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1 <?xml version="1.0" encoding="UTF-8"?>
2 <!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/java.xml,v 1.29 2006/08/09 20:44:33 rane 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>0.8</version>
28 <date>2006-08-30</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, plug-ins 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>New Java System</title>
61 <section>
62 <body>
63
64 <p>
65 The way Java is handled on Gentoo has recently seen many changes and
66 improvements. This has only happened very recently, and as a result, all the
67 packages related to it are marked with testing keywords, ie ~x86. This
68 document assumes you are using the new system.
69 </p>
70
71 </body>
72 </section>
73 <section>
74 <title>Keywords</title>
75 <body>
76
77 <p>
78 If you are using the stable tree opposed to ~arch, you will need to add some
79 entries to your <path>/etc/portage/package.keywords</path>:
80 </p>
81
82 <pre caption="package.keywords">
83 # Core Gentoo/Java Packages
84 dev-java/ant-core
85 dev-java/ant-tasks
86 dev-java/ant
87 dev-java/java-config
88 dev-java/java-config-wrapper
89 dev-java/javatoolkit
90 dev-java/sun-jce-bin
91 # JDKs
92 =dev-java/sun-jdk-1.4*
93 =dev-java/sun-jdk-1.5*
94 =dev-java/ibm-jdk-bin-1.4*
95 =dev-java/ibm-jdk-bin-1.5*
96 =dev-java/jrockit-jdk-bin-1.4*
97 =dev-java/jrockit-jdk-bin-1.5*
98 =dev-java/blackdown-jdk-1.4*
99 dev-java/kaffe
100 # JREs
101 =dev-java/sun-jre-bin-1.4*
102 =dev-java/sun-jre-bin-1.5*
103 =dev-java/ibm-jre-bin-1.4*
104 =dev-java/blackdown-jre-1.4*
105 # Virtuals
106 virtual/jdk
107 virtual/jre
108 # Compilers
109 dev-java/eclipse-ecj
110 dev-java/jikes
111 # Documentation
112 dev-java/java-sdk-docs
113 # Misc packages that have been updated to generation-2,
114 # where the generation-1 won't build and/or run properly
115 dev-java/lucene
116 # These have optional Java support, but need ~arch to function properly
117 # with generation-2
118 dev-util/subversion
119 sys-libs/db
120 </pre>
121
122 <warn>
123 It is crucial that you list ALL these packages in
124 <path>/etc/portage/package.keywords</path>, otherwise you will have problems in
125 the later steps of this guide. Your new Java system will not function correctly
126 without this list.
127 </warn>
128
129 </body>
130 </section>
131 <section>
132 <title>Existing installs</title>
133 <body>
134
135 <p>
136 For existing installs, regardless of if you have installed anything Java
137 before, make sure you have followed the <uri
138 link="/proj/en/java/java-upgrade.xml">Java Upgrade Guide</uri>.
139 </p>
140
141 </body>
142 </section>
143 <section>
144 <title>New installs</title>
145 <body>
146
147 <p>
148 New installs should require no further preparation.
149 </p>
150
151 </body>
152 </section>
153 </chapter>
154
155 <chapter>
156 <title>Installing a Virtual Machine</title>
157 <section>
158 <title>The choices</title>
159 <body>
160
161 <p>
162 Gentoo provides numerous Runtime Environments (JREs) and Development Kits
163 (JDKs). Among the current choices, we have:
164 </p>
165
166 <table>
167 <tr>
168 <th>Vendor</th>
169 <th>JDK</th>
170 <th>JRE</th>
171 </tr>
172 <tr>
173 <ti>The Blackdown Java Kit</ti>
174 <ti>dev-java/blackdown-jdk</ti>
175 <ti>dev-java/blackdown-jre</ti>
176 </tr>
177 <tr>
178 <ti>Sun's Java Kit</ti>
179 <ti>dev-java/sun-jdk</ti>
180 <ti>dev-java/sun-jre-bin</ti>
181 </tr>
182 <tr>
183 <ti>The IBM Java Kit</ti>
184 <ti>dev-java/ibm-jdk-bin</ti>
185 <ti>dev-java/ibm-jre-bin</ti>
186 </tr>
187 <tr>
188 <ti>The Compaq Java Kit for Alpha/Linux/GNU</ti>
189 <ti>dev-java/compaq-jdk</ti>
190 <ti>dev-java/compaq-jre</ti>
191 </tr>
192 <tr>
193 <ti>BEA WebLogic's J2SE Development Kit</ti>
194 <ti>dev-java/jrockit-jdk-bin</ti>
195 </tr>
196 </table>
197
198 <!--
199 TODO: list free implementations?
200 note about not drop-in replacements
201 kaffe/sablevm/gcj/jamvm
202 -->
203
204 <p>
205 The default is Blackdown for both the JRE and the JDK, as it is freely ("free
206 as in beer") available without any registration fuss.
207 </p>
208
209 <p>
210 The default for Java 1.4 is the Blackdown JRE/JDK pair, as it is freely
211 ("free as in beer") available without any registration fuss.
212 </p>
213
214 <p>
215 JREs and JDKs from Sun, IBM, and BEA are generally faster, but getting them
216 is a bit more work, as you are required to read and accept their license before
217 downloading (IBM additionally requires you to register).
218 </p>
219
220 </body>
221 </section>
222 <section>
223 <title>Installing a JRE/JDKs</title>
224 <body>
225
226 <p>
227 To install your profile's default JDK, you can run <c>emerge virtual/jdk</c>.
228 Or to install your profile's default JRE, you can <c>emerge virtual/jre</c>.
229 </p>
230
231 <p>
232 In recent events, Sun has relicensed their JDK and JRE under a more Linux
233 distro friendly license. As a result, Sun releases Java 1.5 and onwards are
234 freely downloadable, without any further hassle.
235 </p>
236
237 <note>
238 A JDK also includes a JRE, so if you install a JDK you shouldn't have to also
239 have to install a JRE.
240 </note>
241
242 </body>
243 </section>
244 <section>
245 <title>Installing fetch-restricted virtual machines</title>
246 <body>
247
248 <p>
249 As already mentioned, some of the JDKs and JREs require you to jump through a
250 few hoops before installing. Simply emerge the packages as you normally would.
251 The ebuilds will then instruct you where to go and what to download.
252 </p>
253
254 <p>
255 You should download the indicated file(s) into
256 <path>/usr/portage/distfiles</path>. Once there, you can rerun the emerge
257 command, at which point the JRE/JDK will be begin to install.
258 </p>
259
260 </body>
261 </section>
262 </chapter>
263
264 <chapter>
265 <title>Configuring your virtual machine</title>
266 <section>
267 <title>Overview</title>
268 <body>
269
270 <p>
271 Gentoo has the ability to have multiple JDKs and JREs installed without causing
272 conflicts.
273 </p>
274
275 <p>
276 Using the <c>java-config</c> tool, you can set the system-wide default
277 (provided you have root access). Users can also use <c>java-config</c> to set
278 up their own personal default.
279 </p>
280
281 <note>
282 You can also use <e>eselect</e> to change the system and user vm. See
283 <c>eselect java-vm help</c>.
284 </note>
285
286 </body>
287 </section>
288 <section>
289 <title>Setting a default virtual machine</title>
290 <body>
291
292 <p>
293 Running the command <c>java-config --list-available-vms</c> will give you a
294 list of all JREs and JDKs installed on your system. Here is an example of
295 output:
296 </p>
297
298 <pre caption="Listing available VMs">
299 # <i>java-config --list-available-vms</i>
300 1) Blackdown JDK 1.3.1 [blackdown-jdk-1.3] (/etc/env.d/java/20blackdown-jdk-1.3)
301 2) Blackdown JDK 1.4.2.02 [blackdown-jdk-1.4] (/etc/env.d/java/20blackdown-jdk-1.4)
302 3) Blackdown JRE 1.4.2.02 [blackdown-jre-1.4] (/etc/env.d/java/20blackdown-jre-1.4)
303 4) IBM JDK 1.4.2 [ibm-jdk-bin-1.4] (/etc/env.d/java/20ibm-jdk-bin-1.4)
304 5) IBM JRE 1.4.2 [ibm-jre-bin-1.4] (/etc/env.d/java/20ibm-jre-bin-1.4)
305 6) WebLogic JRockit 1.4.2.05 [jrockit-jdk-bin-1.4] (/etc/env.d/java/20jrockit-jdk-bin-1.4)
306 7) WebLogic JRockit 1.5.0.03 [jrockit-jdk-bin-1.5] (/etc/env.d/java/20jrockit-jdk-bin-1.5)
307 8) Sun JDK 1.3.1.13 [sun-jdk-1.3] (/etc/env.d/java/20sun-jdk-1.3)
308 9) Sun JDK 1.4.2.09 [sun-jdk-1.4] (/etc/env.d/java/20sun-jdk-1.4)
309 *) Sun JDK 1.5.0.04 [sun-jdk-1.5] (/etc/env.d/java/20sun-jdk-1.5)
310 11) Sun JRE 1.4.2.09 [sun-jre-bin-1.4] (/etc/env.d/java/20sun-jre-bin-1.4)
311 12) Sun JRE 1.5.0.04 [sun-jre-bin-1.5] (/etc/env.d/java/20sun-jre-bin-1.5)
312 </pre>
313
314 <p>
315 The <e>*</e> indicates this is the current active vm (system-vm or user-vm when
316 set). The name in the brackets (<e>[]</e>) is the handle or ID for that
317 particular VM. You use the handle or the number to <c>java-config
318 --set-system-vm</c>. Here is an example of how to set the system VM.
319 </p>
320
321 <pre caption="Setting the System VM">
322 <comment>(By handle (preferred))</comment>
323 # <i>java-config --set-system-vm blackdown-jdk-1.4</i>
324 <comment>(By number)</comment>
325 # <i>java-config --set-system-vm 2</i>
326 </pre>
327
328 <p>
329 As a regular user, you can use <c>java-config --set-user-vm</c>.
330 </p>
331
332 <note>
333 You no longer have to <c>source</c> the profile for updates to the user/system
334 VM take place.
335 </note>
336
337 </body>
338 </section>
339 <section id="preferred-vm">
340 <title>Preferred VM</title>
341 <body>
342
343 <p>
344 While merging Java packages, the VM can and will be switched as necessary.
345 </p>
346
347 <p>
348 Because of the wide variety of available VMs, we do not have the resources to
349 test and verify every package works on all of them. So to ensure that every
350 packages merges smoothly, we have defined a list of <e>default/supported
351 VMs</e> per arch. You can find them in
352 <path>/usr/share/java-config/config/jdk-defaults.conf</path>. When you are
353 merging a Java package, and it detects one of the VM in that file is installed,
354 it will automatically use that VM, instead of the system-vm.
355 </p>
356
357 <p>
358 The merge time VM switching is also needed when, for example, your system-vm is
359 set a 1.4 VM and the package you are merging requires a 1.5 VM. While merging
360 it will use the preferred 1.5 VM, leaving your system-vm choice intact.
361 </p>
362
363 <p>
364 Of course, Gentoo is all about choice, so you can override these defaults in
365 <path>/etc/java-config-2/build/jdk.conf</path> and have complete control over
366 which VM will get used. Some examples:
367 </p>
368
369 <pre caption="Example /etc/java-config-2/build/jdk.conf">
370 <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>
371 *=sun-jdk
372 </pre>
373
374 <pre caption="Example /etc/java-config-2/build/jdk.conf">
375 <comment>(Always use sun-jdk-1.5 wherever possible, except for when a 1.4 or 1.3 VM is explicitly required)</comment>
376 *=sun-jdk-1.5
377 </pre>
378
379 <pre caption="Example /etc/java-config-2/build/jdk.conf">
380 <comment># For 1.3 I prefer sun-jdk 1.4 but when it is not available, use ibm-jdk-bin,
381 # For 1.4, use blackdown-jdk, and for 1.5, use sun-jdk </comment>
382 1.3=sun-jdk-1.4 ibm-jdk-bin
383 1.4=blackdown-jdk
384 1.5=sun-jdk
385 </pre>
386
387 <warn>
388 You do not have to edit this file. If you change these options to use a
389 unsupported VM, things could possibly break. Bugs reported with a unsupported
390 VM won't be prioritized as much as bugs present within supported VMs.
391 </warn>
392
393 </body>
394 </section>
395 </chapter>
396
397 <chapter>
398 <title>Compilers</title>
399 <section>
400 <body>
401
402 <p>
403 The standard Java compiler used for building is javac, which comes with each
404 JDK. In addition to configuring the VM used at build time, it is also possible
405 configure which compiler is used. Essentially, you define a list your
406 preference for which compiler to use in
407 <path>/etc/java-config-2/build/compilers.conf</path>.
408 </p>
409
410 <pre caption="/etc/java-config-2/build/compilers.conf">
411 # If the ebuild supports it
412 # it will check the COMPILERS var front to back and
413 # use the first compiler that is installed
414
415 COMPILERS="ecj-3.1 jikes javac"
416 </pre>
417
418 <p>
419 Some compilers don't support all possible -target and -source arguments.
420 Therefore, each compiler in the list is checked to see if it can support the
421 desired -source/-target. javac will work in all cases, so if no other suitable
422 compiler is found, it will be used instead.
423 </p>
424
425 <p>
426 More details about each compiler are provided below:
427 </p>
428
429 <table>
430 <tr>
431 <th>Name</th>
432 <th>Handle</th>
433 <th>Package</th>
434 <th>Description</th>
435 </tr>
436 <tr>
437 <ti>javac</ti>
438 <ti>javac</ti>
439 <ti>N/A</ti>
440 <ti>
441 This is the default compiler that will be used, and comes with each JDK.
442 </ti>
443 </tr>
444 <tr>
445 <ti>jikes</ti>
446 <ti>jikes</ti>
447 <ti>dev-java/jikes</ti>
448 <ti>
449 Jikes was originally developed by IBM. Anecdotally, it is generally quicker
450 than javac. Note however, that it is more pedantic, and will fail under a
451 few circumstances where javac has no issue. It also does not support Java
452 1.5 syntax yet.
453 </ti>
454 </tr>
455 <tr>
456 <ti>Eclipse Compiler for Java</ti>
457 <ti>ecj-3.1</ti>
458 <ti>=dev-java/eclipse-ecj-3.1*</ti>
459 <ti>
460 ECJ is the compiler used by the Eclipse software development kit. It is
461 very full featured, and is pretty fast. It does support Java 1.5 syntax.
462 </ti>
463 </tr>
464 </table>
465
466 </body>
467 </section>
468 </chapter>
469
470 <chapter>
471 <title>Setting a default CLASSPATH</title>
472 <section>
473 <body>
474
475 <warn>
476 The options explained in this section should be considered deprecated and will
477 most likely be removed in the future. We strongly recommend against using
478 these, because your Java projects or application should ideally manage their
479 own classpaths. If you choose to specify a default CLASSPATH, some applications
480 may behave unexpectedly, because classes they weren't expecting would be on the
481 classpath.
482 </warn>
483
484 <p>
485 <c>java-config</c> can also be used to set a system-wide default CLASSPATH, as
486 well a user-specific default CLASSPATH.
487 </p>
488
489 <p>
490 First, you will want to list available Java libraries installed on your system
491 that might want to be put in your CLASSPATH. Here is an example of output:
492 </p>
493
494 <pre caption="Listing classes">
495 # <i>java-config --list-available-packages</i>
496 [xerces-2] The next generation of high performance, fully compliant XML parsers in the Apache Xerces family (/usr/share/xerces-2/package.env)
497 [junit] Simple framework to write repeatable tests (/usr/share/junit/package.env)
498 [bsh] BeanShell: A small embeddable Java source interpreter (/usr/share/bsh/package.env)
499 [bcel] The Byte Code Engineering Library: analyze, create, manipulate Java class files (/usr/share/bcel/package.env)
500 [log4j] A low-overhead robust logging package for Java (/usr/share/log4j/package.env)
501 ...
502 </pre>
503
504 <p>
505 Again, the names in brackets (<e>[]</e>) are the IDs that you have to pass to
506 <c>java-config --set-system-classpath</c>. Here is an example:
507 </p>
508
509 <pre caption="Setting classpaths">
510 # <i>java-config --set-system-classpath log4j,xerces-2</i>
511 </pre>
512
513 <note>
514 The current directory (<path>.</path>) will not be part of the system
515 classpath, as that should be added in your system's login profile.
516 </note>
517
518 <p>
519 You will have to update your environment by logging out, then in again or
520 sourcing <path>/etc/profile</path>.
521 </p>
522
523 <p>
524 For users, <c>java-config --set-user-classpath</c> will create
525 <path>~/.gentoo/java-env-classpath</path>, which you should then source from
526 your shell's profile.
527 </p>
528
529 <pre caption="Sourcing user specific classpath">
530 <i>if [[ -f "${HOME}/.gentoo/java-env-classpath" ]]; then
531 source ${HOME}/.gentoo/java-env-classpath
532 fi</i>
533 </pre>
534
535 <p>
536 If you really want a system wide or user default classpath you can add
537 something like the following to your shell's profile. But we would advise
538 against it.
539 </p>
540
541 <pre caption="Setting classpath">
542 # <i>export CLASSPATH="${CLASSPATH}:$(java-config --classpath log4j,xerces-2)"</i>
543 </pre>
544
545 </body>
546 </section>
547 </chapter>
548
549 <chapter>
550 <title>USE flags for use with Java</title>
551 <section>
552 <title>Setting USE flags</title>
553 <body>
554
555 <p>
556 For more information regarding USE flags, refer to the <uri
557 link="/doc/en/handbook/handbook-x86.xml?part=2&amp;chap=2">USE flags</uri>
558 chapter from the Gentoo Handbook.
559 </p>
560
561 </body>
562 </section>
563 <section>
564 <title>The flags</title>
565 <body>
566
567 <ul>
568 <li>The <b>java</b> flag adds support for Java in a variety of programs</li>
569 <li>
570 The <b>nsplugin</b> flag adds support for Mozilla-like browsers (including
571 Firefox).You will need this for viewing Java applets in your Mozilla-like
572 browser.
573 </li>
574 <li>
575 The <b>doc</b> flag will typically install API documentation, as generated
576 by javadoc.
577 </li>
578 <li>
579 The <b>source</b> flag will install a zip of the package's source code.
580 This is typically used to provide your IDE with the source code for the
581 package.
582 </li>
583 <li>
584 The <b>source</b> flag installs a zip of the source code of a package.
585 This is traditionally used for for IDEs to 'attach' source to the libraries
586 you are using.
587 </li>
588 <li>
589 For Java packages, the <b>doc</b> flag will build API documentation using
590 javadoc.
591 </li>
592 </ul>
593
594 </body>
595 </section>
596 </chapter>
597
598 <chapter>
599 <title>Additional resources</title>
600 <section>
601 <title>Off-line resources</title>
602 <body>
603
604 <ul>
605 <li>java-config man page</li>
606 <li><c>java-config --help</c></li>
607 </ul>
608
609 </body>
610 </section>
611 <section>
612 <title>Online resources</title>
613 <body>
614
615 <ul>
616 <li>
617 The <uri link="http://www.gentoo.org/proj/en/java/">Java Project
618 Page</uri>
619 </li>
620 <li>
621 The <uri
622 link="http://news.gmane.org/gmane.linux.gentoo.java">gentoo-java</uri>,
623 <uri
624 link="http://news.gmane.org/gmane.linux.gentoo.user">gentoo-user</uri>, and
625 <uri
626 link="http://news.gmane.org/gmane.linux.gentoo.devel">gentoo-dev</uri>
627 mailing list archives
628 </li>
629 <li>#gentoo and #gentoo-java on irc.freenode.net</li>
630 <li>
631 <uri
632 link="http://en.wikipedia.org/wiki/Java_programming_language">Wikipedia's
633 entry for Java</uri>
634 </li>
635 </ul>
636
637 </body>
638 </section>
639 </chapter>
640 </guide>

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