| Inline::Java(3pm) | User Contributed Perl Documentation | Inline::Java(3pm) |
Inline::Java - Write Perl classes in Java.
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
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.
As of version 0.62, the minimum JDK supported is JDK 7. This is due to the "diamond operator" "<>" used for generic "ArrayList"s among others.
"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 (the subroutine should return source code), or an array reference (the 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 a Java 2 SDK on your machine. This is done using one of the following techniques:
If none of these are specified, "Inline::Java" will use the Java 2 SDK that was specified at install time (see below).
When "Inline::Java" was installed, the path to the Java 2 SDK that was used was stored in a file called default_j2sdk.pl that resides within the "Inline::Java" module. You can obtain this path by using the following command:
% perl -MInline::Java=j2sdk
If you wish to permanently change the default Java 2 SDK that is used by "Inline::Java", edit this file and change the value found there. If you wish use a different Java 2 SDK temporarily, see the J2SDK configuration option described below.
Additionally, you can use the following command to get the list of directories that you should put in you shared library path when using the JNI extension:
% perl -MInline::Java=so_dirs
There are a number of configuration options that dictate the behavior of "Inline::Java":
Ex: j2sdk => '/my/java/2/sdk/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.
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.
Ex: host => 'jvm.server.com'
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.
Ex: bind => '192.168.1.1'
Ex: bind => '0.0.0.0'
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.
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.
Ex: classpath => '/my/other/java/classses'
Ex: jni => 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.
Ex: extra_java_args => '-Xmx96m'
Note: extra_java_args 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.
Ex: embedded_jni => 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. Also, the embedded_jni option automatically sets the JNI option.
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.
Ex: start_jvm => 0
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.
Ex: private => 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.
1 = Major program steps
2 = Object creation/destruction
3 = Method/member accesses + packet dumps
4 = Everything else
5 = Data structure dumps
Ex: debug => 2
Ex: debugger => 1
Ex: warn_method_select => 1
Ex: study => ['java.lang.HashMap', 'my.class']
Ex: autostudy => 1
Ex: package => 'main'
Ex: native_doubles => 1
Every configuration option listed above, with the exception of STUDY, can be specified using an environment variable named using the following convention:
PERL_INLINE_JAVA_<option name>
For example, you can specify the JNI option using the PERL_INLINE_JAVA_JNI environment variable.
Note that environment variables take precedence over options specified in the script itself.
Under Win32, you can also use set the PERL_INLINE_JAVA_COMMAND_COM environment variable to a true value to indicate that you are using the command.com shell. However, "Inline::Java" should normally be able to determine this on its own.
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.
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
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<String, String> h = new HashMap<>() ;
h.put("key", "value") ;
return h ;
}
public String do_stuff_to_hash(HashMap<String, String> 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. See the STUDYING section for more information on how to tell "Inline::Java" to learn about these classes.
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_5::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...
You can also send, receive and modify 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
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 a custom exception you have in your code, you will have access to that exception object's public methods just like any other Java object in "Inline::Java". Note: "Inline::Java" uses eval under the hood, so it recommended that you store any exception in a temporary variable before processing it, especially f you will be calling other "Inline::Java" functions. 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.
Java filehandles (java.io.Reader, java.io.Writer, java.io.InputStream or java.io.OutputStream objects) can be wrapped the "Inline::Java::Handle" class to allow reading or writing from Perl. Here's an example:
use Inline Java => <<'END' ;
import java.io.* ;
class Pod_91 {
public static Reader getReader(String file) throws FileNotFoundException {
return new FileReader(file) ;
}
}
END
my $o = Pod_91->getReader('t/t13.txt') ;
my $h = Inline::Java::Handle->new($o) ;
# read one line
my $text = <$h>;
chomp $text;
print($text . "\n") ; # prints 1
What's important to understand is that the returned "Inline::Java::Handle" object actually contains a reference to the Java reader or writer. It is probably a good idea to undef it once you have completed the I/O operations so that the underlying Java object may be freed.
See Inline::Java::Callbacks for more information on making callbacks.
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'],
autostudy => 1,
) ;
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 your 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.
In some cases you may not know which classes to study until runtime. In these cases you can use the study_classes() function:
use Inline (
Java => 'study',
study => [],
) ;
use Inline::Java qw(study_classes) ;
study_classes(['java.util.HashMap'], undef) ;
my $hm = new java::util::HashMap() ;
$hm->put("key", "value") ;
my $val = $hm->get("key") ;
print($val . "\n") ; # prints value
The study_classes() function takes 2 arguments, a reference to an array of class names (like the STUDY configuration option) and the name of the package in which to bind those classes. If the name of the package is undefined, the classes will be bound to the current (caller) package.
Note: You can only specify the names of packages in which you have previously "used" "Inline::Java".
Sometimes you need to manipulate a Java object using a specific subtype. That's when type casting is necessary. Here's an example of this:
use Inline (
Java => 'study',
study => ['java.util.HashMap'],
autostudy => 1,
) ;
use Inline::Java qw(cast) ;
my $hm = new java::util::HashMap() ;
$hm->put('key', 'value') ;
my $entries = $hm->entrySet()->toArray() ;
foreach my $e (@{$entries}){
# print($e->getKey() . "\n") ; # No!
print(cast('java.util.Map$Entry', $e)->getKey() . "\n") ; # prints key
}
In this case, "Inline::Java" knows that $e is of type java.util.HashMap$Entry. The problem is that this type is not public, and therefore we can't access the object through that type. We must cast it to a java.util.Map$Entry, which is a public interface and will allow us to access the getKey() method.
You can also use type casting to force the selection of a specific method signature for methods that have multiple signatures. See examples similar to this in the "TYPE COERCING" section below.
Type coercing is the equivalent of casting for primitives types and arrays. It is used to force the selection if a specific method signature when "Inline::Java" has multiple choices. The coerce function returns a special object that can only be used when calling Java methods or assigning Java members. Here is an example:
use Inline Java => <<'END' ;
class Pod_101 {
public Pod_101(){
}
public String f(int i){
return "int" ;
}
public String f(char c){
return "char" ;
}
}
END
my $obj = new Pod_101() ;
print($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(coerce) ;
$obj->f(coerce('char', '5')) ;
# or
$obj->f(Inline::Java::coerce('char', '5')) ;
The coerce function forces the selection of the matching signature. Note that the coerce must match the argument type exactly. Coercing to a class that extends the argument type will not work.
Another case where type coercing is needed 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 three-parameter version of the coerce function to do this:
$obj->{o} = Inline::Java::coerce(
"java.lang.Object",
[1, 2, 3],
"[Ljava.lang.String;") ;
This tells "Inline::Java" to validate your Perl list as a String [], and then coerce 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 coerce:
$obj->{o} = $obj->{a} ;
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 explicitly by doing one of the following:
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.
Starting with version 0.30, the "Inline::Java" JVM can now be shared between multiple processes. The first process to start creates the JVM but does not shut it down on exit. All other processes can then 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.
Note: The Java System.out stream is closed in SHARED_JVM mode.
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,
directory => '/somewhere/your/web/server/can/write',
) ;
my $c = new Pod_counter() ;
my $q = new CGI() ;
print
$q->start_html() .
"This page has been accessed " . $c->{cnt} . " times." .
$q->end_html() ;
In this scenario, the first CGI to execute will start the JVM, but does not shut it down on exit. Subsequent CGI, since they have the shared_jvm option enabled, will try to connect to the 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.
See the BUGS AND DEFICIENCIES section if you have problems starting the shared_jvm server in a CGI.
Here is an example of how to use "Inline::Java" under mod_perl:
use Apache2::Const qw(:common) ;
use Inline (
Java => <<'END',
class Pod_counter {
public static int cnt = 0 ;
public Pod_counter(){
cnt++ ;
}
}
END
shared_jvm => 1,
directory => '/somewhere/your/web/server/can/write',
) ;
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 OK ;
}
See USING Inline::Java IN A CGI for more details.
If you are using ModPerl::Registry, make sure to use the "PACKAGE" configuration option to specify the package in which "Inline::Java" should bind the Java code, since ModPerl::Registry will place your code in a package with a unpredictable name.
See the BUGS AND DEFICIENCIES section if you have problems starting the shared_jvm server under MOD_PERL.
If you are loading "Inline::Java" during your server startup (common practice to increase shared memory and reduce run time) and you are using "shared_jvm", then your Apache processes will all share the same socktd connection to that JVM. This will result in garbled communication and strange errors (like "Can't receive packet from JVM", "Broken pipe", etc).
To fix this you need to tell Apache that after each child process has forked they each need to create their own connections to the JVM. This is done during the "ChildInit" stage.
For Apache 1.3.x this could look like:
# in httpd.conf PerlChildInitHandler MyProject::JavaReconnect
And "MyProject::JavaReconnect" could be as simple as this:
package MyProject::JavaReconnect;
sub handler($$) { Inline::Java::reconnect_JVM() }
1;
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:
% perl -MInline::Java::Server=status
% perl -MInline::Java::Server=start
% perl -MInline::Java::Server=stop
% perl -MInline::Java::Server=restart
You can specify "Inline::Java" options by setting the proper environment variables, and you can also set the _Inline directory by using the PERL_INLINE_JAVA_DIRECTORY environment variable.
In addition, you may also wish to set the start_jvm option to 0 in your scripts to prevent them from trying to start their own JVM if they can't find one, thereby causing problems.
Inline::Java::Callback, Inline::Java::PerlNatives, Inline::Java::PerlInterpreter.
For information about using "Inline", see Inline.
For information about other Inline languages, see Inline-Support.
"Inline::Java"'s mailing list is <inline@perl.org>. To subscribe, send an email to <inline-subscribe@perl.org>
Patrick LeBoutillier <patl@cpan.org> is the author of Inline::Java.
Brian Ingerson <ingy@cpan.org> is the author of Inline.
Copyright (c) 2001-2005, Patrick LeBoutillier.
All Rights Reserved. This module is free software. It may be used, redistributed and/or modified under the terms of the Perl Artistic License. See http://www.perl.com/perl/misc/Artistic.html for more details.
| 2018-11-02 | perl v5.28.0 |