PHP / Java Integration

Introduction

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.

Requirements

You need a Java VM installed on your machine to use this extension.

Installation

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. The DLL for this PECL extension may be downloaded from either the » PHP Downloads page or from » http://pecl4win.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.

This extension has no resource types defined.

Predefined Constants

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’));
?>

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();
?>

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:

  • java_last_exception_get()
  • java_last_exception_clear()
• 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.

Java Servlet SAPI

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.

Table of Contents

• java_last_exception_clear — Clear last Java exception
• java_last_exception_get — Get last Java exception

PHP6 Unofficial Changelog

You may also want to read the Unofficial PHP 6 Changelog.

If you want to make use of PHP 6 when it comes, you’re going to have to write your new scripts so they are compatible, and possibly change some of your existing scripts. To start making your scripts PHP 6 compatible, I’ve compiled a list of tips to follow when scripting:

1. Don’t use register_globals. In PHP 6, support for register_globals will be no more. There will be no option to turn it on or off - it will not exist. This change should not affect you, as you shouldn’t really use register_globals anyway. If you don’t already know, register_globals puts $_REQUEST into the global scope, so you can access the variables just like any other variable. Instead, you should access inputed data like this:
   

   $_GET['input'];
   $_POST['input'];
   $_REQUEST['input'];

1. Stop using magic_quotes. In my opinion, this tip should be applied whether you are using PHP 3, 4 or 5. Thankfully, in PHP 6, the magic_quotes feature is going to dissapear with register_globals. For those who don’t know, magic_quotes automically escapes single quotes, double quotes, backslashes, and NULL characters.
2. Don’t Register Long Arrays. If you access user inputted data using $HTTP_POST_VARS or $HTTP_GET_VAR, you better stop now. Instead, you should use the superglobals - $_SERVER, $_COOKIE, $_GET, $_POST, $_FILES…
3. preg instead or ereg. If you’re using ereg functions for regular expression tasks, then you should start using the preg functions instead. ereg will not be available in the PHP core as of version 6.
4. Don’t initiate objects with the reference operator. If you’re initiating objects using the reference operator, you should stop now. It will generate an E_STRICT error.
   

   $a = & new object(); // Do not do
   $a = new object(); // Do this as of PHP 6

Opensource PHP framework Symfony

Symfony based on the best practices of web development, thoroughly tried on several active websites, symfony aims to speed up the creation and maintenance of web applications, and to replace the repetitive coding tasks by power, control and pleasure.

Symfony provides a lot of features seamlessly integrated together, such as:

• simple templating and helpers
• cache management
• smart URLs
• scaffolding
• multilingualism and I18N support
• object model and MVC separation
• Ajax support
• enterprise ready

Do you want to know more? Get started and join the growing symfony community now!

More Details 

Difference Between PHP4 & PHP5

Here’s a quick overview of what has changed between PHP4 and PHP5. PHP5 for the most part is backwards compatible with PHP4, but there are a couple key changes that might break your PHP4 script in a PHP5 environment. If you aren’t already, I stronly suggest you start developing for PHP5. Many hosts these days offer a PHP5 environment, or a dual PHP4/PHP5 setup so you should be fine on that end. Using all of these new features is worth even a moderate amount of trouble you might go through finding a new host!

Note: Some of the features listed below are only in PHP5.2 and above.

Object Model
The new OOP features in PHP5 is probably the one thing that everyone knows for sure about. Out of all the new features, these are the ones that are talked about most!

Passed by Reference
This is an important change. In PHP4, everything was passed by value, including objects. This has changed in PHP5 — all objects are now passed by reference.

PHP Code:

$joe = new Person();
$joe->sex = ‘male’; $betty = $joe;
$betty->sex = ‘female’;echo $joe->sex; // Will be ‘female’
The above code fragment was common in PHP4. If you needed to duplicate an object, you simply copied it by assigning it to another variable. But in PHP5 you must use the new clone keyword.Note that this also means you can stop using the reference operator (&). It was common practice to pass your objects around using the & operator to get around the annoying pass-by-value functionality in PHP4.

Class Constants and Static Methods/Properties
You can now create class constants that act much the same was as define()’ed constants, but are contained within a class definition and accessed with the :: operator.

Static methods and properties are also available. When you declare a class member as static, then it makes that member accessible (through the :: operator) without an instance. (Note this means within methods, the $this variable is not available)

Visibility
Class methods and properties now have visibility. PHP has 3 levels of visibility:

1. Public is the most visible, making methods accessible to everyone and properties readable and writable by everyone.
2. Protected makes members accessible to the class itself and any subclasses as well as any parent classes.
3. Private makes members only available to the class itself.

Unified Constructors and Destructors
PHP5 introduces a new unified constructor/destructor names. In PHP4, a constructor was simply a method that had the same name as the class itself. This caused some headaches since if you changed the name of the class, you would have to go through and change every occurrence of that name.

In PHP5, all constructors are named __construct(). That is, the word construct prefixed by two underscores. Other then this name change, a constructor works the same way.

Also, the newly added __destruct() (destruct prefixed by two underscores) allows you to write code that will be executed when the object is destroyed.

Abstract Classes
PHP5 lets you declare a class as abstract. An abstract class cannot itself be instantiated, it is purely used to define a model where other classes extend. You must declare a class abstract if it contains any abstract methods. Any methods marked as abstract must be defined within any classes that extend the class. Note that you can also include full method definitions within an abstract class along with any abstract methods.

Interfaces
PHP5 introduces interfaces to help you design common APIs. An interface defines the methods a class must implement. Note that all the methods defined in an interface must be public. An interface is not designed as a blueprint for classes, but just a way to standardize a common API.

The one big advantage to using interfaces is that a class can implement any number of them. You can still only extend on parent class, but you can implement an unlimited number of interfaces.

Magic Methods
There are a number of “magic methods” that add an assortment to functionality to your classes. Note that PHP reserves the naming of methods prefixed with a double-underscore. Never name any of your methods with this naming scheme!

Some magic methods to take note of are __call, __get, __set and __toString. These are the ones I find most useful.

Finality
You can now use the final keyword to indicate that a method cannot be overridden by a child. You can also declare an entire class as final which prevents it from having any children at all.

The __autoload Function
Using a specially named function, __autoload (there’s that double-underscore again!), you can automatically load object files when PHP encounters a class that hasn’t been defined yet. Instead of large chunks of include’s at the top of your scripts, you can define a simple autoload function to include them automatically.

PHP Code:

function __autoload($class_name) {
require_once “./includes/classes/$class_name.inc.php”;
}


Note you can change the autoload function or even add multiple autoload functions using spl_autoload_register and related functions.

Standard PHP Library
PHP now includes a bunch of functionality to solve common problems in the so-named SPL. There’s a lot of cool stuff in there, check it out!

For example, we can finally create classes that can be accessed like arrays by implementing the ArrayAccess interface. If we implement the Iterator interface, we can even let our classes work in situations like the foreach construct.

Miscellaneous Features

Type Hinting
PHP5 introduces limited type hinting. This means you can enforce what kind of variables are passed to functions or class methods. The drawback is that (at this time), it will only work for classes or arrays — so no other scalar types like integers or strings.

To add a type hint to a parameter, you specify the name of the class before the $. Beware that when you specify a class name, the type will be satisfied with all of its subclasses as well.

PHP Code:

function echo_user(User $user) {
echo $user->getUsername();
}


If the passed parameter is not User (or a subclass of User), then PHP will throw a fatal error.

Exceptions
PHP finally introduces exceptions! An exception is basically an error. By using an exception however, you gain more control the simple trigger_error notices we were stuck with before.

An exception is just an object. When an error occurs, you throw an exception. When an exception is thrown, the rest of the PHP code following will not be executed. When you are about to perform something “risky”, surround your code with a try block. If an exception is thrown, then your following catch block is there to intercept the error and handle it accordingly. If there is no catch block, a fatal error occurs.

PHP Code:

try {
$cache->write();
} catch (AccessDeniedException $e) {
die(‘Could not write the cache, access denied.’);
} catch (Exception $e) {
die(‘An unknown error occurred: ‘ . $e->getMessage());
}


E_STRICT Error Level
There is a new error level defined as E_STRICT (value 2048). It is not included in E_ALL, if you wish to use this new level you must specify it explicitly. E_STRICT will notify you when you use depreciated code. I suggest you enable this level so you can always stay on top of things.

Foreach Construct and By-Reference Value
The foreach construct now lets you define the ‘value’ as a reference instead of a copy. Though I would suggest against using this feature, as it can cause some problems if you aren’t careful:

PHP Code:

foreach($array as $k => &$v) {
// Nice and easy, no working with $array[$k] anymore
$v = htmlentities($v);
} // But be careful, this will have an unexpected result because
// $v will still be a reference to the last element of the $array array
foreach($another_array as $k => $v) {}
New Functions
PHP5 introduces a slew of new functions. You can get a list of them from the PHP Manual.New Extensions
PHP5 also introduces new default extensions.

• SimpleXML for easy processing of XML data
• DOM and XSL extensions are available for a much improved XML-consuming experience. A breath of fresh air after using DOMXML for PHP4!
• PDO for working with databases. An excellent OO interface for interacting with your database.
• Hash gives you access to a ton of hash functions if you need more then the usual md5 or sha1.

Compatibility Issues
The PHP manual has a list of changes that will affect backwards compatibility. You should definately read through that page, but here is are three issues I have found particularly tiresome:

• array_merge() will now give you warnings if any of the parameters are not arrays. In PHP4, you could get away with merging non-arrays with arrays (and the items would just be added if they were say, a string). Of course it was bad practice to do this to being with, but it can cause headaches if you don’t know about it.
• As discussed above, objects are now passed by references. If you want to copy a object, make sure to use the clone keyword.
• get_*() now return names as they were defined. If a class was called MyTestClass, then get_class() will return that — case sensitive! In PHP4, they were always returned in lowercase.