"; const Ps="<S v=\"%s\"/>", Pl="<L v=\"%d\" p=\"%s\"/>", Po="<O v=\"%d\"/>"; private $c; function str($s){fwrite($this->c, sprintf(self::Ps, $s));} function obj($s){fwrite($this->c, sprintf(self::Po, $s->java));} function __construct(){$this->c=fsockopen("127.0.0.1",9267);} function cBeg($s){fwrite($this->c, sprintf(self::Pc, $s));} function cEnd(){fwrite($this->c, self::PC);} function iBeg($o, $m){fwrite($this->c, sprintf(self::Pi, $o, $m));} function iEnd(){fwrite($this->c, self::PI);} function val($s){if(is_object($s))$this->obj($s);else $this->str((string)$s);} function res(){$r=sscanf(fread($this->c, 8192),"%s v=\"%[^\"]\"");return $r[1];}} function gP() {static $p; if(!$p) $p=new P(); return $p;} class Java {var $java, $p; function __construct() {if(!func_num_args()) return; $this->p=gP(); $ar=func_get_args(); $this->p->cBeg(array_shift($ar)); foreach($ar as $arg) $this->p->val($arg); $this->p->cEnd(); $ar = sscanf($this->p->res(), "%d"); $this->java=$ar[0];} function __call($meth, $args) {$this->p->iBeg($this->java, $meth); foreach($args as $arg) $this->p->val($arg); $this->p->iEnd(); $proxy = new Java(); $ar = sscanf($this->p->res(), "%d"); $proxy->java=$ar[0]; $proxy->p=$this->p; return $proxy;} function toString() {$this->p->iBeg("", "castToString"); $this->p->val($this); $this->p->iEnd(); return base64_decode($this->p->res());}}

// Test
$i1 = new Java("java.math.BigInteger", "1");
$i2 = new Java("java.math.BigInteger", "2");
$i3 = $i1->add($i2);
echo $i3->toString() . "\n";

?>


The above simple "Java" class assumes that some Java VM has been started on host "127.0.0.1", port "9267". And it cannot handle values larger than 8192 bytes. Therefore the VM Bridge library Java.inc should be used. Scripts should contain the statement

  require_once("...java/Java.inc");