VM Bridge FAQ

How can I increase the memory available to Java?

Use a VM >= 1.6 and add more RAM to your computer. Older Java versions support the Xmx flag:

java -Xmx512M ... -jar JavaBridge.jar SERVLET:8080

How can I set PHP options?

With a define before a PHP library is loaded. Global options can also be set in the php.ini file. Use phpinfo() to see the location of this file.

How can I configure the bridge?

Useful options which can be set before the Java.inc is loaded are:

define ("JAVA_PREFER_VALUES", false);
define ("JAVA_HOSTS", "127.0.0.1:8080");
require_once ("java/Java.inc");
...

Server-side options can be set in the php.java.bridge.global.properties file, see the JavaBridge.jar zip file (contained in the JavaBridge.war zip file) for details.

Can I use Java libraries without installing java?

Yes. On a GNU operating system (e.g.: GNU/Linux, GNU/windows (aka "cygwin"), ...) you can use the GCC compiler to compile Java classes to native code. Simply compile the C based extension and omit the --with-java= configure option. The bridge will use the libgcj library, which is part of the GNU gcc compiler. This library also uses much less system resources (memory, files) than a "real" Java VM.

GCJ support has been removed in PHP/Java Bridge version 6. If you want to compile JavaBridge.jar to native code, please use PHP/Java Bridge version 5.5.4 instead.

I can't load the resource or file from the current working directory!?!

The "current working directory" is not useful, as the Java back end may be running on a different server or from a different working directory. Use a full path or a URL resource instead.

I get a blank page or some other error!?!

Check the PHP error log, see your php.ini file for details. If the command:

echo '<?php require_once("http://localhost:8080/JavaBridge/java/Java.inc"); echo java("java.lang.System")->getProperties();?>' | php -n -d allow_url_include=On

Can I use Python instead of PHP?

Yes, see the examples folder from the source download.

Can I access Mono or .NET libraries using the pure PHP implementation?

Yes, PHP/Java Bridge version < 6 contains a PHP library "Mono.inc" generated from "Java.inc" and a "MonoBridge.exe" generated from "JavaBridge.jar". If you want to compile from source, use the configure option --with-mono.

Mono/.NET support has been removed in PHP/Java Bridge version 6. If you want to access Mono/.NET libraries, please use PHP/Java Bridge version 5.5.4 instead.

What does a "protocol error ..." mean?

That your Java has problems, for example an OutOfMemoryError. Check the back end (Tomcat/J2EE/...) log for details.

It could also indicate a setup problem. If you use a servlet back end but haven't set the java.servlet or JAVA_SERVLET option, the PHP library Java.inc will confuse the HTML response from the servlet engine with the XML protocol used by the bridge.

Does it support PHP 4?

Start a simple socket listener and use the following "Java" class:

<?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. Then type: php sample.php
//
class P{var$Pc="<C v=\"%s\" p=\"I\">",$PC="</C>",$Pi="<I v=\"%d\" m=\"%s\" p=\"I\">",$PI="</I>",$Ps="<S v=\"%s\"/>",$Pl="<L v=\"%d\" p=\"%s\"/>",$Po="<O v=\"%d\"/>",$c;function str($s){fwrite($this->c,sprintf($this->Ps,$s));}function obj($s){fwrite($this->c,sprintf($this->Po,$s->j));}function P(){$this->c=fsockopen("127.0.0.1",9267);}function cB($s){fwrite($this->c,sprintf($this->Pc,$s));}function cE(){fwrite($this->c,$this->PC);}function iB($o,$m){fwrite($this->c,sprintf($this->Pi,$o,$m));}function iE(){fwrite($this->c,$this->PI);}function v($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$j,$p;function Java(){if(!func_num_args())return;$this->p=gP();$ar=func_get_args();$this->p->cB(array_shift($ar));foreach($ar as$arg)$this->p->v($arg);$this->p->cE();$ar=sscanf($this->p->res(),"%d");$this->j=$ar[0];}function __call($m,$a,&$rv){$this->p->iB($this->j,$m);foreach($a as$arg)$this->p->v($arg);$this->p->iE();$p=new Java();$ar=sscanf($this->p->res(),"%d");$p->j=$ar[0];$p->p=$this->p;$rv=$p;return true;}function toString(){$this->p->iB("","castToString");$this->p->v($this);$this->p->iE();return base64_decode($this->p->res());}}overload("Java");


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


Class loading questions

Why has java_require() been deprecated?

Because Java doesn't have a module system.

For example a library "lucene-2.3.1.jar" required by application B, cannot be loaded if an older version of the library, required by application A, is already cached.
An attempt to link the library anyway will cause "NoClassDefFound" or "NoSuchMethod" errors at runtime. Or some procedures may throw checked exceptions even though they haven't declared them.

To protect PHP developers from Java's "jar hell", I have removed the dynamic class loading mechanism from PHP/Java Bridge version 6.0; java_require() issues a warning.

A proper Java module system must use special Java VM hooks, which don't exist until now.

How do I load Java libraries?

You should link your Java application as described in the Java standalone or Java webapps documents.

Can the VM Bridge load java libraries?

No, it can't. java_require is deprecated and has been removed in PHP/Java Bridge version 6. Ask Java gurus for help.

Where can I store my java libraries for the VM Bridge?

In your web application WEB-INF/lib directory.

If libraries should be available globally, store them in java.ext.dirs, for example in /usr/share/java/ext.

Why do I get a ClassNotFoundException?

You probably haven't loaded 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 your web application WEB-INF/lib directory.

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!

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 the PHP/Java Bridge binary.
2. Copy JavaBridge.jar, php-servlet.jar and php-script.jar from the JavaBridge.war zip archive to $CATALINA_HOME/lib.
3. Add the following 9 lines marked with a + to the tomcat $CATALINA_HOME/conf/web.xml web app:

   
<web-app xmlns=... >

+ <listener><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.fastcgi.FastCGIServlet</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>
...

</web-app>

4. Start tomcat.

<?php echo java("java.lang.System")->getProperties(); ?>

In case you don't need to access Java from all of your scripts, you can set the php_include_java option to Off and require_once("java/Java.inc"), if needed.

How do I create a standalone PHP web application for distribution and how can users deploy it into tomcat?

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.fastcgi.FastCGIServlet</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>


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, or a FCGI server. 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.

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 = java("DocumentHome");
$PortableRemoteObject = java("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


static final javax.script.CompiledScript script =((javax.script.Compilable)(new javax.script.ScriptEngineManager().getEngineByName("php"))).compile("<?php echo 'Hello '.java_context()->get('hello').'!'; ?>");
...
javax.script.CompiledScript instance = (javax.script.CompiledScript)((java.security.cert.CertStoreParameters)script).clone();
instance.getEngine().setContext(new php.java.script.servlet.PhpHttpScriptContext(instance.getEngine().getContext(),this,application,request,response));



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

General runtime questions

How do I include a local (*.asp, *.jsp, ...) resource?

Use the virtual() or java_virtual() function.

Warning: Do not open a "loop back" url connection (e.g. via fopen("http://localhost.../foo.asp")) to include the local resource. This might exceed the HTTP server's pool size and create a deadlock!

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 = java("java.lang.Byte");
$byte = $Byte->TYPE;
$Array = java("java.lang.reflect.Array");
$byteArray = $Array->newInstance($byte, 255);
$System = java("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 1.5 GHZ x86 cpu running RedHat Fedora 10 Linux and Sun jdk1.6.0_02. We have tested "Mozilla Rhino" 1.6 release 2 from JDK 1.6, Caucho "Quercus" version 3.2.1, the PHP/Java Bridge version 5.4.4, and PHP 4's ext/java.

<?php
$buf=new java("java.lang.StringBuilder");
for ($i=0; $i<400000; $i++) $buf->append($i);
echo $buf->length() . "\n";
?>

<?php
$buf=new java("java.lang.StringBuilder");
for ($i=0; $i<400000; $i++) $buf->append(new java("java.lang.String", $i));
echo $buf->length() . "\n";
?>

buf = new java.lang.StringBuilder();
for(i=0; i<400000; i++) buf.append(new java.lang.Integer(i));
print (buf.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.

In PHP 5.3 or above the following code can be used:

use java\lang\String as JString;

class String extends JString {
  function toString(){return "I am " . parent::toString();}
  function __toString() {return $this->toString();}
}

echo new String("foo");

=> I am foo

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

With java_values(). For example:

  $ar = java("java.lang.reflect.Array")->newInstance(java("java.lang.Integer"), 2);
  $ar[0] = new java("java.lang.Integer", 2);$ar[1] = new java("java.lang.Integer", 5);
  print_r(java_values($ar));


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

With java_closure(ENV, MAP, INTERFACES). For example:

  class Foo {
   function toString() {return "php::foo";}
  }
  $foo = new Foo();
  $jObj = java_closure($foo);
  $String = 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");
$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");
$t1 = new java('Varargs$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.Then type: php sample.php
//
class P{var$Pc="<C v=\"%s\" p=\"I\">",$PC="</C>",$Pi="<I v=\"%d\" m=\"%s\" p=\"I\">",$PI="</I>",$Ps="<S v=\"%s\"/>",$Pl="<L v=\"%d\" p=\"%s\"/>",$Po="<O v=\"%d\"/>",$c;function str($s){fwrite($this->c,sprintf($this->Ps,$s));}function obj($s){fwrite($this->c,sprintf($this->Po,$s->j));}function P(){$this->c=fsockopen("127.0.0.1",9267);}function cB($s){fwrite($this->c,sprintf($this->Pc,$s));}function cE(){fwrite($this->c,$this->PC);}function iB($o,$m){fwrite($this->c,sprintf($this->Pi,$o,$m));}function iE(){fwrite($this->c,$this->PI);}function v($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$j,$p;function Java(){if(!func_num_args())return;$this->p=gP();$ar=func_get_args();$this->p->cB(array_shift($ar));foreach($ar as$arg)$this->p->v($arg);$this->p->cE();$ar=sscanf($this->p->res(),"%d");$this->j=$ar[0];}function __call($m,$a){$this->p->iB($this->j,$m);foreach($a as$arg)$this->p->v($arg);$this->p->iE();$p=new Java();$ar=sscanf($this->p->res(),"%d");$p->j=$ar[0];$p->p=$this->p;return$p;}function toString(){$this->p->iB("","castToString");$this->p->v($this);$this->p->iE();return base64_decode($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");

What does "The requested method PUT is not allowed ... at localhost Port 80" mean?

It means that request.getServerPort() is lying. Port 80 is privileged and therefore cannot be the servlet engine's server port.

If you use the AJP connector, for example via ProxyPassMatch ^(/.*\.jsp)$ ajp://127.0.0.1$1, set the correct proxyPort in tomcat/conf/server.xml. Example:

<!-- Define an AJP 1.3 Connector on port 8009 -->
- <Connector port="8009" protocol="AJP/1.3" redirectPort="8443" />
+ <Connector port="8009" protocol="AJP/1.3" proxyPort="8080" redirectPort="8443" />