Root/Documentation/java.txt

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

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