[mirror_ubuntu-bionic-kernel.git] / Documentation / admin-guide / java.rst

Java(tm) Binary Kernel Support for Linux v1.03
----------------------------------------------

Linux beats them ALL! While all other OS's are TALKING about direct
support of Java Binaries in the OS, Linux is doing it!

You can execute Java applications and Java Applets just like any
other program after you have done the following:

1) You MUST FIRST install the Java Developers Kit for Linux.
   The Java on Linux HOWTO gives the details on getting and
   installing this. This HOWTO can be found at:

	ftp://sunsite.unc.edu/pub/Linux/docs/HOWTO/Java-HOWTO

   You should also set up a reasonable CLASSPATH environment
   variable to use Java applications that make use of any
   nonstandard classes (not included in the same directory
   as the application itself).

2) You have to compile BINFMT_MISC either as a module or into
   the kernel (``CONFIG_BINFMT_MISC``) and set it up properly.
   If you choose to compile it as a module, you will have
   to insert it manually with modprobe/insmod, as kmod
   cannot easily be supported with binfmt_misc.
   Read the file 'binfmt_misc.txt' in this directory to know
   more about the configuration process.

3) Add the following configuration items to binfmt_misc
   (you should really have read ``binfmt_misc.txt`` now):
   support for Java applications::

     ':Java:M::\xca\xfe\xba\xbe::/usr/local/bin/javawrapper:'

   support for executable Jar files::

     ':ExecutableJAR:E::jar::/usr/local/bin/jarwrapper:'

   support for Java Applets::

     ':Applet:E::html::/usr/bin/appletviewer:'

   or the following, if you want to be more selective::

     ':Applet:M::<!--applet::/usr/bin/appletviewer:'

   Of course you have to fix the path names. The path/file names given in this
   document match the Debian 2.1 system. (i.e. jdk installed in ``/usr``,
   custom wrappers from this document in ``/usr/local``)

   Note, that for the more selective applet support you have to modify
   existing html-files to contain ``<!--applet-->`` in the first line
   (``<`` has to be the first character!) to let this work!

   For the compiled Java programs you need a wrapper script like the
   following (this is because Java is broken in case of the filename
   handling), again fix the path names, both in the script and in the
   above given configuration string.

   You, too, need the little program after the script. Compile like::

	gcc -O2 -o javaclassname javaclassname.c

   and stick it to ``/usr/local/bin``.

   Both the javawrapper shellscript and the javaclassname program
   were supplied by Colin J. Watson <cjw44@cam.ac.uk>.

Javawrapper shell script::

  #!/bin/bash
  # /usr/local/bin/javawrapper - the wrapper for binfmt_misc/java

  if [ -z "$1" ]; then
	exec 1>&2
	echo Usage: $0 class-file
	exit 1
  fi

  CLASS=$1
  FQCLASS=`/usr/local/bin/javaclassname $1`
  FQCLASSN=`echo $FQCLASS | sed -e 's/^.*\.\([^.]*\)$/\1/'`
  FQCLASSP=`echo $FQCLASS | sed -e 's-\.-/-g' -e 's-^[^/]*$--' -e 's-/[^/]*$--'`

  # for example:
  # CLASS=Test.class
  # FQCLASS=foo.bar.Test
  # FQCLASSN=Test
  # FQCLASSP=foo/bar

  unset CLASSBASE

  declare -i LINKLEVEL=0

  while :; do
	if [ "`basename $CLASS .class`" == "$FQCLASSN" ]; then
		# See if this directory works straight off
		cd -L `dirname $CLASS`
		CLASSDIR=$PWD
		cd $OLDPWD
		if echo $CLASSDIR | grep -q "$FQCLASSP$"; then
			CLASSBASE=`echo $CLASSDIR | sed -e "s.$FQCLASSP$.."`
			break;
		fi
		# Try dereferencing the directory name
		cd -P `dirname $CLASS`
		CLASSDIR=$PWD
		cd $OLDPWD
		if echo $CLASSDIR | grep -q "$FQCLASSP$"; then
			CLASSBASE=`echo $CLASSDIR | sed -e "s.$FQCLASSP$.."`
			break;
		fi
		# If no other possible filename exists
		if [ ! -L $CLASS ]; then
			exec 1>&2
			echo $0:
			echo "  $CLASS should be in a" \
			     "directory tree called $FQCLASSP"
			exit 1
		fi
	fi
	if [ ! -L $CLASS ]; then break; fi
	# Go down one more level of symbolic links
	let LINKLEVEL+=1
	if [ $LINKLEVEL -gt 5 ]; then
		exec 1>&2
		echo $0:
		echo "  Too many symbolic links encountered"
		exit 1
	fi
	CLASS=`ls --color=no -l $CLASS | sed -e 's/^.* \([^ ]*\)$/\1/'`
  done

  if [ -z "$CLASSBASE" ]; then
	if [ -z "$FQCLASSP" ]; then
		GOODNAME=$FQCLASSN.class
	else
		GOODNAME=$FQCLASSP/$FQCLASSN.class
	fi
	exec 1>&2
	echo $0:
	echo "  $FQCLASS should be in a file called $GOODNAME"
	exit 1
  fi

  if ! echo $CLASSPATH | grep -q "^\(.*:\)*$CLASSBASE\(:.*\)*"; then
	# class is not in CLASSPATH, so prepend dir of class to CLASSPATH
	if [ -z "${CLASSPATH}" ] ; then
		export CLASSPATH=$CLASSBASE
	else
		export CLASSPATH=$CLASSBASE:$CLASSPATH
	fi
  fi

  shift
  /usr/bin/java $FQCLASS "$@"

javaclassname.c::

  /* javaclassname.c
 *
 * Extracts the class name from a Java class file; intended for use in a Java
 * wrapper of the type supported by the binfmt_misc option in the Linux kernel.
 *
 * Copyright (C) 1999 Colin J. Watson <cjw44@cam.ac.uk>.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

  #include <stdlib.h>
  #include <stdio.h>
  #include <stdarg.h>
  #include <sys/types.h>

  /* From Sun's Java VM Specification, as tag entries in the constant pool. */

  #define CP_UTF8 1
  #define CP_INTEGER 3
  #define CP_FLOAT 4
  #define CP_LONG 5
  #define CP_DOUBLE 6
  #define CP_CLASS 7
  #define CP_STRING 8
  #define CP_FIELDREF 9
  #define CP_METHODREF 10
  #define CP_INTERFACEMETHODREF 11
  #define CP_NAMEANDTYPE 12
  #define CP_METHODHANDLE 15
  #define CP_METHODTYPE 16
  #define CP_INVOKEDYNAMIC 18

  /* Define some commonly used error messages */

  #define seek_error() error("%s: Cannot seek\n", program)
  #define corrupt_error() error("%s: Class file corrupt\n", program)
  #define eof_error() error("%s: Unexpected end of file\n", program)
  #define utf8_error() error("%s: Only ASCII 1-255 supported\n", program);

  char *program;

  long *pool;

  u_int8_t read_8(FILE *classfile);
  u_int16_t read_16(FILE *classfile);
  void skip_constant(FILE *classfile, u_int16_t *cur);
  void error(const char *format, ...);
  int main(int argc, char **argv);

  /* Reads in an unsigned 8-bit integer. */
  u_int8_t read_8(FILE *classfile)
  {
	int b = fgetc(classfile);
	if(b == EOF)
		eof_error();
	return (u_int8_t)b;
  }

  /* Reads in an unsigned 16-bit integer. */
  u_int16_t read_16(FILE *classfile)
  {
	int b1, b2;
	b1 = fgetc(classfile);
	if(b1 == EOF)
		eof_error();
	b2 = fgetc(classfile);
	if(b2 == EOF)
		eof_error();
	return (u_int16_t)((b1 << 8) | b2);
  }

  /* Reads in a value from the constant pool. */
  void skip_constant(FILE *classfile, u_int16_t *cur)
  {
	u_int16_t len;
	int seekerr = 1;
	pool[*cur] = ftell(classfile);
	switch(read_8(classfile))
	{
	case CP_UTF8:
		len = read_16(classfile);
		seekerr = fseek(classfile, len, SEEK_CUR);
		break;
	case CP_CLASS:
	case CP_STRING:
	case CP_METHODTYPE:
		seekerr = fseek(classfile, 2, SEEK_CUR);
		break;
	case CP_METHODHANDLE:
		seekerr = fseek(classfile, 3, SEEK_CUR);
		break;
	case CP_INTEGER:
	case CP_FLOAT:
	case CP_FIELDREF:
	case CP_METHODREF:
	case CP_INTERFACEMETHODREF:
	case CP_NAMEANDTYPE:
	case CP_INVOKEDYNAMIC:
		seekerr = fseek(classfile, 4, SEEK_CUR);
		break;
	case CP_LONG:
	case CP_DOUBLE:
		seekerr = fseek(classfile, 8, SEEK_CUR);
		++(*cur);
		break;
	default:
		corrupt_error();
	}
	if(seekerr)
		seek_error();
  }

  void error(const char *format, ...)
  {
	va_list ap;
	va_start(ap, format);
	vfprintf(stderr, format, ap);
	va_end(ap);
	exit(1);
  }

  int main(int argc, char **argv)
  {
	FILE *classfile;
	u_int16_t cp_count, i, this_class, classinfo_ptr;
	u_int8_t length;

	program = argv[0];

	if(!argv[1])
		error("%s: Missing input file\n", program);
	classfile = fopen(argv[1], "rb");
	if(!classfile)
		error("%s: Error opening %s\n", program, argv[1]);

	if(fseek(classfile, 8, SEEK_SET))  /* skip magic and version numbers */
		seek_error();
	cp_count = read_16(classfile);
	pool = calloc(cp_count, sizeof(long));
	if(!pool)
		error("%s: Out of memory for constant pool\n", program);

	for(i = 1; i < cp_count; ++i)
		skip_constant(classfile, &i);
	if(fseek(classfile, 2, SEEK_CUR))	/* skip access flags */
		seek_error();

	this_class = read_16(classfile);
	if(this_class < 1 || this_class >= cp_count)
		corrupt_error();
	if(!pool[this_class] || pool[this_class] == -1)
		corrupt_error();
	if(fseek(classfile, pool[this_class] + 1, SEEK_SET))
		seek_error();

	classinfo_ptr = read_16(classfile);
	if(classinfo_ptr < 1 || classinfo_ptr >= cp_count)
		corrupt_error();
	if(!pool[classinfo_ptr] || pool[classinfo_ptr] == -1)
		corrupt_error();
	if(fseek(classfile, pool[classinfo_ptr] + 1, SEEK_SET))
		seek_error();

	length = read_16(classfile);
	for(i = 0; i < length; ++i)
	{
		u_int8_t x = read_8(classfile);
		if((x & 0x80) || !x)
		{
			if((x & 0xE0) == 0xC0)
			{
				u_int8_t y = read_8(classfile);
				if((y & 0xC0) == 0x80)
				{
					int c = ((x & 0x1f) << 6) + (y & 0x3f);
					if(c) putchar(c);
					else utf8_error();
				}
				else utf8_error();
			}
			else utf8_error();
		}
		else if(x == '/') putchar('.');
		else putchar(x);
	}
	putchar('\n');
	free(pool);
	fclose(classfile);
	return 0;
  }

jarwrapper::

  #!/bin/bash
  # /usr/local/java/bin/jarwrapper - the wrapper for binfmt_misc/jar

  java -jar $1


Now simply ``chmod +x`` the ``.class``, ``.jar`` and/or ``.html`` files you
want to execute.

To add a Java program to your path best put a symbolic link to the main
.class file into /usr/bin (or another place you like) omitting the .class
extension. The directory containing the original .class file will be
added to your CLASSPATH during execution.


To test your new setup, enter in the following simple Java app, and name
it "HelloWorld.java"::

	class HelloWorld {
		public static void main(String args[]) {
			System.out.println("Hello World!");
		}
	}

Now compile the application with::

	javac HelloWorld.java

Set the executable permissions of the binary file, with::

	chmod 755 HelloWorld.class

And then execute it::

	./HelloWorld.class


To execute Java Jar files, simple chmod the ``*.jar`` files to include
the execution bit, then just do::

       ./Application.jar


To execute Java Applets, simple chmod the ``*.html`` files to include
the execution bit, then just do::

	./Applet.html


originally by Brian A. Lantz, brian@lantz.com
heavily edited for binfmt_misc by Richard Günther
new scripts by Colin J. Watson <cjw44@cam.ac.uk>
added executable Jar file support by Kurt Huwig <kurt@iku-netz.de>
Commit	Line	Data
503c5bf9 MCC	1	Java(tm) Binary Kernel Support for Linux v1.03
503c5bf9 MCC	2	----------------------------------------------
1da177e4 LT	3
	4	Linux beats them ALL! While all other OS's are TALKING about direct
	5	support of Java Binaries in the OS, Linux is doing it!
	6
	7	You can execute Java applications and Java Applets just like any
	8	other program after you have done the following:
	9
	10	1) You MUST FIRST install the Java Developers Kit for Linux.
	11	The Java on Linux HOWTO gives the details on getting and
	12	installing this. This HOWTO can be found at:
	13
	14	ftp://sunsite.unc.edu/pub/Linux/docs/HOWTO/Java-HOWTO
	15
	16	You should also set up a reasonable CLASSPATH environment
	17	variable to use Java applications that make use of any
	18	nonstandard classes (not included in the same directory
	19	as the application itself).
	20
	21	2) You have to compile BINFMT_MISC either as a module or into
503c5bf9	22	the kernel (``CONFIG_BINFMT_MISC``) and set it up properly.
1da177e4 LT	23	If you choose to compile it as a module, you will have
1da177e4 LT	24	to insert it manually with modprobe/insmod, as kmod
503c5bf9	25	cannot easily be supported with binfmt_misc.
1da177e4 LT	26	Read the file 'binfmt_misc.txt' in this directory to know
	27	more about the configuration process.
	28
	29	3) Add the following configuration items to binfmt_misc
503c5bf9 MCC	30	(you should really have read ``binfmt_misc.txt`` now):
	31	support for Java applications::
	32
1da177e4	33	':Java:M::\xca\xfe\xba\xbe::/usr/local/bin/javawrapper:'
503c5bf9 MCC	34
	35	support for executable Jar files::
	36
1da177e4	37	':ExecutableJAR:E::jar::/usr/local/bin/jarwrapper:'
503c5bf9 MCC	38
	39	support for Java Applets::
	40
1da177e4	41	':Applet:E::html::/usr/bin/appletviewer:'
503c5bf9 MCC	42
	43	or the following, if you want to be more selective::
	44
1da177e4 LT	45	':Applet:M::<!--applet::/usr/bin/appletviewer:'
1da177e4 LT	46
59dd24d3	47	Of course you have to fix the path names. The path/file names given in this
503c5bf9 MCC	48	document match the Debian 2.1 system. (i.e. jdk installed in ``/usr``,
503c5bf9 MCC	49	custom wrappers from this document in ``/usr/local``)
1da177e4 LT	50
1da177e4 LT	51	Note, that for the more selective applet support you have to modify
503c5bf9 MCC	52	existing html-files to contain ``<!--applet-->`` in the first line
503c5bf9 MCC	53	(``<`` has to be the first character!) to let this work!
1da177e4 LT	54
	55	For the compiled Java programs you need a wrapper script like the
	56	following (this is because Java is broken in case of the filename
	57	handling), again fix the path names, both in the script and in the
	58	above given configuration string.
	59
503c5bf9 MCC	60	You, too, need the little program after the script. Compile like::
	61
	62	gcc -O2 -o javaclassname javaclassname.c
	63
	64	and stick it to ``/usr/local/bin``.
1da177e4 LT	65
	66	Both the javawrapper shellscript and the javaclassname program
	67	were supplied by Colin J. Watson <cjw44@cam.ac.uk>.
	68
503c5bf9 MCC	69	Javawrapper shell script::
	70
	71	#!/bin/bash
	72	# /usr/local/bin/javawrapper - the wrapper for binfmt_misc/java
1da177e4	73
503c5bf9	74	if [ -z "$1" ]; then
1da177e4 LT	75	exec 1>&2
	76	echo Usage: $0 class-file
	77	exit 1
503c5bf9	78	fi
1da177e4	79
503c5bf9 MCC	80	CLASS=$1
	81	FQCLASS=`/usr/local/bin/javaclassname $1`
	82	FQCLASSN=`echo $FQCLASS \| sed -e 's/^.\.\([^.]\)$/\1/'`
	83	FQCLASSP=`echo $FQCLASS \| sed -e 's-\.-/-g' -e 's-^[^/]$--' -e 's-/[^/]$--'`
1da177e4	84
503c5bf9 MCC	85	# for example:
	86	# CLASS=Test.class
	87	# FQCLASS=foo.bar.Test
	88	# FQCLASSN=Test
	89	# FQCLASSP=foo/bar
1da177e4	90
503c5bf9	91	unset CLASSBASE
1da177e4	92
503c5bf9	93	declare -i LINKLEVEL=0
1da177e4	94
503c5bf9	95	while :; do
1da177e4 LT	96	if [ "`basename $CLASS .class`" == "$FQCLASSN" ]; then
	97	# See if this directory works straight off
	98	cd -L `dirname $CLASS`
	99	CLASSDIR=$PWD
	100	cd $OLDPWD
	101	if echo $CLASSDIR \| grep -q "$FQCLASSP$"; then
	102	CLASSBASE=`echo $CLASSDIR \| sed -e "s.$FQCLASSP$.."`
	103	break;
	104	fi
	105	# Try dereferencing the directory name
	106	cd -P `dirname $CLASS`
	107	CLASSDIR=$PWD
	108	cd $OLDPWD
	109	if echo $CLASSDIR \| grep -q "$FQCLASSP$"; then
	110	CLASSBASE=`echo $CLASSDIR \| sed -e "s.$FQCLASSP$.."`
	111	break;
	112	fi
	113	# If no other possible filename exists
	114	if [ ! -L $CLASS ]; then
	115	exec 1>&2
	116	echo $0:
	117	echo " $CLASS should be in a" \
	118	"directory tree called $FQCLASSP"
	119	exit 1
	120	fi
	121	fi
	122	if [ ! -L $CLASS ]; then break; fi
	123	# Go down one more level of symbolic links
	124	let LINKLEVEL+=1
	125	if [ $LINKLEVEL -gt 5 ]; then
	126	exec 1>&2
	127	echo $0:
	128	echo " Too many symbolic links encountered"
	129	exit 1
	130	fi
	131	CLASS=`ls --color=no -l $CLASS \| sed -e 's/^.* \([^ ]*\)$/\1/'`
503c5bf9	132	done
1da177e4	133
503c5bf9	134	if [ -z "$CLASSBASE" ]; then
1da177e4 LT	135	if [ -z "$FQCLASSP" ]; then
	136	GOODNAME=$FQCLASSN.class
	137	else
	138	GOODNAME=$FQCLASSP/$FQCLASSN.class
	139	fi
	140	exec 1>&2
	141	echo $0:
	142	echo " $FQCLASS should be in a file called $GOODNAME"
	143	exit 1
503c5bf9	144	fi
1da177e4	145
503c5bf9	146	if ! echo $CLASSPATH \| grep -q "^\(.:\)$CLASSBASE\(:.\)"; then
1da177e4 LT	147	# class is not in CLASSPATH, so prepend dir of class to CLASSPATH
	148	if [ -z "${CLASSPATH}" ] ; then
	149	export CLASSPATH=$CLASSBASE
	150	else
	151	export CLASSPATH=$CLASSBASE:$CLASSPATH
	152	fi
503c5bf9	153	fi
1da177e4	154
503c5bf9 MCC	155	shift
503c5bf9 MCC	156	/usr/bin/java $FQCLASS "$@"
1da177e4	157
503c5bf9	158	javaclassname.c::
1da177e4	159
503c5bf9	160	/* javaclassname.c
1da177e4 LT	161	*
	162	* Extracts the class name from a Java class file; intended for use in a Java
	163	* wrapper of the type supported by the binfmt_misc option in the Linux kernel.
	164	*
	165	* Copyright (C) 1999 Colin J. Watson <cjw44@cam.ac.uk>.
	166	*
	167	* This program is free software; you can redistribute it and/or modify
	168	* it under the terms of the GNU General Public License as published by
	169	* the Free Software Foundation; either version 2 of the License, or
	170	* (at your option) any later version.
	171	*
	172	* This program is distributed in the hope that it will be useful,
	173	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	174	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	175	* GNU General Public License for more details.
	176	*
	177	* You should have received a copy of the GNU General Public License
	178	* along with this program; if not, write to the Free Software
	179	* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
	180	*/
	181
503c5bf9 MCC	182	#include <stdlib.h>
	183	#include <stdio.h>
	184	#include <stdarg.h>
	185	#include <sys/types.h>
	186
	187	/* From Sun's Java VM Specification, as tag entries in the constant pool. */
	188
	189	#define CP_UTF8 1
	190	#define CP_INTEGER 3
	191	#define CP_FLOAT 4
	192	#define CP_LONG 5
	193	#define CP_DOUBLE 6
	194	#define CP_CLASS 7
	195	#define CP_STRING 8
	196	#define CP_FIELDREF 9
	197	#define CP_METHODREF 10
	198	#define CP_INTERFACEMETHODREF 11
	199	#define CP_NAMEANDTYPE 12
	200	#define CP_METHODHANDLE 15
	201	#define CP_METHODTYPE 16
	202	#define CP_INVOKEDYNAMIC 18
	203
	204	/* Define some commonly used error messages */
	205
	206	#define seek_error() error("%s: Cannot seek\n", program)
	207	#define corrupt_error() error("%s: Class file corrupt\n", program)
	208	#define eof_error() error("%s: Unexpected end of file\n", program)
	209	#define utf8_error() error("%s: Only ASCII 1-255 supported\n", program);
	210
	211	char *program;
	212
	213	long *pool;
	214
	215	u_int8_t read_8(FILE *classfile);
	216	u_int16_t read_16(FILE *classfile);
	217	void skip_constant(FILE classfile, u_int16_t cur);
	218	void error(const char *format, ...);
	219	int main(int argc, char **argv);
	220
	221	/* Reads in an unsigned 8-bit integer. */
	222	u_int8_t read_8(FILE *classfile)
	223	{
1da177e4 LT	224	int b = fgetc(classfile);
	225	if(b == EOF)
	226	eof_error();
	227	return (u_int8_t)b;
503c5bf9	228	}
1da177e4	229
503c5bf9 MCC	230	/* Reads in an unsigned 16-bit integer. */
	231	u_int16_t read_16(FILE *classfile)
	232	{
1da177e4 LT	233	int b1, b2;
	234	b1 = fgetc(classfile);
	235	if(b1 == EOF)
	236	eof_error();
	237	b2 = fgetc(classfile);
	238	if(b2 == EOF)
	239	eof_error();
	240	return (u_int16_t)((b1 << 8) \| b2);
503c5bf9	241	}
1da177e4	242
503c5bf9 MCC	243	/* Reads in a value from the constant pool. */
	244	void skip_constant(FILE classfile, u_int16_t cur)
	245	{
1da177e4 LT	246	u_int16_t len;
	247	int seekerr = 1;
	248	pool[*cur] = ftell(classfile);
	249	switch(read_8(classfile))
	250	{
	251	case CP_UTF8:
	252	len = read_16(classfile);
	253	seekerr = fseek(classfile, len, SEEK_CUR);
	254	break;
	255	case CP_CLASS:
	256	case CP_STRING:
f76f133b	257	case CP_METHODTYPE:
1da177e4 LT	258	seekerr = fseek(classfile, 2, SEEK_CUR);
1da177e4 LT	259	break;
f76f133b JC	260	case CP_METHODHANDLE:
	261	seekerr = fseek(classfile, 3, SEEK_CUR);
	262	break;
1da177e4 LT	263	case CP_INTEGER:
	264	case CP_FLOAT:
	265	case CP_FIELDREF:
	266	case CP_METHODREF:
	267	case CP_INTERFACEMETHODREF:
	268	case CP_NAMEANDTYPE:
f76f133b	269	case CP_INVOKEDYNAMIC:
1da177e4 LT	270	seekerr = fseek(classfile, 4, SEEK_CUR);
	271	break;
	272	case CP_LONG:
	273	case CP_DOUBLE:
	274	seekerr = fseek(classfile, 8, SEEK_CUR);
	275	++(*cur);
	276	break;
	277	default:
	278	corrupt_error();
	279	}
	280	if(seekerr)
	281	seek_error();
503c5bf9	282	}
1da177e4	283
503c5bf9 MCC	284	void error(const char *format, ...)
503c5bf9 MCC	285	{
1da177e4 LT	286	va_list ap;
	287	va_start(ap, format);
	288	vfprintf(stderr, format, ap);
	289	va_end(ap);
	290	exit(1);
503c5bf9	291	}
1da177e4	292
503c5bf9 MCC	293	int main(int argc, char **argv)
503c5bf9 MCC	294	{
1da177e4 LT	295	FILE *classfile;
	296	u_int16_t cp_count, i, this_class, classinfo_ptr;
	297	u_int8_t length;
	298
	299	program = argv[0];
	300
	301	if(!argv[1])
	302	error("%s: Missing input file\n", program);
	303	classfile = fopen(argv[1], "rb");
	304	if(!classfile)
	305	error("%s: Error opening %s\n", program, argv[1]);
	306
	307	if(fseek(classfile, 8, SEEK_SET)) /* skip magic and version numbers */
	308	seek_error();
	309	cp_count = read_16(classfile);
	310	pool = calloc(cp_count, sizeof(long));
	311	if(!pool)
	312	error("%s: Out of memory for constant pool\n", program);
	313
	314	for(i = 1; i < cp_count; ++i)
	315	skip_constant(classfile, &i);
	316	if(fseek(classfile, 2, SEEK_CUR)) /* skip access flags */
	317	seek_error();
	318
	319	this_class = read_16(classfile);
	320	if(this_class < 1 \|\| this_class >= cp_count)
	321	corrupt_error();
	322	if(!pool[this_class] \|\| pool[this_class] == -1)
	323	corrupt_error();
	324	if(fseek(classfile, pool[this_class] + 1, SEEK_SET))
	325	seek_error();
	326
	327	classinfo_ptr = read_16(classfile);
	328	if(classinfo_ptr < 1 \|\| classinfo_ptr >= cp_count)
	329	corrupt_error();
	330	if(!pool[classinfo_ptr] \|\| pool[classinfo_ptr] == -1)
	331	corrupt_error();
	332	if(fseek(classfile, pool[classinfo_ptr] + 1, SEEK_SET))
	333	seek_error();
	334
	335	length = read_16(classfile);
	336	for(i = 0; i < length; ++i)
	337	{
	338	u_int8_t x = read_8(classfile);
	339	if((x & 0x80) \|\| !x)
	340	{
	341	if((x & 0xE0) == 0xC0)
	342	{
	343	u_int8_t y = read_8(classfile);
	344	if((y & 0xC0) == 0x80)
	345	{
	346	int c = ((x & 0x1f) << 6) + (y & 0x3f);
	347	if(c) putchar(c);
	348	else utf8_error();
	349	}
	350	else utf8_error();
	351	}
	352	else utf8_error();
	353	}
	354	else if(x == '/') putchar('.');
	355	else putchar(x);
	356	}
	357	putchar('\n');
	358	free(pool);
359	fclose(classfile);
360	return 0;
503c5bf9	361	}
1da177e4	362
503c5bf9	363	jarwrapper::
1da177e4	364
503c5bf9 MCC	365	#!/bin/bash
503c5bf9 MCC	366	# /usr/local/java/bin/jarwrapper - the wrapper for binfmt_misc/jar
1da177e4	367
503c5bf9	368	java -jar $1
1da177e4 LT	369
1da177e4 LT	370
503c5bf9 MCC	371	Now simply ``chmod +x`` the ``.class``, ``.jar`` and/or ``.html`` files you
	372	want to execute.
	373
1da177e4 LT	374	To add a Java program to your path best put a symbolic link to the main
	375	.class file into /usr/bin (or another place you like) omitting the .class
	376	extension. The directory containing the original .class file will be
	377	added to your CLASSPATH during execution.
	378
	379
	380	To test your new setup, enter in the following simple Java app, and name
503c5bf9	381	it "HelloWorld.java"::
1da177e4 LT	382
	383	class HelloWorld {
	384	public static void main(String args[]) {
	385	System.out.println("Hello World!");
	386	}
	387	}
	388
503c5bf9 MCC	389	Now compile the application with::
503c5bf9 MCC	390
1da177e4 LT	391	javac HelloWorld.java
1da177e4 LT	392
503c5bf9 MCC	393	Set the executable permissions of the binary file, with::
503c5bf9 MCC	394
1da177e4 LT	395	chmod 755 HelloWorld.class
1da177e4 LT	396
503c5bf9 MCC	397	And then execute it::
503c5bf9 MCC	398
1da177e4 LT	399	./HelloWorld.class
	400
	401
503c5bf9 MCC	402	To execute Java Jar files, simple chmod the ``*.jar`` files to include
	403	the execution bit, then just do::
	404
1da177e4 LT	405	./Application.jar
	406
	407
503c5bf9 MCC	408	To execute Java Applets, simple chmod the ``*.html`` files to include
	409	the execution bit, then just do::
	410
1da177e4 LT	411	./Applet.html
	412
	413
	414	originally by Brian A. Lantz, brian@lantz.com
be2a608b	415	heavily edited for binfmt_misc by Richard Günther
1da177e4 LT	416	new scripts by Colin J. Watson <cjw44@cam.ac.uk>
1da177e4 LT	417	added executable Jar file support by Kurt Huwig <kurt@iku-netz.de>