NAME

Inline::Java - Write Perl classes in Java.

SYNOPSIS

   use Inline Java => <<'END_OF_JAVA_CODE' ;
      class Pod_alu {
         public Pod_alu(){
         }

         public int add(int i, int j){
            return i + j ;
         }

         public int subtract(int i, int j){
            return i - j ;
         }
      }   
   END_OF_JAVA_CODE

   my $alu = new Pod_alu() ;
   print($alu->add(9, 16) . "\n") ; # prints 25
   print($alu->subtract(9, 16) . "\n") ; # prints -7

WARNING

THIS IS ALPHA SOFTWARE. It is incomplete and possibly unreliable. It is also possible that some elements of the interface (API) will change in future releases.

DESCRIPTION

The Inline::Java module allows you to put Java source code directly "inline" in a Perl script or module. A Java compiler is launched and the Java code is compiled. Then Perl asks the Java classes what public methods have been defined. These classes and methods are available to the Perl program as if they had been written in Perl.

The process of interrogating the Java classes for public methods occurs the first time you run your Java code. The namespace is cached, and subsequent calls use the cached version.

USING THE Inline::Java MODULE

Inline::Java is driven by fundamentally the same idea as other Inline language modules, like Inline::C or Inline::CPP. Because Java is both compiled and interpreted, the method of getting your code is different, but overall, using Inline::Java is very similar to any other Inline language module.

This section will explain the different ways to use Inline::Java. For more details on Inline, see 'perldoc Inline'.

Basic Usage

The most basic form for using Inline::Java is:

   use Inline Java => 'Java source code' ;

Of course, you can use Perl's "here document" style of quoting to make the code slightly easier to read:

   use Inline Java => <<'END';

      Java source code goes here.

   END

The source code can also be specified as a filename, a subroutine reference (sub routine should return source code), or an array reference (array contains lines of source code). This information is detailed in 'perldoc Inline'.

In order for Inline::Java to function properly, it needs to know where to find the Java compiler (javac) and the Java Runtime (java) on your machine. This is done using one of the following techniques:

   - set the BIN configuration option to the correct directory
   - set the PERL_INLINE_JAVA_BIN environment variable to the correct 
     directory
   - put the correct directory in your PATH environment variable

CONFIGURATION OPTIONS

There are a number of configuration options that dictate the behavior of Inline::Java:

   BIN: 
      Specifies the path to your Java binaries. 
          Ex: BIN => 'my/java/bin/path'
      Note: This configuration option only has an effect on the first
      'use Inline Java' call inside a Perl script, since all other calls 
      make use of the same JVM. However, you can use it if you want to 
      change which 'javac' executable is used for subsequent calls.

   PORT:
      Specifies the starting port number for the server. If many 
      C<Inline::Java> blocks are declared, the port number is 
      incremented each time.    
      Default is 7890.
      Ex: PORT => 4567
      Note: This configuration option only has an effect on the first
      'use Inline Java' call inside a Perl script, since all other calls 
      make use of the same JVM.

   STARTUP_DELAY:
      Specifies the maximum number of seconds that the Perl script
      will try to connect to the Java server. In other this is the
      delay that Perl gives to the Java server to start.
      Default is 15 seconds.
      Ex: STARTUP_DELAY => 20
      Note: This configuration option only has an effect on the first
      'use Inline Java' call inside a Perl script, since all other calls 
      make use of the same JVM.

   CLASSPATH:
      Adds the specified CLASSPATH to the environment CLASSPATH.
      Ex: CLASSPATH => '/my/other/java/classses'
      Note: This configuration option only has an effect on the first
      'use Inline Java' call inside a Perl script, since all other calls 
      make use of the same JVM.

   JNI:
      Toggles the execution mode. The default is to use the client/server
      mode. To use the JNI extension (you must have built it at install 
      time though. See README and README.JNI for more information), set 
      JNI to 1. 
      Ex: JNI => 1
      Note: This can also be set globally by setting the 
      PERL_INLINE_JAVA_JNI environment variable to 1.
      Note: This configuration option only has an effect on the first
      'use Inline Java' call inside a Perl script, since all other calls 
      make use of the same JVM.

   SHARED_JVM:
      This mode enables mutiple processes to share the same JVM. It was 
      created mainly in order to be able to use C<Inline::Java> under 
      mod_perl. 
      Ex: SHARED_JVM => 1
      Note: This configuration option only has an effect on the first
      'use Inline Java' call inside a Perl script, since all other calls 
      make use of the same JVM.

   DEBUG:
      Enables debugging info
      Ex: DEBUG => 1

   WARN_METHOD_SELECT:
      Throws a warning when C<Inline::Java> has to 'choose' between 
      different method signatures. The warning states the possible 
      choices and the signature chosen.
      Ex: WARN_METHOD_SELECT => 1

   STUDY:
      Takes an array of Java classes that you wish to have 
      C<Inline::Java> learn about so that you can use them inside Perl.
      Ex: STUDY => ['java.lang.HashMap', 'my.class'] ;

   AUTOSTUDY:
      Makes C<Inline::Java> automatically study unknown classes it 
      encounters.
      Ex: STUDY => ['java.lang.HashMap', 'my.class'] ;

ENVIRONMENT VARIABLES

   PERL_INLINE_JAVA_BIN:
      Same as the BIN option.

   PERL_INLINE_JAVA_JNI:
      Same as the JNI option.

   PERL_INLINE_SHARED_JVM:
      Same as the SHARED_JVM option.

   PERL_INLINE_JAVA_DEBUG:
      Same as the DEBUG option.

   PERL_INLINE_JAVA_COMMAND_COM:
      If set to a true value, tells Inline::Java that you are using 
      the command.com shell. Inline::Java should normally be able
      to determine this on its own.

CLASSES AND OBJECTS

Because Java is object oriented, any interface between Perl and Java needs to support Java classes adequately.

Example:

   use Inline Java => <<'END' ;
      class Pod_1 {
         String data = "data" ;
         static String sdata = "static data" ;

         public Pod_1(){
         }

         public String get_data(){
            return data ;
         }

         public static String get_static_data(){
            return sdata ;
         }

         public void set_data(String d){
            data = d ;
         }

         private void priv(){
         }
      }
   END

   my $obj = new Pod_1 ;
   print($obj->get_data() . "\n") ; # prints data
   $obj->set_data("new data") ;
   print($obj->get_data() . "\n") ; # prints new data

Inline::Java created a new namespace called main::Pod_1 and created the following functions:

   sub main::Pod_::new { ... }
   sub main::Pod_::Pod_1 { ... }
   sub main::Pod_::get_data { ... }
   sub main::Pod_::get_sdata { ... }
   sub main::Pod_::set_data { ... }
   sub main::Pod_::DESTROY { ... }

Note that only the public methods are exported to Perl. Note also that the class itself is not public. With Inline::Java you cannot create public classes because Java requires that they be defined in a .java file of the same name (Inline::Java can't work this way).

Inner classes are also supported, you simply need to supply a reference to an outer class object as the first parameter of the constructor:

   use Inline Java => <<'END' ;
      class Pod_2 {
         public Pod_2(){
         }

         public class Pod_2_Inner {
            public String name = "Pod_2_Inner" ;

            public Pod_2_Inner(){
            }
         }
      }
   END

   my $obj = new Pod_2() ;
   my $obj2 = new Pod_2::Pod_2_Inner($obj) ;
   print($obj2->{name} . "\n") ; # prints Pod_2_Inner

METHODS

In the previous example we have seen how to call a method. You can also call static methods in the following manner:

   print Pod_1->get_sdata() . "\n" ; # prints static data
   # or
   my $obj = new Pod_1() ;
   print $obj->get_sdata() . "\n" ; # prints static data

You can pass any kind of Perl scalar or any Java object to a method. It will be automatically converted to the correct type:

   use Inline Java => <<'END' ;
      class Pod_3_arg {
         public Pod_3_arg(){
         }
      }
      class Pod_3 {
         public int n ;

         public Pod_3(int i, String j, Pod_3_arg k) {
            n = i ;
         }
      }
   END

   my $obj = new Pod_3_arg() ;
   my $obj2 = new Pod_3(5, "toto", $obj) ;
   print($obj2->{n} . "\n") ; # prints 5

will work fine. These objects can be of any type, even if these types are not known to Inline::Java. This is also true for return types:

   use Inline Java => <<'END' ;
      import java.util.* ;

      class Pod_4 {
         public Pod_4(){
         }

         public HashMap get_hash(){
            HashMap h = new HashMap() ;
            h.put("key", "value") ;

            return h ;
         }

         public String do_stuff_to_hash(HashMap h){
           return (String)h.get("key") ;
         }
      }
   END

   my $obj = new Pod_4() ;
   my $h = $obj->get_hash() ;
   print($obj->do_stuff_to_hash($h) . "\n") ; # prints value

Objects of types unknown to Perl can exist in the Perl space, you just can't call any of their methods.

MEMBER VARIABLES

You can also access all public member variables (static or not) from Perl. As with method arguments, the types of these variables does not need to be known to Perl:

   use Inline Java => <<'END' ;
      import java.util.* ;

      class Pod_5 {
         public int i ;
         public static HashMap hm ;

         public Pod_5(){
         }
     }
   END

   my $obj = new Pod_5() ;
   $obj->{i} = 2 ;
   print($obj->{i} . "\n") ; # prints 2
   my $hm1 = $obj->{hm} ; # instance way
   my $hm2 = $Pod_4::hm ; # static way

Note: Watch out for typos when accessing members in the static fashion, 'use strict' will not catch them since they have a package name...

ARRAYS

You can also send and receive arrays. This is done simply by using Perl lists:

   use Inline Java => <<'END' ;
      import java.util.* ;

      class Pod_6 {
         public int i[] = {5, 6, 7} ;

         public Pod_6(){
         }

         public String [] f(String a[]){
            return a ;
         }

         public String [][] f(String a[][]){
            return a ;
         }
     }
   END

   my $obj = new Pod_6() ;
   my $i_2 = $obj->{i}->[2] ; # 7
   print($i_2 . "\n") ; # prints 7

   my $a1 = $obj->f(["a", "b", "c"]) ; # String []
   my $a2 = $obj->f([
      ["00", "01"],
      ["10", "11"],
   ]) ; # String [][]
   print($a2->[1]->[0] . "\n") ; # prints 10

TYPE CASTING

Sometimes when a class as many signatures for the same method, Inline::Java will have to select one of the signatures based on the arguments that are passed:

   use Inline Java => <<'END' ;
      class Pod_7 {
         public Pod_7(){
         }

         public String f(int i){
            return "int" ;
         }

         public String f(char c){
            return "char" ;
         }
      }
   END

   my $obj = new Pod_7() ;
   print($obj->f('5') . "\n") ; # prints int

In this case, Inline::Java will call f(int i), because '5' is an integer. But '5' is a valid char as well. So to force the call of f(char c), do the following:

   use Inline::Java qw(cast) ;
   $obj->f(cast('char', '5')) ;
   # or
   $obj->f(Inline::Java::cast('char', '5')) ;

The cast function forces the selection of the matching signature. Note that the cast must match the argument type exactly. Casting to a class that extends the argument type will not work.

Another case where type casting is need is when one wants to pass an array as a java.lang.Object:

   use Inline Java => <<'END';
      class Pod_8 {
         public Object o ;
         int a[] = {1, 2, 3} ;

         public Pod_8() {
         }
      }
   END

   my $obj = new Pod_8() ;
   $obj->{o} = [1, 2, 3] ;      # No!

The reason why this will not work is simple. When Inline::Java sees an array, it checks the Java type you are trying to match it against to validate the construction of your Perl list. But in this case, it can't validate the array because you're assigning it to an Object. You must use the 3 parameter version of the cast function to do this:

   $obj->{o} = Inline::Java::cast(
     "java.lang.Object", 
     [1, 2, 3],
     "[Ljava.lang.String;") ;

This tells Inline::Java to validate your Perl list as a String [], and then cast it as an Object.

Here is how to construct the array type representations:

  [<type>  -> 1 dimensional <type> array
  [[<type> -> 2 dimensional <type> array
  ...

  where <type> is one of:
    B byte     S short     I int     J long  
    F float    D double    C char    Z boolean

    L<class>; array of <class> objects

This is described in more detail in most Java books that talk about reflection.

But you only need to do this if you have a Perl list. If you already have a Java array reference obtained from elsewhere, you don't even need to cast:

   $obj->{o} = $obj->{a} ;

EXCEPTIONS

You can now (as of 0.31) catch exceptions as objects when they are thrown from Java. To do this you use the regular Perl exception tools: eval and $@. A helper function named 'caught' is provided to help determine the type of the exception. Here is a example of a typical use:

   use Inline Java => <<'END' ;
      import java.util.* ;

      class Pod_9 {
         public Pod_9(boolean t) throws Exception {
                        if (t){
               throw new Exception("ouch!") ;
                        }
         }
      }
   END

   use Inline::Java qw(caught) ;

   eval {
           my $obj = new Pod_9(1) ;
   } ;
   if ($@){
      if (caught("java.lang.Exception")){
         my $msg = $@->getMessage() ;
         print($msg . "\n") ; # prints ouch!
      }
      else{
         # It wasn't a Java exception after all...
         die $@ ;
      }
   }

What's important to understand is that $@ actually contains a reference to the Throwable object that was thrown by Java. The getMessage() function is really a method of the java.lang.Exception class. So if Java is throwing an custom exception you have in your code, you will have access to that exception object's public method just like any other Java object in Inlin::Java. It is also probably a good idea to undef $@ once you have treated a Java exception, or else the object still has a reference until $@ is reset by the next eval.

CALLBACKS

You can now (as of 0.31), call Perl functions from Java. To do this you need to create an InlinePerlJavaCaller object. You can then use the CallPerl method to call your Perl function. You pass the parameters using an array of java.lang.Object. The method will return the result in a java.lang.Object, which you must then cast to as a java.lang.String (if your Perl method returns a Perl scalar), or anything else if your Perl function returns an "Inline::Java" object. Here is a example of a typical use:

   use Inline Java => <<'END' ;
      import java.util.* ;

      class Pod_regexp extends InlineJavaPerlCaller {
         public Pod_regexp(){
         }

         public boolean match(String target, String pattern)
            throws InlineJavaException {
            try {
               String m = (String)CallPerl("main", "regexp", 
                  new Object [] {target, pattern}) ;

               if (m.equals("1")){
                  return true ;
               }
            }
            catch (PerlException pe){
               // $@ is in pe.GetObject()
            }

            return false ;
         }
      }
   END

   my $re = new Pod_regexp() ;
   my $match = $re->match("Inline::Java", "^Inline") ;
   print($match . "\n") ; # prints 1

        
   sub regexp { 
      my $target = shift ;
      my $pattern = shift ;

      return ($target =~ /$pattern/) ;
   }

The CallPerl method can throw 2 types of exceptions, both of which are inner classes of InlineJavaPerlCaller: InlineJavaException and PerlException. The former, which designates an internal Inline::Java error, should never be dealt with and should be thrown back all the way up to the function that was initially called by Perl. The latter indicates that the Perl callback threw an exception (die() or croak()). The value of $@ (this can be a scalar or any valid "Inline::Java" object) can retreived using the GetObject method of the PerlException object.

STUDYING

As of version 0.21, Inline::Java can learn about other Java classes and use them just like the Java code you write inside your Perl script. In fact you are not even required to write Java code inside your Perl script anymore. Here's how to use the 'studying' function:

   use Inline (
      Java => 'STUDY',
      STUDY => ['java.util.HashMap'],
   ) ;

   my $hm = new java::util::HashMap() ;
   $hm->put("key", "value") ;
   my $val = $hm->get("key") ;
   print($val . "\n") ; # prints value

If you do not wish to put any Java code inside you Perl script, you must use the string 'STUDY' as your code. This will skip the build section.

You can also use the AUTOSTUDY option to tell Inline::Java that you wish to study all classes that it comes across:

   use Inline Java => <<'END', AUTOSTUDY => 1 ;
      import java.util.* ;

      class Pod_10 {
         public Pod_10(){
         }

         public HashMap get_hm(){
            HashMap hm = new HashMap() ;
            return hm ;
         }
      }
   END

   my $obj = new Pod_10() ;
   my $hm = $obj->get_hm() ;
   $hm->put("key", "value") ;
   my $val = $hm->get("key") ;
   print($val . "\n") ; # prints value

In this case Inline::Java intercepts the return value of the get_hm() method, sees that it's of a type that it doesn't know about (java.lang.HashMap), and immediately studies the class. After that call the java::lang::HashMap class is available to use through Perl.

USING MULTIPLE SECTIONS

If you wish to use more than one Inline::Java section in your Perl script, you will need to use the Inline NAME option to name your modules. You can then use a special syntax in your CLASSPATH (either the environment variable or the configuration option) to tell what Inline::Java modules it will need to load at runtime:

   package Pod_Foo ;
   use Inline (
      Java => <<'END_Pod_Foo',
        class Pod_Foo {
           public Pod_Foo(){
           }
        } 
   END_Pod_Foo
      NAME => "Pod_Foo",
      CLASSPATH => "[PERL_INLINE_JAVA=Pod_Foo, Pod_Bar]",
   ) ;

   package Pod_Bar ;
   use Inline (
      Java => <<'END_Pod_Bar',
        class Pod_Bar {
           public Pod_Bar() {
           }
        } 
   END_Pod_Bar
      NAME => "Pod_Bar",
   ) ; 

   package main ;
   my $f = new Pod_Foo::Pod_Foo() ;
   my $b = new Pod_Bar::Pod_Bar() ;

If you set the CLASSPATH via the configuration option, remember to do so in the first Inline::Java section. Also remember that you can't use Java packages with Inline::Java. Your classes must be in the unnamed package.

JNI vs CLIENT/SERVER MODES

Starting in version 0.20, it is possible to use the JNI (Java Native Interface) extension. This enables Inline::Java to load the Java virtual machine as a shared object instead of running it as a stand-alone server. This brings an improvement in performance.

If you have built the JNI extension, you must enable it explicitely by doing one of the following:

   - set the JNI configuration option to 1
   - set the PERL_INLINE_JAVA_JNI environment variable to 1

Note: Inline::Java only creates one virtual machine instance. Therefore you can't use JNI for some sections and client/server for others. The first section determines the execution mode.

See README.JNI for more information about the JNI extension.

SHARED_JVM

Starting with version 0.30, the Inline::Java JVM can now be shared between multiple processes. The first process to start the JVM is considered the JVM owner and will shutdown the JVM on exit. All other processes can connect as needed to the JVM. If any of these other processes where created by forking the parent process, the Inline::Java->reconnect_JVM() function must be called in the child to get a fresh connection to the JVM. Ex:

   use Inline (
      Java => <<'END',
         class Pod_11 {
            public static int i = 0 ;
            public Pod_11(){
               i++ ;
            }
         }
   END
      SHARED_JVM => 1,
   ) ;

   my $nb = 5 ;
   for (my $i = 0 ; $i < $nb ; $i++){
      if (! fork()){
         Inline::Java::reconnect_JVM() ;
         my $f = new Pod_11() ;
         exit ;
      }
   }
   sleep(5) ;

   my $f = new Pod_11() ;
   print($f->{i} . "\n") ; # prints 6

Once this code was run, each of the 6 processes will have created a different instance of the 't' class. Data can be shared between the processes by using static members in the Java code.

If processes not forked off the parent are connecting to the shared JVM, the parent's CLASSPATH must be set properly or else the parent will not see these classes. See USING MULTIPLE SECTIONS for more details.

USING Inline::Java IN A CGI

If you want to use Inline::Java in a CGI script, do the following:

   use CGI ;
   use Inline (
      Java => <<'END',
         class Pod_counter {
            public static int cnt = 0 ;
            public Pod_counter(){
               cnt++ ;
            }
         }
   END
      SHARED_JVM => 1,
   ) ;

   Inline::Java::release_JVM() ;

   my $c = new Pod_counter() ;
   my $q = new CGI() ;
   print 
      $q->start_html() . 
      "This page has been accessed " . $c->{cnt} . " times." .
      $q->end_html() ;

The release_JVM() function simply tells the CGI script that it is no longer responsible for shutting down the JVM. What this does is that the first CGI to execute will start the JVM, but by releasing it the JVM will never be shutdown. Subsequent CGI, since they have the SHARED_JVM option enabled, will try to connect to an already existing JVM before trying to start a new one. Therefore if the JVM happens to crash or is killed, the next CGI that runs will start a new one. The JVM will be killed when Apache is shut down.

USING Inline::Java UNDER MOD_PERL

Here is an example of how to use Inline::Java under mod_perl:

   use Apache::Constants ;
   use Inline (
      Java => <<'END',
         class Pod_counter {
            public static int cnt = 0 ;
            public Pod_counter(){
               cnt++ ;
            }
         }
   END
      SHARED_JVM => 1,
   ) ;

   Inline::Java::release_JVM() ;
   my $c = new Pod_counter() ;

   sub handler {
      my $r = shift ;

      my $q = new CGI ;
      print 
         $q->start_html() . 
         "This page has been accessed " . $c->{cnt} . " times." .
         $q->end_html() ;

      return Apache::Constants::OK() ;
   }

See USING Inline::Java UNDER MOD_PERL for more details about the release_JVM() function.

SUPPORTED PLATFORMS

This is an ALPHA release of Inline::Java. Further testing and expanded support for other operating systems and platforms will be a focus for future releases. It has been tested on:

   - Solaris 2.8            + Perl 5.6.1 + Java SDK 1.2.2
   - Solaris 2.8            + Perl 5.6.1 + Java SDK 1.3.1
   - Linux Redhat 7.1 Intel + Perl 5.6 + Java SDK 1.2.2
   - Linux Redhat 7.1 Intel + Perl 5.6 + Java SDK 1.3.1
   - Windows 2000           + Perl 5.6 + Java SDK 1.2.2
   - Windows 2000           + Perl 5.6 + Java SDK 1.3.0
   - Windows 95             + Perl 5.6 + Java SDK 1.3.1
   - Windows 95             + Perl 5.6 + Java SDK 1.2.2

It likely will work with many other configurations.

HOW IT WORKS

This is how Inline::Java works. Once the user's code is compiled by the javac binary, Inline::Java's own Java code is compiled. This code implements a server (or not if you use the JNI mode) that receives requests from Perl to create objects, call methods, destroy objects, etc. It is also capable of analyzing Java code to extract the public symbols. Once this code is compiled, it is executed to extract the symbols from the Java code.

Once this is done, the user's code information is fetched and is bound to Perl namespaces. Then Inline::Java's code is run to launch the server. The Perl script then connects to the server using a TCP socket (or not if you use the JNI mode). Then each object creation or method invocation on "Java objects" send requests to the server, which processes them and returns object ids to Perl which keeps them the reference te objects in the future.

BUGS AND DEFICIENCIES

When reporting a bug, please do the following:

 - Put "use Inline REPORTBUG;" at the top of your code, or 
   use the command line option "perl -MInline=REPORTBUG ...".
 - Run your code.
 - Follow the printed instructions.

Here are some things to watch out for:

You can't use the "package" Java directive when using Inline::Java.
You can't create public classes when using Inline::Java. This is due to the fact that Java requires that public classes be defined in a .java file of the same name (Inline::Java can't work this way).
You shouldn't name any of your classes starting "InlineJavaServer" or "InlineJavaPerl". Those are reserved for Inline::Java's own Java classes. Also do not name your classes 'B', 'S', 'I', 'J', 'F', 'D', 'C', 'Z' or 'L'. These classes seem to be used internally by Java to represent the primitive types.
If you upgrade Inline::Java from a previous version, be sure to delete your Inline directory so that Inline::Java's own Java classes get rebuilt to match the Perl code.

AUTHOR

Patrick LeBoutillier <patl@cpan.org>

Brian Ingerson <INGY@cpan.org> is the author of Inline.

COPYRIGHT

(see http://www.perl.com/perl/misc/Artistic.html)

1 POD Error

The following errors were encountered while parsing the POD:

Around line 965:: =back doesn't take any parameters, but you said =back Z<>

To install Inline::Java, copy and paste the appropriate command in to your terminal.

cpanm

cpanm Inline::Java

CPAN shell

perl -MCPAN -e shell
install Inline::Java

For more information on module installation, please visit the detailed CPAN module installation guide.

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