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updated java guide per an email exchange with a user and nichoj

1 <?xml version="1.0" encoding="UTF-8"?>
2 <!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/java.xml,v 1.39 2007/04/29 02:36:16 nightmorph Exp $ -->
3 <!DOCTYPE guide SYSTEM "/dtd/guide.dtd">
4
5 <guide link="/doc/en/java.xml">
6 <title>Gentoo Java Guide</title>
7
8 <author title="Author">
9 <mail link="nichoj@gentoo.org">Joshua Nichols</mail>
10 </author>
11 <author title="Author">
12 <mail link="karltk@gentoo.org">Karl Trygve Kalleberg</mail>
13 </author>
14 <author title="Editor">
15 <mail link="nightmorph@gentoo.org">Joshua Saddler</mail>
16 </author>
17
18 <abstract>
19 This guide will introduce you to Java and explain how to use Java with Gentoo
20 Linux.
21 </abstract>
22
23 <!-- The content of this document is licensed under the CC-BY-SA license -->
24 <!-- See http://creativecommons.org/licenses/by-sa/2.5 -->
25 <license/>
26
27 <version>0.16</version>
28 <date>2008-01-01</date>
29
30 <chapter>
31 <title>What is Java?</title>
32 <section>
33 <title>Overview</title>
34 <body>
35
36 <p>
37 Java is a programming language developed by engineers of Sun Microsystems. The
38 language is object-oriented and designed to run on multiple platforms without
39 the need of recompiling code for each platform. Although Java can be compiled
40 as a native program, much of Java's popularity can be attributed to its
41 portability, along with other features such as garbage collection. To make
42 platform independence possible the Java compiler compiles the Java code to an
43 intermediate representation called "Java bytecode" that runs on a JRE (Java
44 Runtime Environment) and not directly on the operating system.
45 </p>
46
47 <p>
48 In order to run Java bytecode, one needs to have a JRE (Java Runtime
49 Environment) installed. A JRE provides core libraries, a platform dependent
50 Java Virtual Machine, plugins for browsers, among other things. A JDK (Java
51 Development Kit) adds programming tools, such as a bytecode compiler and a
52 debugger.
53 </p>
54
55 </body>
56 </section>
57 </chapter>
58
59 <chapter>
60 <title>Before You Begin</title>
61 <section>
62 <title>Existing installs</title>
63 <body>
64
65 <p>
66 For existing installs, regardless of if you have installed anything Java
67 before, make sure you have followed the <uri
68 link="/proj/en/java/java-upgrade.xml">Java Upgrade Guide</uri>.
69 </p>
70
71 </body>
72 </section>
73 <section>
74 <title>New installs</title>
75 <body>
76
77 <p>
78 New installs should require no further preparation.
79 </p>
80
81 </body>
82 </section>
83 </chapter>
84
85 <chapter>
86 <title>Installing a Virtual Machine</title>
87 <section>
88 <title>The choices</title>
89 <body>
90
91 <p>
92 Gentoo provides numerous Runtime Environments (JREs) and Development Kits
93 (JDKs). Among the current choices, we have:
94 </p>
95
96 <table>
97 <tr>
98 <th>Vendor</th>
99 <th>JDK</th>
100 <th>JRE</th>
101 </tr>
102 <tr>
103 <ti>The Blackdown Java Kit</ti>
104 <ti>dev-java/blackdown-jdk</ti>
105 <ti>dev-java/blackdown-jre</ti>
106 </tr>
107 <tr>
108 <ti>Sun's Java Kit</ti>
109 <ti>dev-java/sun-jdk</ti>
110 <ti>dev-java/sun-jre-bin</ti>
111 </tr>
112 <tr>
113 <ti>The IBM Java Kit</ti>
114 <ti>dev-java/ibm-jdk-bin</ti>
115 <ti>dev-java/ibm-jre-bin</ti>
116 </tr>
117 <tr>
118 <ti>BEA WebLogic's J2SE Development Kit</ti>
119 <ti>dev-java/jrockit-jdk-bin</ti>
120 </tr>
121 </table>
122
123 <!--
124 TODO: list free implementations?
125 note about not drop-in replacements
126 kaffe/sablevm/gcj/jamvm
127 -->
128 <p>
129 The default for Java 1.4 is the Blackdown JRE/JDK pair, as it is freely
130 ("free as in beer") available without any registration fuss.
131 </p>
132
133 <p>
134 JREs and JDKs from Sun, IBM, and BEA are generally faster, but getting them
135 is a bit more work, as you are required to read and accept their license before
136 downloading (IBM additionally requires you to register).
137 </p>
138
139 </body>
140 </section>
141 <section>
142 <title>Installing a JRE/JDKs</title>
143 <body>
144
145 <p>
146 To install your profile's default JDK, you can run <c>emerge virtual/jdk</c>.
147 Or to install your profile's default JRE, you can <c>emerge virtual/jre</c>.
148 </p>
149
150 <p>
151 In recent events, Sun has relicensed their JDK and JRE under a more Linux
152 distro friendly license. As a result, Sun releases Java 1.5 and onwards are
153 freely downloadable, without any further hassle.
154 </p>
155
156 <note>
157 A JDK also includes a JRE, so if you install a JDK you shouldn't have to also
158 have to install a JRE.
159 </note>
160
161 </body>
162 </section>
163 <section>
164 <title>Installing fetch-restricted virtual machines</title>
165 <body>
166
167 <p>
168 As already mentioned, some of the JDKs and JREs require you to jump through a
169 few hoops before installing. Simply emerge the packages as you normally would.
170 The ebuilds will then instruct you where to go and what to download.
171 </p>
172
173 <p>
174 You should download the indicated file(s) into
175 <path>/usr/portage/distfiles</path>. Once there, you can rerun the emerge
176 command, at which point the JRE/JDK will be begin to install.
177 </p>
178
179 </body>
180 </section>
181 </chapter>
182
183 <chapter>
184 <title>Configuring your virtual machine</title>
185 <section>
186 <title>Overview</title>
187 <body>
188
189 <p>
190 Gentoo has the ability to have multiple JDKs and JREs installed without causing
191 conflicts.
192 </p>
193
194 <p>
195 Using the <c>java-config</c> tool, you can set the system-wide default
196 (provided you have root access). Users can also use <c>java-config</c> to set
197 up their own personal default.
198 </p>
199
200 <note>
201 You can also use <e>eselect</e> to change the system and user vm. See
202 <c>eselect java-vm help</c>.
203 </note>
204
205 </body>
206 </section>
207 <section>
208 <title>Setting a default virtual machine</title>
209 <body>
210
211 <p>
212 Running the command <c>java-config --list-available-vms</c> will give you a
213 list of all JREs and JDKs installed on your system. Here is an example of
214 output:
215 </p>
216
217 <pre caption="Listing available VMs">
218 # <i>java-config --list-available-vms</i>
219 The following VMs are available for generation-2:
220 1) Blackdown JDK 1.4.2.03 [blackdown-jdk-1.4.2]
221 2) Blackdown JRE 1.4.2.03 [blackdown-jre-1.4.2]
222 3) Blackdown 32bit JRE 1.4.2.03 [emul-linux-x86-java-1.4.2]
223 4) Sun 32bit JRE 1.5.0.08 [emul-linux-x86-java-1.5]
224 5) Kaffe 1.1.7 [kaffe]
225 *) Sun JDK 1.5.0.08 [sun-jdk-1.5]
226 </pre>
227
228 <p>
229 The <e>*</e> indicates this is the current active vm (system-vm or user-vm when
230 set). The name in the brackets (<e>[]</e>) is the handle or ID for that
231 particular VM. You use the handle or the number to <c>java-config
232 --set-system-vm</c>. Here is an example of how to set the system VM.
233 </p>
234
235 <pre caption="Setting the System VM">
236 <comment>(By handle (preferred))</comment>
237 # <i>java-config --set-system-vm blackdown-jdk-1.4</i>
238 Now using blackdown-jdk-1.4 as your generation-2 system JVM
239 <comment>(By number)</comment>
240 # <i>java-config --set-system-vm 6</i>
241 Now using sun-jdk-1.5 as your generation-2 system JVM
242 </pre>
243
244 <p>
245 As a regular user, you can use <c>java-config --set-user-vm</c>.
246 </p>
247
248 <note>
249 You no longer have to <c>source</c> the profile for updates to the user/system
250 VM take place.
251 </note>
252
253 </body>
254 </section>
255 <section id="preferred-vm">
256 <title>Preferred VM</title>
257 <body>
258
259 <p>
260 While merging Java packages, the VM can and will be switched as necessary.
261 </p>
262
263 <p>
264 Because of the wide variety of available VMs, we do not have the resources to
265 test and verify every package works on all of them. So to ensure that every
266 packages merges smoothly, we have defined a list of <e>default/supported
267 VMs</e> per arch. You can find them in
268 <path>/usr/share/java-config-2/config/jdk-defaults.conf</path>. When you are
269 merging a Java package, and it detects one of the VM in that file is installed,
270 it will automatically use that VM, instead of the system-vm.
271 </p>
272
273 <p>
274 The merge time VM switching is also needed when, for example, your system-vm is
275 set a 1.4 VM and the package you are merging requires a 1.5 VM. While merging
276 it will use the preferred 1.5 VM, leaving your system-vm choice intact.
277 </p>
278
279 <p>
280 Of course, Gentoo is all about choice, so you can override these defaults in
281 <path>/etc/java-config-2/build/jdk.conf</path> and have complete control over
282 which VM will get used. Some examples:
283 </p>
284
285 <pre caption="Example /etc/java-config-2/build/jdk.conf">
286 <comment>(I always want it to use a sun-jdk, ie sun-jdk-1.4 for 1.4, sun-jdk-1.5 for 1.5, etc)</comment>
287 *=sun-jdk
288 </pre>
289
290 <pre caption="Example /etc/java-config-2/build/jdk.conf">
291 <comment>(Always use sun-jdk-1.5 wherever possible, except for when a 1.4 or 1.3 VM is explicitly required)</comment>
292 *=sun-jdk-1.5
293 </pre>
294
295 <pre caption="Example /etc/java-config-2/build/jdk.conf">
296 <comment># For 1.3 I prefer sun-jdk 1.4 but when it is not available, use ibm-jdk-bin,
297 # For 1.4, use blackdown-jdk, and for 1.5, use sun-jdk </comment>
298 1.3=sun-jdk-1.4 ibm-jdk-bin
299 1.4=blackdown-jdk
300 1.5=sun-jdk
301 </pre>
302
303 <warn>
304 You do not have to edit this file. If you change these options to use a
305 unsupported VM, things could possibly break. Bugs reported with a unsupported
306 VM won't be prioritized as much as bugs present within supported VMs.
307 </warn>
308
309 </body>
310 </section>
311 </chapter>
312
313 <chapter>
314 <title>Compilers</title>
315 <section>
316 <body>
317
318 <p>
319 The standard Java compiler used for building is javac, which comes with each
320 JDK. In addition to configuring the VM used at build time, it is also possible
321 configure which compiler is used. Essentially, you define a list your
322 preference for which compiler to use in
323 <path>/etc/java-config-2/build/compilers.conf</path>.
324 </p>
325
326 <pre caption="/etc/java-config-2/build/compilers.conf">
327 # If the ebuild supports it
328 # it will check the COMPILERS var front to back and
329 # use the first compiler that is installed
330
331 COMPILERS="ecj-3.1 jikes javac"
332 </pre>
333
334 <p>
335 Some compilers don't support all possible -target and -source arguments.
336 Therefore, each compiler in the list is checked to see if it can support the
337 desired -source/-target. javac will work in all cases, so if no other suitable
338 compiler is found, it will be used instead.
339 </p>
340
341 <p>
342 More details about each compiler are provided below:
343 </p>
344
345 <table>
346 <tr>
347 <th>Name</th>
348 <th>Handle</th>
349 <th>Package</th>
350 <th>Description</th>
351 </tr>
352 <tr>
353 <ti>javac</ti>
354 <ti>javac</ti>
355 <ti>N/A</ti>
356 <ti>
357 This is the default compiler that will be used, and comes with each JDK.
358 </ti>
359 </tr>
360 <tr>
361 <ti>jikes</ti>
362 <ti>jikes</ti>
363 <ti>dev-java/jikes</ti>
364 <ti>
365 Jikes was originally developed by IBM. Anecdotally, it is generally quicker
366 than javac. Note however, that it is more pedantic, and will fail under a
367 few circumstances where javac has no issue. It also does not support Java
368 1.5 syntax yet.
369 </ti>
370 </tr>
371 <tr>
372 <ti>Eclipse Compiler for Java</ti>
373 <ti>ecj-3.1</ti>
374 <ti>=dev-java/eclipse-ecj-3.1*</ti>
375 <ti>
376 ECJ is the compiler used by the Eclipse software development kit. It is
377 very full featured, and is pretty fast. It does support Java 1.5 syntax.
378 </ti>
379 </tr>
380 </table>
381
382 </body>
383 </section>
384 </chapter>
385
386 <chapter>
387 <title>Setting a default CLASSPATH</title>
388 <section>
389 <body>
390
391 <warn>
392 The options explained in this section should be considered deprecated and will
393 most likely be removed in the future. We strongly recommend against using
394 these, because your Java projects or application should ideally manage their
395 own classpaths. If you choose to specify a default CLASSPATH, some applications
396 may behave unexpectedly, because classes they weren't expecting would be on the
397 classpath.
398 </warn>
399
400 <p>
401 <c>java-config</c> can also be used to set a system-wide default CLASSPATH, as
402 well a user-specific default CLASSPATH.
403 </p>
404
405 <p>
406 First, you will want to list available Java libraries installed on your system
407 that might want to be put in your CLASSPATH. Here is an example of output:
408 </p>
409
410 <pre caption="Listing classes">
411 # <i>java-config --list-available-packages</i>
412 [xerces-2] The next generation of high performance, fully compliant XML parsers in the Apache Xerces family (/usr/share/xerces-2/package.env)
413 [junit] Simple framework to write repeatable tests (/usr/share/junit/package.env)
414 [bsh] BeanShell: A small embeddable Java source interpreter (/usr/share/bsh/package.env)
415 [bcel] The Byte Code Engineering Library: analyze, create, manipulate Java class files (/usr/share/bcel/package.env)
416 [log4j] A low-overhead robust logging package for Java (/usr/share/log4j/package.env)
417 ...
418 </pre>
419
420 <p>
421 Again, the names in brackets (<e>[]</e>) are the IDs that you have to pass to
422 <c>java-config --set-system-classpath</c>. Here is an example:
423 </p>
424
425 <pre caption="Setting classpaths">
426 # <i>java-config --set-system-classpath log4j,xerces-2</i>
427 </pre>
428
429 <note>
430 The current directory (<path>.</path>) will not be part of the system
431 classpath, as that should be added in your system's login profile.
432 </note>
433
434 <p>
435 You will have to update your environment by logging out, then in again or
436 sourcing <path>/etc/profile</path>.
437 </p>
438
439 <p>
440 For users, <c>java-config --set-user-classpath</c> will create
441 <path>~/.gentoo/java-env-classpath</path>, which you should then source from
442 your shell's profile.
443 </p>
444
445 <pre caption="Sourcing user specific classpath">
446 <i>if [[ -f "${HOME}/.gentoo/java-env-classpath" ]]; then
447 source ${HOME}/.gentoo/java-env-classpath
448 fi</i>
449 </pre>
450
451 <p>
452 If you really want a system wide or user default classpath you can add
453 something like the following to your shell's profile. But we would advise
454 against it.
455 </p>
456
457 <pre caption="Setting classpath">
458 # <i>export CLASSPATH="${CLASSPATH}:$(java-config --classpath log4j,xerces-2)"</i>
459 </pre>
460
461 </body>
462 </section>
463 </chapter>
464
465 <chapter>
466 <title>Java Browser Plugins</title>
467 <section>
468 <title>Installing a plugin</title>
469 <body>
470
471 <p>
472 You can install a Java plugin for your web browser by emerging a Java VM with
473 the <c>nsplugin</c> USE flag set.
474 </p>
475
476 <note>
477 <c>nsplugin</c> is not available for all architectures. Check for available
478 plugins on your arch before trying to install a VM by running <c>emerge -pv
479 &lt;java-vm&gt;</c>.
480 </note>
481
482 <p>
483 Portage will allow you to install multiple versions of Java plugins, though
484 only one will be used by your browser. You can check the list of available
485 plugins by running:
486 </p>
487
488 <pre caption="Viewing available plugins">
489 # <i>eselect java-nsplugin list</i>
490 [1] sun-jre-bin-1.5
491 [2] blackdown-jre-1.4.2
492 </pre>
493
494 <p>
495 In this example, <c>sun-jre-bin</c> is selected for the browser plugin.
496 </p>
497
498 <pre caption="Selecting a plugin">
499 # <i>eselect java-nsplugin set sun-jre-bin-1.5</i>
500 </pre>
501
502 <p>
503 Verify that the correct plugin was selected:
504 </p>
505
506 <pre caption="Verifying the correct plugin">
507 # <i>eselect java-nsplugin list</i>
508 [1] sun-jre-bin-1.5 current
509 [2] blackdown-jre-1.4.2
510 </pre>
511
512 <p>
513 Java.com also provides a link to <uri
514 link="http://java.com/en/download/installed.jsp">verify your installed
515 plugin</uri>. Additionally, if you are using a Mozilla-based browser, you can
516 verify your Java plugin by typing <c>about:plugins</c> into the address bar.
517 </p>
518
519 </body>
520 </section>
521 <section>
522 <title>Plugins on multilib systems</title>
523 <body>
524
525 <p>
526 If you are running a mixed 64-bit and 32-bit multilib system (for example, on AMD64),
527 you can only use 32-bit Java plugins.
528 </p>
529
530 <p>
531 To use a 32-bit plugin, you will need to emerge <c>emul-linux-x86-java</c> with
532 the <c>nsplugin</c> USE flag enabled.
533 </p>
534
535 <pre caption="Installing a 32-bit plugin">
536 # <i>echo "app-emulation/emul-linux-x86-java nsplugin" >> /etc/portage/package.use</i>
537 # <i>emerge emul-linux-x86-java</i>
538 </pre>
539
540 <p>
541 Next, check which plugins are available:
542 </p>
543
544 <pre caption="Viewing available plugins">
545 # <i>eselect java-nsplugin list</i>
546 Available 32-bit Java browser plugins
547 [1] emul-linux-x86-java-1.4.2
548 [2] emul-linux-x86-java-1.5
549 </pre>
550
551 <p>
552 Although you must select a 32-bit browser (such as <c>mozilla-firefox-bin</c>)
553 to use with your 32-bit plugin, the 64-bit version of <c>konqueror</c> uses your
554 Java VM directly, so it's possible to use the 64-bit version of <c>blackdown</c>
555 with this browser; no further configuration is necessary.
556 </p>
557
558 <p>
559 Now select the right plugin for your 32-bit browser:
560 </p>
561
562 <pre caption="Selecting plugins">
563 # <i>eselect java-nsplugin set 32bit emul-linux-x86-java-1.5</i>
564 </pre>
565
566 <p>
567 Verify the correct plugin was selected:
568 </p>
569
570 <pre caption="Verifying the correct plugin">
571 # <i>eselect java-nsplugin list</i>
572 Available 32-bit Java browser plugins
573 [1] emul-linux-x86-java-1.4.2
574 [2] emul-linux-x86-java-1.5 current
575 </pre>
576
577 </body>
578 </section>
579 </chapter>
580
581 <chapter>
582 <title>USE flags for use with Java</title>
583 <section>
584 <title>Setting USE flags</title>
585 <body>
586
587 <p>
588 For more information regarding USE flags, refer to the <uri
589 link="/doc/en/handbook/handbook-x86.xml?part=2&amp;chap=2">USE flags</uri>
590 chapter from the Gentoo Handbook.
591 </p>
592
593 </body>
594 </section>
595 <section>
596 <title>The flags</title>
597 <body>
598
599 <ul>
600 <li>The <b>java</b> flag adds support for Java in a variety of programs</li>
601 <li>
602 The <b>nsplugin</b> flag adds support for Mozilla-like browsers (including
603 Firefox). You will need this for viewing Java applets in your Mozilla-like
604 browser.
605 </li>
606 <li>
607 The <b>source</b> flag installs a zip of the source code of a package.
608 This is traditionally used for IDEs to 'attach' source to the libraries you
609 are using.
610 </li>
611 <li>The <b>jce</b> flag adds support for the Java Cryptography Engine</li>
612 <li>
613 For Java packages, the <b>doc</b> flag will build API documentation using
614 javadoc.
615 </li>
616 </ul>
617
618 </body>
619 </section>
620 </chapter>
621
622 <chapter>
623 <title>Additional resources</title>
624 <section>
625 <title>Off-line resources</title>
626 <body>
627
628 <ul>
629 <li>java-config man page</li>
630 <li><c>java-config --help</c></li>
631 </ul>
632
633 </body>
634 </section>
635 <section>
636 <title>Online resources</title>
637 <body>
638
639 <ul>
640 <li>
641 The <uri link="http://www.gentoo.org/proj/en/java/">Java Project
642 Page</uri>
643 </li>
644 <li>
645 The <uri
646 link="http://news.gmane.org/gmane.linux.gentoo.java">gentoo-java</uri>,
647 <uri
648 link="http://news.gmane.org/gmane.linux.gentoo.user">gentoo-user</uri>, and
649 <uri
650 link="http://news.gmane.org/gmane.linux.gentoo.devel">gentoo-dev</uri>
651 mailing list archives
652 </li>
653 <li>#gentoo and #gentoo-java on irc.freenode.net</li>
654 <li>
655 <uri
656 link="http://en.wikipedia.org/wiki/Java_programming_language">Wikipedia's
657 entry for Java</uri>
658 </li>
659 <li>
660 If you have suggestions or questions regarding this document, please email
661 the Gentoo Java team: <mail>java@gentoo.org</mail>
662 </li>
663 </ul>
664
665 </body>
666 </section>
667 </chapter>
668 </guide>

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