Difference between revisions of "pas2jni"

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Revision as of 15:00, 8 January 2015

Overview

The pas2jni utility generates a JNI (Java Native Interface) bridge for a Pascal code. Then the Pascal code (including classes and other advanced features) can be easily used in Java programs.

For example you can do the following in Java:

import pas.classes.*;

...

TStringList sl = TStringList.Create();
sl.Add("Hello.");
String s = sl.getStrings(0);
sl.Free();

...

The following Pascal features are supported by pas2jni:

  • function/procedure;
  • var/out parameters;
  • class;
  • record;
  • property;
  • constant;
  • enum;
  • set;
  • TGuid type;
  • pointer type;
  • string types;
  • all numeric types;
  • method poitner.

USUPPORTED features:

  • array (Can be added in future);
  • procedure pointer (Not possible to implement. To workaround this limitation create a procedure handler in your Pascal code and call a method pointer declared is some global Pascal class. The you can assign this method pointer from a Java code).

Shared libraries, generated by pas2jni were tested with Java on Windows and Android. It should work on other systems as well.

How to use

pas2jni uses the PPUDump utility included with Free Pascal Compiler to read unit interfaces. Therefore your Pascal code must be first compiled with FPC. When your units are compiled, you can run pas2jni. You need to specify a list of main units and units search path. When you specify a main unit, all its interface declarations will be available in Java. For linked units only used declarations will be available. You can fine tune included/excluded declaration using -I and -E command line options.

The basic invocation of pas2jni:

pas2jni myunit -U/path/to/my/units;/path/to/FPC/units/*

Here you specify myunit as the main unit and provide path to your compiled units and FPC compiled units.

After successfull run of pas2jni you will get the following output files:

  • file myunitjni.pas - a generated library unit to be compiled to a shared library. It will contain all your Pascal code to be used from Java.
  • folder pas - generated Java package pas to be used in your Java program. Interface to each Pascal unit is placed to a separate Java public class.

Note: You need to use ppudump of the same version as the FPC compiler. Use the -D switch to specify correct ppudump if it is not in PATH.

Custom handlers

It is possible to define the following custom handlers in your Pascal code.

procedure JNI_OnException;

  • It is called when an unhandled Pascal exception occurs. For example, you can log a stack back trace in this handler.

Custom handlers must be public and defined in one of the main units specified when calling pas2jni.

Coding tips

Setting handlers (method pointers) in a Java code.

For example there is the following event handler in your Pascal code:

TMyClass = class
...
  property OnChange: TNotifyEvent;
...
end;

In a Java code you get the following TMyClass instance:

TMyClass myclass = TMyClass.Create();

It is possible set a Java handler in 2 ways:

1) Place the handler in-line.

...
  myclass.setOnChange(
      new TNotifyEvent() {
        protected void Execute(TObject Sender) {
          // The handler code
        }
      }
    );
...

2) Define the handler as a method in a class.

public class MyJavaClass {
  private void DoOnChange(TObject Sender) {
    // The handler code
  }

  public void main() {
    ...
    // Set the handler to the method with the "DoOnChange" name in the current class (this).
    myclass.setOnChange( new TNotifyEvent(this, "DoOnChange") );
    ...
  }
}

Command line options

Usage: pas2jni [options] <unit> [<unit2> <unit3> ...]

Options:
  -U<path> - Unit search path, semicolon delimited. Wildcards are allowed.
  -L<name> - Set output library name.
  -P<name> - Set Java package name.
  -O<path> - Set output path for Pascal files.
  -J<path> - Set output path for Java files.
  -D<prog> - Set full path to the "ppudump" program.
  -I<list> - Include the list of specified objects in the output. The list is
             semicolon delimited. To read the list from a file use -I@<file>
  -E<list> - Exclude the list of specified objects from the output. The list is
             semicolon delimited. To read the list from a file use -E@<file>
  -?       - Show this help information.