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1 <?xml version="1.0" encoding="UTF-8"?>
2 <!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/java.xml,v 1.27 2006/07/25 08:13:47 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>0.6</version>
28 <date>2006-08-07</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, i.e. x86, ppc, or amd64 as opposed to ~x86,
79 ~ppc, or ~amd64, you will need to add some entries to your
80 <path>/etc/portage/package.keywords</path>:
81 </p>
82
83 <pre caption="package.keywords">
84 # Core Gentoo/Java Packages
85 dev-java/ant-core
86 dev-java/ant-tasks
87 dev-java/ant
88 dev-java/java-config
89 dev-java/java-config-wrapper
90 dev-java/javatoolkit
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 <impo>
123 It is crucial that you keyword ALL packages related to the new Java system,
124 otherwise you will have problems in the later steps of this guide.
125 </impo>
126
127 <impo>
128 It can't be emphasized enough that you have to have ALL the packages related
129 to the new Java system keyworded for it to function properly.
130 </impo>
131
132 </body>
133 </section>
134 <section>
135 <title>Existing installs</title>
136 <body>
137
138 <p>
139 For existing installs, regardless of if you have installed anything Java
140 before, make sure you have followed the <uri
141 link="/proj/en/java/java-upgrade.xml">Java Upgrade Guide</uri>.
142 </p>
143
144 </body>
145 </section>
146 <section>
147 <title>New installs</title>
148 <body>
149
150 <p>
151 New installs should require no further preparation.
152 </p>
153
154 </body>
155 </section>
156 </chapter>
157
158 <chapter>
159 <title>Installing a Virtual Machine</title>
160 <section>
161 <title>The choices</title>
162 <body>
163
164 <p>
165 Gentoo provides numerous Runtime Environments (JREs) and Development Kits
166 (JDKs). Among the current choices, we have:
167 </p>
168
169 <table>
170 <tr>
171 <th>Vendor</th>
172 <th>JDK</th>
173 <th>JRE</th>
174 </tr>
175 <tr>
176 <ti>The Blackdown Java Kit</ti>
177 <ti>dev-java/blackdown-jdk</ti>
178 <ti>dev-java/blackdown-jre</ti>
179 </tr>
180 <tr>
181 <ti>Sun's Java Kit</ti>
182 <ti>dev-java/sun-jdk</ti>
183 <ti>dev-java/sun-jre-bin</ti>
184 </tr>
185 <tr>
186 <ti>The IBM Java Kit</ti>
187 <ti>dev-java/ibm-jdk-bin</ti>
188 <ti>dev-java/ibm-jre-bin</ti>
189 </tr>
190 <tr>
191 <ti>The Compaq Java Kit for Alpha/Linux/GNU</ti>
192 <ti>dev-java/compaq-jdk</ti>
193 <ti>dev-java/compaq-jre</ti>
194 </tr>
195 <tr>
196 <ti>BEA WebLogic's J2SE Development Kit</ti>
197 <ti>dev-java/jrockit-jdk-bin</ti>
198 </tr>
199 </table>
200
201 <!--
202 TODO: list free implementations?
203 note about not drop-in replacements
204 kaffe/sablevm/gcj/jamvm
205 -->
206
207 <p>
208 The default is Blackdown for both the JRE and the JDK, as it is freely ("free
209 as in beer") available without any registration fuss.
210 </p>
211
212 <p>
213 The default for Java 1.4 is the Blackdown JRE/JDK pair, as it is freely
214 ("free as in beer") available without any registration fuss.
215 </p>
216
217 <p>
218 JREs and JDKs from Sun, IBM, and BEA are generally faster, but getting them
219 is a bit more work, as you are required to read and accept their license before
220 downloading (IBM additionally requires you to register).
221 </p>
222
223 </body>
224 </section>
225 <section>
226 <title>Installing a JRE/JDKs</title>
227 <body>
228
229 <p>
230 To install your profile's default JDK, you can run <c>emerge virtual/jdk</c>.
231 Or to install your profile's default JRE, you can <c>emerge virtual/jre</c>.
232 </p>
233
234 <p>
235 In recent events, Sun has relicensed their JDK and JRE under a more Linux
236 distro friendly license. As a result, Sun releases Java 1.5 and onwards are
237 freely downloadable, without any further hassle.
238 </p>
239
240 <note>
241 A JDK also includes a JRE, so if you install a JDK you shouldn't have to also
242 have to install a JRE.
243 </note>
244
245 </body>
246 </section>
247 <section>
248 <title>Installing fetch-restricted virtual machines</title>
249 <body>
250
251 <p>
252 As already mentioned, some of the JDKs and JREs require you to jump through a
253 few hoops before installing. Simply emerge the packages as you normally would.
254 The ebuilds will then instruct you where to go and what to download.
255 </p>
256
257 <p>
258 You should download the indicated file(s) into
259 <path>/usr/portage/distfiles</path>. Once there, you can rerun the emerge
260 command, at which point the JRE/JDK will be begin to install.
261 </p>
262
263 </body>
264 </section>
265 </chapter>
266
267 <chapter>
268 <title>Configuring your virtual machine</title>
269 <section>
270 <title>Overview</title>
271 <body>
272
273 <p>
274 Gentoo has the ability to have multiple JDKs and JREs installed without causing
275 conflicts.
276 </p>
277
278 <p>
279 Using the <c>java-config</c> tool, you can set the system-wide default
280 (provided you have root access). Users can also use <c>java-config</c> to set
281 up their own personal default.
282 </p>
283
284 <note>
285 You can also use <e>eselect</e> to change the system and user vm. See
286 <c>eselect java-vm help</c>.
287 </note>
288
289 </body>
290 </section>
291 <section>
292 <title>Setting a default virtual machine</title>
293 <body>
294
295 <p>
296 Running the command <c>java-config --list-available-vms</c> will give you a
297 list of all JREs and JDKs installed on your system. Here is an example of
298 output:
299 </p>
300
301 <pre caption="Listing available VMs">
302 # <i>java-config --list-available-vms</i>
303 1) Blackdown JDK 1.3.1 [blackdown-jdk-1.3] (/etc/env.d/java/20blackdown-jdk-1.3)
304 2) Blackdown JDK 1.4.2.02 [blackdown-jdk-1.4] (/etc/env.d/java/20blackdown-jdk-1.4)
305 3) Blackdown JRE 1.4.2.02 [blackdown-jre-1.4] (/etc/env.d/java/20blackdown-jre-1.4)
306 4) IBM JDK 1.4.2 [ibm-jdk-bin-1.4] (/etc/env.d/java/20ibm-jdk-bin-1.4)
307 5) IBM JRE 1.4.2 [ibm-jre-bin-1.4] (/etc/env.d/java/20ibm-jre-bin-1.4)
308 6) WebLogic JRockit 1.4.2.05 [jrockit-jdk-bin-1.4] (/etc/env.d/java/20jrockit-jdk-bin-1.4)
309 7) WebLogic JRockit 1.5.0.03 [jrockit-jdk-bin-1.5] (/etc/env.d/java/20jrockit-jdk-bin-1.5)
310 8) Sun JDK 1.3.1.13 [sun-jdk-1.3] (/etc/env.d/java/20sun-jdk-1.3)
311 9) Sun JDK 1.4.2.09 [sun-jdk-1.4] (/etc/env.d/java/20sun-jdk-1.4)
312 *) Sun JDK 1.5.0.04 [sun-jdk-1.5] (/etc/env.d/java/20sun-jdk-1.5)
313 11) Sun JRE 1.4.2.09 [sun-jre-bin-1.4] (/etc/env.d/java/20sun-jre-bin-1.4)
314 12) Sun JRE 1.5.0.04 [sun-jre-bin-1.5] (/etc/env.d/java/20sun-jre-bin-1.5)
315 </pre>
316
317 <p>
318 The <e>*</e> indicates this is the current active vm (system-vm or user-vm when
319 set). The name in the brackets (<e>[]</e>) is the handle or ID for that
320 particular VM. You use the handle or the number to <c>java-config
321 --set-system-vm</c>. Here is an example of how to set the system VM.
322 </p>
323
324 <pre caption="Setting the System VM">
325 <comment>(By handle (preferred))</comment>
326 # <i>java-config --set-system-vm blackdown-jdk-1.4</i>
327 <comment>(By number)</comment>
328 # <i>java-config --set-system-vm 2</i>
329 </pre>
330
331 <p>
332 As a regular user, you can use <c>java-config --set-user-vm</c>.
333 </p>
334
335 <note>
336 You no longer have to <c>source</c> the profile for updates to the user/system
337 VM take place.
338 </note>
339
340 </body>
341 </section>
342 <section id="preferred-vm">
343 <title>Preferred VM</title>
344 <body>
345
346 <p>
347 While merging Java packages, the VM can and will be switched as necessary.
348 </p>
349
350 <p>
351 Because of the wide variety of available VMs, we do not have the resources to
352 test and verify every package works on all of them. So to ensure that every
353 packages merges smoothly, we have defined a list of <e>default/supported
354 VMs</e> per arch. You can find them in
355 <path>/usr/share/java-config/config/jdk-defaults.conf</path>. When you are
356 merging a Java package, and it detects one of the VM in that file is installed,
357 it will automatically use that VM, instead of the system-vm.
358 </p>
359
360 <p>
361 The merge time VM switching is also needed when, for example, your system-vm is
362 set a 1.4 VM and the package you are merging requires a 1.5 VM. While merging
363 it will use the preferred 1.5 VM, leaving your system-vm choice intact.
364 </p>
365
366 <p>
367 Of course, Gentoo is all about choice, so you can override these defaults in
368 <path>/etc/java-config-2/build/jdk.conf</path> and have complete control over
369 which VM will get used. Some examples:
370 </p>
371
372 <pre caption="Example /etc/java-config-2/build/jdk.conf">
373 <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>
374 *=sun-jdk
375 </pre>
376
377 <pre caption="Example /etc/java-config-2/build/jdk.conf">
378 <comment>(Always use sun-jdk-1.5 wherever possible, except for when a 1.4 or 1.3 VM is explicitly required)</comment>
379 *=sun-jdk-1.5
380 </pre>
381
382 <pre caption="Example /etc/java-config-2/build/jdk.conf">
383 <comment># For 1.3 I prefer sun-jdk 1.4 but when it is not available, use ibm-jdk-bin,
384 # For 1.4, use blackdown-jdk, and for 1.5, use sun-jdk </comment>
385 1.3=sun-jdk-1.4 ibm-jdk-bin
386 1.4=blackdown-jdk
387 1.5=sun-jdk
388 </pre>
389
390 <warn>
391 You do not have to edit this file. If you change these options to use a
392 unsupported VM, things could possibly break. Bugs reported with a unsupported
393 VM won't be prioritized as much as bugs present within supported VMs.
394 </warn>
395
396 </body>
397 </section>
398 </chapter>
399
400 <chapter>
401 <title>Compilers</title>
402 <section>
403 <body>
404
405 <p>
406 The standard Java compiler used for building is javac, which comes with each
407 JDK. In addition to configuring the VM used at build time, it is also possible
408 configure which compiler is used. Essentially, you define a list your
409 preference for which compiler to use in
410 <path>/etc/java-config-2/build/compilers.conf</path>.
411 </p>
412
413 <pre caption="/etc/java-config-2/build/compilers.conf">
414 # If the ebuild supports it
415 # it will check the COMPILERS var front to back and
416 # use the first compiler that is installed
417
418 COMPILERS="ecj-3.1 jikes javac"
419 </pre>
420
421 <p>
422 Some compilers don't support all possible -target and -source arguments.
423 Therefore, each compiler in the list is checked to see if it can support the
424 desired -source/-target. javac will work in all cases, so if no other suitable
425 compiler is found, it will be used instead.
426 </p>
427
428 <p>
429 More details about each compiler are provided below:
430 </p>
431
432 <table>
433 <tr>
434 <th>Name</th>
435 <th>Handle</th>
436 <th>Package</th>
437 <th>Description</th>
438 </tr>
439 <tr>
440 <ti>javac</ti>
441 <ti>javac</ti>
442 <ti>N/A</ti>
443 <ti>
444 This is the default compiler that will be used, and comes with each JDK.
445 </ti>
446 </tr>
447 <tr>
448 <ti>jikes</ti>
449 <ti>jikes</ti>
450 <ti>dev-java/jikes</ti>
451 <ti>
452 Jikes was originally developed by IBM. Anecdotally, it is generally quicker
453 than javac. Note however, that it is more pedantic, and will fail under a
454 few circumstances where javac has no issue. It also does not support Java
455 1.5 syntax yet.
456 </ti>
457 </tr>
458 <tr>
459 <ti>Eclipse Compiler for Java</ti>
460 <ti>ecj-3.1</ti>
461 <ti>=dev-java/eclipse-ecj-3.1*</ti>
462 <ti>
463 ECJ is the compiler used by the Eclipse software development kit. It is
464 very full featured, and is pretty fast. It does support Java 1.5 syntax.
465 </ti>
466 </tr>
467 </table>
468
469 </body>
470 </section>
471 </chapter>
472
473 <chapter>
474 <title>Setting a default CLASSPATH</title>
475 <section>
476 <body>
477
478 <warn>
479 The options explained in this section should be considered deprecated and will
480 most likely be removed in the future. We strongly recommend against using
481 these, because your Java projects or application should ideally manage their
482 own classpaths. If you choose to specify a default CLASSPATH, some applications
483 may behave unexpectedly, because classes they weren't expecting would be on the
484 classpath.
485 </warn>
486
487 <p>
488 <c>java-config</c> can also be used to set a system-wide default CLASSPATH, as
489 well a user-specific default CLASSPATH.
490 </p>
491
492 <p>
493 First, you will want to list available Java libraries installed on your system
494 that might want to be put in your CLASSPATH. Here is an example of output:
495 </p>
496
497 <pre caption="Listing classes">
498 # <i>java-config --list-available-packages</i>
499 [xerces-2] The next generation of high performance, fully compliant XML parsers in the Apache Xerces family (/usr/share/xerces-2/package.env)
500 [junit] Simple framework to write repeatable tests (/usr/share/junit/package.env)
501 [bsh] BeanShell: A small embeddable Java source interpreter (/usr/share/bsh/package.env)
502 [bcel] The Byte Code Engineering Library: analyze, create, manipulate Java class files (/usr/share/bcel/package.env)
503 [log4j] A low-overhead robust logging package for Java (/usr/share/log4j/package.env)
504 ...
505 </pre>
506
507 <p>
508 Again, the names in brackets (<e>[]</e>) are the IDs that you have to pass to
509 <c>java-config --set-system-classpath</c>. Here is an example:
510 </p>
511
512 <pre caption="Setting classpaths">
513 # <i>java-config --set-system-classpath log4j,xerces-2</i>
514 </pre>
515
516 <note>
517 The current directory (<path>.</path>) will not be part of the system
518 classpath, as that should be added in your system's login profile.
519 </note>
520
521 <p>
522 You will have to update your environment by logging out, then in again or
523 sourcing <path>/etc/profile</path>.
524 </p>
525
526 <p>
527 For users, <c>java-config --set-user-classpath</c> will create
528 <path>~/.gentoo/java-env-classpath</path>, which you should then source from
529 your shell's profile.
530 </p>
531
532 <pre caption="Sourcing user specific classpath">
533 <i>if [[ -f "${HOME}/.gentoo/java-env-classpath" ]]; then
534 source ${HOME}/.gentoo/java-env-classpath
535 fi</i>
536 </pre>
537
538 <p>
539 If you really want a system wide or user default classpath you can add
540 something like the following to your shell's profile. But we would advise
541 against it.
542 </p>
543
544 <pre caption="Setting classpath">
545 # <i>export CLASSPATH="${CLASSPATH}:$(java-config --classpath log4j,xerces-2)"</i>
546 </pre>
547
548 </body>
549 </section>
550 </chapter>
551
552 <chapter>
553 <title>USE flags for use with Java</title>
554 <section>
555 <title>Setting USE flags</title>
556 <body>
557
558 <p>
559 For more information regarding USE flags, refer to the <uri
560 link="/doc/en/handbook/handbook-x86.xml?part=2&amp;chap=2">USE flags</uri>
561 chapter from the Gentoo Handbook.
562 </p>
563
564 </body>
565 </section>
566 <section>
567 <title>The flags</title>
568 <body>
569
570 <ul>
571 <li>The <b>java</b> flag adds support for Java in a variety of programs</li>
572 <li>
573 The <b>nsplugin</b> flag adds support for Mozilla-like browsers (including
574 Firefox).You will need this for viewing Java applets in your Mozilla-like
575 browser.
576 </li>
577 <li>
578 The <b>doc</b> flag will typically install API documentation, as generated
579 by javadoc.
580 </li>
581 <li>
582 The <b>source</b> flag will install a zip of the package's source code.
583 This is typically used to provide your IDE with the source code for the
584 package.
585 </li>
586 <li>
587 The <b>source</b> flag installs a zip of the source code of a package.
588 This is traditionally used for for IDEs to 'attach' source to the libraries
589 you are using.
590 </li>
591 <li>
592 For Java packages, the <b>doc</b> flag will build API documentation using
593 javadoc.
594 </li>
595 </ul>
596
597 </body>
598 </section>
599 </chapter>
600
601 <chapter>
602 <title>Additional resources</title>
603 <section>
604 <title>Off-line resources</title>
605 <body>
606
607 <ul>
608 <li>java-config man page</li>
609 <li><c>java-config --help</c></li>
610 </ul>
611
612 </body>
613 </section>
614 <section>
615 <title>Online resources</title>
616 <body>
617
618 <ul>
619 <li>
620 The <uri link="http://www.gentoo.org/proj/en/java/">Java Project
621 Page</uri>
622 </li>
623 <li>
624 The <uri
625 link="http://news.gmane.org/gmane.linux.gentoo.java">gentoo-java</uri>,
626 <uri
627 link="http://news.gmane.org/gmane.linux.gentoo.user">gentoo-user</uri>, and
628 <uri
629 link="http://news.gmane.org/gmane.linux.gentoo.devel">gentoo-dev</uri>
630 mailing list archives
631 </li>
632 <li>#gentoo and #gentoo-java on irc.freenode.net</li>
633 <li>
634 <uri
635 link="http://en.wikipedia.org/wiki/Java_programming_language">Wikipedia's
636 entry for Java</uri>
637 </li>
638 </ul>
639
640 </body>
641 </section>
642 </chapter>
643 </guide>

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