XLII. Java
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 the Java extension.
PHP 4 ext/java 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. Build instructions for ext/java can be
found in php4/ext/java/README.
Example 1. Java Example
<?php
// get instance of Java class java.lang.System in PHP
$system = new Java('java.lang.System');
// demonstrate property access
print 'Java version='.$system->getProperty('java.version').' <br>';
print 'Java vendor=' .$system->getProperty('java.vendor').' <br>';
print 'OS='.$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");
print $formatter->format(new Java('java.util.Date'));
?>
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Example 2. AWT Example
<?php
// This example is only intented 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 cooerced 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.
sapi/servlet builds upon the mechanism defined by ext/java to enable
the entire PHP processor to be run as a servlet. The primary advanatage
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.
