LXVI. PHP / Java Integration
There are two possible ways to bridge PHP and Java: you can either
integrate PHP into a Java Servlet
environment, which is the more stable and efficient solution,
or integrate Java support into PHP. The former is provided by a SAPI
module that interfaces with the Servlet server, the latter by this
Java extension.
The Java extension provides a simple and effective means for creating and
invoking methods on Java objects from PHP. The JVM is created using JNI,
and everything runs in-process.
| Warning | This extension is
EXPERIMENTAL. The behaviour of this extension --
including the names of its functions and anything else documented
about this extension -- may change without notice in a future release of PHP.
Use this extension at your own risk. |
You need a Java VM installed on your machine to use this extension.
This PECL extension
is not bundled with PHP.
In PHP 4 this PECL extensions
source can be found in the ext/ directory within the
PHP source or at the PECL link above.
In order to use these functions you must compile PHP with Java support by
using the --with-java[=DIR] where DIR
points to the base install directory of your JDK. This extension can only
be built as a shared extension. Additional build extensions can be found
in php-src/ext/java/README.
Windows users will enable php_java.dll inside
of php.ini in order to use these functions.
In PHP 4 this DLL resides in
the extensions/ directory within the PHP Windows
binaries download.
You may download this PECL
extension DLL from the
PHP Downloads page or at
http://snaps.php.net/.
Note:
In order to enable this module on a Windows environment with PHP <=
4.0.6, you must make jvm.dll available to your
systems PATH. No additional DLL is needed for PHP versions > 4.0.6.
The behaviour of these functions is affected by settings in php.ini.
Table 1. Java configuration options | Name | Default | Changeable | Changelog |
|---|
| java.class.path | NULL | PHP_INI_ALL | | | java.home | NULL | PHP_INI_ALL | | | java.library.path | NULL | PHP_INI_ALL | | | java.library | JAVALIB | PHP_INI_ALL | |
For further details and definitions of the
PHP_INI_* constants, see the Appendix G.
This extension has no resource types defined. This extension has no constants defined.
Example 1. Java Example
<?php
// get instance of Java class java.lang.System in PHP
$system = new Java('java.lang.System');
// demonstrate property access
echo 'Java version=' . $system->getProperty('java.version') . '<br />';
echo 'Java vendor=' . $system->getProperty('java.vendor') . '<br />';
echo 'OS=' . $system->getProperty('os.name') . ' ' .
$system->getProperty('os.version') . ' on ' .
$system->getProperty('os.arch') . ' <br />';
// java.util.Date example
$formatter = new Java('java.text.SimpleDateFormat',
"EEEE, MMMM dd, yyyy 'at' h:mm:ss a zzzz");
echo $formatter->format(new Java('java.util.Date'));
?>
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Example 2. AWT Example
<?php
// This example is only intended to be run as a CGI.
$frame = new Java('java.awt.Frame', 'PHP');
$button = new Java('java.awt.Button', 'Hello Java World!');
$frame->add('North', $button);
$frame->validate();
$frame->pack();
$frame->visible = True;
$thread = new Java('java.lang.Thread');
$thread->sleep(10000);
$frame->dispose();
?>
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Notes:
new Java() will create an instance of a class if
a suitable constructor is available. If no parameters are passed and
the default constructor is useful as it provides access to classes
like java.lang.System which expose most of their
functionallity through static methods.
Accessing a member of an instance will first look for bean properties
then public fields. In other words, print $date.time
will first attempt to be resolved as $date.getTime(),
then as $date.time.
Both static and instance members can be accessed on an object with
the same syntax. Furthermore, if the java object is of type
java.lang.Class, then static members of the class
(fields and methods) can be accessed.
Exceptions raised result in PHP warnings, and NULL results. The
warnings may be eliminated by prefixing the method call with an
"@" sign. The following APIs may be used to retrieve and reset
the last error:
Overload resolution is in general a hard problem given the
differences in types between the two languages. The PHP Java
extension employs a simple, but fairly effective, metric for
determining which overload is the best match.
Additionally, method names in PHP are not case sensitive, potentially
increasing the number of overloads to select from.
Once a method is selected, the parameters are coerced if necessary,
possibly with a loss of data (example: double precision floating point
numbers will be converted to boolean).
In the tradition of PHP, arrays and hashtables may pretty much
be used interchangably. Note that hashtables in PHP may only be
indexed by integers or strings; and that arrays of primitive types
in Java can not be sparse. Also note that these constructs are
passed by value, so may be expensive in terms of memory and time.
The Java Servlet SAPI builds upon the mechanism defined by the Java
extension to enable the entire PHP processor to be run as a servlet.
The primary advantage of this from a PHP perspective is that web servers
which support servlets typically take great care in pooling and reusing
JVMs. Build instructions for the Servlet SAPI module can be found in
php4/sapi/README.
Notes:
While this code is intended to be able to run on any servlet engine,
it has only been tested on Apache's Jakarta/tomcat to date. Bug
reports, success stories and/or patches required to get this code
to run on other engines would be appreciated.
PHP has a habit of changing the working directory. sapi/servlet will
eventually change it back, but while PHP is running the servlet engine
may not be able to load any classes from the CLASSPATH which are
specified using a relative directory syntax, or find the work directory
used for administration and JSP compilation tasks.
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