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1 <?xml version="1.0" encoding="UTF-8"?>
2 <!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/java.xml,v 1.31 2006/09/08 10:49:38 fox2mike 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>0.9</version>
28 <date>2006-09-10</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 <p>
204 The default for Java 1.4 is the Blackdown JRE/JDK pair, as it is freely
205 ("free as in beer") available without any registration fuss.
206 </p>
207
208 <p>
209 JREs and JDKs from Sun, IBM, and BEA are generally faster, but getting them
210 is a bit more work, as you are required to read and accept their license before
211 downloading (IBM additionally requires you to register).
212 </p>
213
214 </body>
215 </section>
216 <section>
217 <title>Installing a JRE/JDKs</title>
218 <body>
219
220 <p>
221 To install your profile's default JDK, you can run <c>emerge virtual/jdk</c>.
222 Or to install your profile's default JRE, you can <c>emerge virtual/jre</c>.
223 </p>
224
225 <p>
226 In recent events, Sun has relicensed their JDK and JRE under a more Linux
227 distro friendly license. As a result, Sun releases Java 1.5 and onwards are
228 freely downloadable, without any further hassle.
229 </p>
230
231 <note>
232 A JDK also includes a JRE, so if you install a JDK you shouldn't have to also
233 have to install a JRE.
234 </note>
235
236 </body>
237 </section>
238 <section>
239 <title>Installing fetch-restricted virtual machines</title>
240 <body>
241
242 <p>
243 As already mentioned, some of the JDKs and JREs require you to jump through a
244 few hoops before installing. Simply emerge the packages as you normally would.
245 The ebuilds will then instruct you where to go and what to download.
246 </p>
247
248 <p>
249 You should download the indicated file(s) into
250 <path>/usr/portage/distfiles</path>. Once there, you can rerun the emerge
251 command, at which point the JRE/JDK will be begin to install.
252 </p>
253
254 </body>
255 </section>
256 </chapter>
257
258 <chapter>
259 <title>Configuring your virtual machine</title>
260 <section>
261 <title>Overview</title>
262 <body>
263
264 <p>
265 Gentoo has the ability to have multiple JDKs and JREs installed without causing
266 conflicts.
267 </p>
268
269 <p>
270 Using the <c>java-config</c> tool, you can set the system-wide default
271 (provided you have root access). Users can also use <c>java-config</c> to set
272 up their own personal default.
273 </p>
274
275 <note>
276 You can also use <e>eselect</e> to change the system and user vm. See
277 <c>eselect java-vm help</c>.
278 </note>
279
280 </body>
281 </section>
282 <section>
283 <title>Setting a default virtual machine</title>
284 <body>
285
286 <p>
287 Running the command <c>java-config --list-available-vms</c> will give you a
288 list of all JREs and JDKs installed on your system. Here is an example of
289 output:
290 </p>
291
292 <pre caption="Listing available VMs">
293 # <i>java-config --list-available-vms</i>
294 1) Blackdown JDK 1.3.1 [blackdown-jdk-1.3] (/etc/env.d/java/20blackdown-jdk-1.3)
295 2) Blackdown JDK 1.4.2.02 [blackdown-jdk-1.4] (/etc/env.d/java/20blackdown-jdk-1.4)
296 3) Blackdown JRE 1.4.2.02 [blackdown-jre-1.4] (/etc/env.d/java/20blackdown-jre-1.4)
297 4) IBM JDK 1.4.2 [ibm-jdk-bin-1.4] (/etc/env.d/java/20ibm-jdk-bin-1.4)
298 5) IBM JRE 1.4.2 [ibm-jre-bin-1.4] (/etc/env.d/java/20ibm-jre-bin-1.4)
299 6) WebLogic JRockit 1.4.2.05 [jrockit-jdk-bin-1.4] (/etc/env.d/java/20jrockit-jdk-bin-1.4)
300 7) WebLogic JRockit 1.5.0.03 [jrockit-jdk-bin-1.5] (/etc/env.d/java/20jrockit-jdk-bin-1.5)
301 8) Sun JDK 1.3.1.13 [sun-jdk-1.3] (/etc/env.d/java/20sun-jdk-1.3)
302 9) Sun JDK 1.4.2.09 [sun-jdk-1.4] (/etc/env.d/java/20sun-jdk-1.4)
303 *) Sun JDK 1.5.0.04 [sun-jdk-1.5] (/etc/env.d/java/20sun-jdk-1.5)
304 11) Sun JRE 1.4.2.09 [sun-jre-bin-1.4] (/etc/env.d/java/20sun-jre-bin-1.4)
305 12) Sun JRE 1.5.0.04 [sun-jre-bin-1.5] (/etc/env.d/java/20sun-jre-bin-1.5)
306 </pre>
307
308 <p>
309 The <e>*</e> indicates this is the current active vm (system-vm or user-vm when
310 set). The name in the brackets (<e>[]</e>) is the handle or ID for that
311 particular VM. You use the handle or the number to <c>java-config
312 --set-system-vm</c>. Here is an example of how to set the system VM.
313 </p>
314
315 <pre caption="Setting the System VM">
316 <comment>(By handle (preferred))</comment>
317 # <i>java-config --set-system-vm blackdown-jdk-1.4</i>
318 <comment>(By number)</comment>
319 # <i>java-config --set-system-vm 2</i>
320 </pre>
321
322 <p>
323 As a regular user, you can use <c>java-config --set-user-vm</c>.
324 </p>
325
326 <note>
327 You no longer have to <c>source</c> the profile for updates to the user/system
328 VM take place.
329 </note>
330
331 </body>
332 </section>
333 <section id="preferred-vm">
334 <title>Preferred VM</title>
335 <body>
336
337 <p>
338 While merging Java packages, the VM can and will be switched as necessary.
339 </p>
340
341 <p>
342 Because of the wide variety of available VMs, we do not have the resources to
343 test and verify every package works on all of them. So to ensure that every
344 packages merges smoothly, we have defined a list of <e>default/supported
345 VMs</e> per arch. You can find them in
346 <path>/usr/share/java-config/config/jdk-defaults.conf</path>. When you are
347 merging a Java package, and it detects one of the VM in that file is installed,
348 it will automatically use that VM, instead of the system-vm.
349 </p>
350
351 <p>
352 The merge time VM switching is also needed when, for example, your system-vm is
353 set a 1.4 VM and the package you are merging requires a 1.5 VM. While merging
354 it will use the preferred 1.5 VM, leaving your system-vm choice intact.
355 </p>
356
357 <p>
358 Of course, Gentoo is all about choice, so you can override these defaults in
359 <path>/etc/java-config-2/build/jdk.conf</path> and have complete control over
360 which VM will get used. Some examples:
361 </p>
362
363 <pre caption="Example /etc/java-config-2/build/jdk.conf">
364 <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>
365 *=sun-jdk
366 </pre>
367
368 <pre caption="Example /etc/java-config-2/build/jdk.conf">
369 <comment>(Always use sun-jdk-1.5 wherever possible, except for when a 1.4 or 1.3 VM is explicitly required)</comment>
370 *=sun-jdk-1.5
371 </pre>
372
373 <pre caption="Example /etc/java-config-2/build/jdk.conf">
374 <comment># For 1.3 I prefer sun-jdk 1.4 but when it is not available, use ibm-jdk-bin,
375 # For 1.4, use blackdown-jdk, and for 1.5, use sun-jdk </comment>
376 1.3=sun-jdk-1.4 ibm-jdk-bin
377 1.4=blackdown-jdk
378 1.5=sun-jdk
379 </pre>
380
381 <warn>
382 You do not have to edit this file. If you change these options to use a
383 unsupported VM, things could possibly break. Bugs reported with a unsupported
384 VM won't be prioritized as much as bugs present within supported VMs.
385 </warn>
386
387 </body>
388 </section>
389 </chapter>
390
391 <chapter>
392 <title>Compilers</title>
393 <section>
394 <body>
395
396 <p>
397 The standard Java compiler used for building is javac, which comes with each
398 JDK. In addition to configuring the VM used at build time, it is also possible
399 configure which compiler is used. Essentially, you define a list your
400 preference for which compiler to use in
401 <path>/etc/java-config-2/build/compilers.conf</path>.
402 </p>
403
404 <pre caption="/etc/java-config-2/build/compilers.conf">
405 # If the ebuild supports it
406 # it will check the COMPILERS var front to back and
407 # use the first compiler that is installed
408
409 COMPILERS="ecj-3.1 jikes javac"
410 </pre>
411
412 <p>
413 Some compilers don't support all possible -target and -source arguments.
414 Therefore, each compiler in the list is checked to see if it can support the
415 desired -source/-target. javac will work in all cases, so if no other suitable
416 compiler is found, it will be used instead.
417 </p>
418
419 <p>
420 More details about each compiler are provided below:
421 </p>
422
423 <table>
424 <tr>
425 <th>Name</th>
426 <th>Handle</th>
427 <th>Package</th>
428 <th>Description</th>
429 </tr>
430 <tr>
431 <ti>javac</ti>
432 <ti>javac</ti>
433 <ti>N/A</ti>
434 <ti>
435 This is the default compiler that will be used, and comes with each JDK.
436 </ti>
437 </tr>
438 <tr>
439 <ti>jikes</ti>
440 <ti>jikes</ti>
441 <ti>dev-java/jikes</ti>
442 <ti>
443 Jikes was originally developed by IBM. Anecdotally, it is generally quicker
444 than javac. Note however, that it is more pedantic, and will fail under a
445 few circumstances where javac has no issue. It also does not support Java
446 1.5 syntax yet.
447 </ti>
448 </tr>
449 <tr>
450 <ti>Eclipse Compiler for Java</ti>
451 <ti>ecj-3.1</ti>
452 <ti>=dev-java/eclipse-ecj-3.1*</ti>
453 <ti>
454 ECJ is the compiler used by the Eclipse software development kit. It is
455 very full featured, and is pretty fast. It does support Java 1.5 syntax.
456 </ti>
457 </tr>
458 </table>
459
460 </body>
461 </section>
462 </chapter>
463
464 <chapter>
465 <title>Setting a default CLASSPATH</title>
466 <section>
467 <body>
468
469 <warn>
470 The options explained in this section should be considered deprecated and will
471 most likely be removed in the future. We strongly recommend against using
472 these, because your Java projects or application should ideally manage their
473 own classpaths. If you choose to specify a default CLASSPATH, some applications
474 may behave unexpectedly, because classes they weren't expecting would be on the
475 classpath.
476 </warn>
477
478 <p>
479 <c>java-config</c> can also be used to set a system-wide default CLASSPATH, as
480 well a user-specific default CLASSPATH.
481 </p>
482
483 <p>
484 First, you will want to list available Java libraries installed on your system
485 that might want to be put in your CLASSPATH. Here is an example of output:
486 </p>
487
488 <pre caption="Listing classes">
489 # <i>java-config --list-available-packages</i>
490 [xerces-2] The next generation of high performance, fully compliant XML parsers in the Apache Xerces family (/usr/share/xerces-2/package.env)
491 [junit] Simple framework to write repeatable tests (/usr/share/junit/package.env)
492 [bsh] BeanShell: A small embeddable Java source interpreter (/usr/share/bsh/package.env)
493 [bcel] The Byte Code Engineering Library: analyze, create, manipulate Java class files (/usr/share/bcel/package.env)
494 [log4j] A low-overhead robust logging package for Java (/usr/share/log4j/package.env)
495 ...
496 </pre>
497
498 <p>
499 Again, the names in brackets (<e>[]</e>) are the IDs that you have to pass to
500 <c>java-config --set-system-classpath</c>. Here is an example:
501 </p>
502
503 <pre caption="Setting classpaths">
504 # <i>java-config --set-system-classpath log4j,xerces-2</i>
505 </pre>
506
507 <note>
508 The current directory (<path>.</path>) will not be part of the system
509 classpath, as that should be added in your system's login profile.
510 </note>
511
512 <p>
513 You will have to update your environment by logging out, then in again or
514 sourcing <path>/etc/profile</path>.
515 </p>
516
517 <p>
518 For users, <c>java-config --set-user-classpath</c> will create
519 <path>~/.gentoo/java-env-classpath</path>, which you should then source from
520 your shell's profile.
521 </p>
522
523 <pre caption="Sourcing user specific classpath">
524 <i>if [[ -f "${HOME}/.gentoo/java-env-classpath" ]]; then
525 source ${HOME}/.gentoo/java-env-classpath
526 fi</i>
527 </pre>
528
529 <p>
530 If you really want a system wide or user default classpath you can add
531 something like the following to your shell's profile. But we would advise
532 against it.
533 </p>
534
535 <pre caption="Setting classpath">
536 # <i>export CLASSPATH="${CLASSPATH}:$(java-config --classpath log4j,xerces-2)"</i>
537 </pre>
538
539 </body>
540 </section>
541 </chapter>
542
543 <chapter>
544 <title>USE flags for use with Java</title>
545 <section>
546 <title>Setting USE flags</title>
547 <body>
548
549 <p>
550 For more information regarding USE flags, refer to the <uri
551 link="/doc/en/handbook/handbook-x86.xml?part=2&amp;chap=2">USE flags</uri>
552 chapter from the Gentoo Handbook.
553 </p>
554
555 </body>
556 </section>
557 <section>
558 <title>The flags</title>
559 <body>
560
561 <ul>
562 <li>The <b>java</b> flag adds support for Java in a variety of programs</li>
563 <li>
564 The <b>nsplugin</b> flag adds support for Mozilla-like browsers (including
565 Firefox).You will need this for viewing Java applets in your Mozilla-like
566 browser.
567 </li>
568 <li>
569 The <b>doc</b> flag will typically install API documentation, as generated
570 by javadoc.
571 </li>
572 <li>
573 The <b>source</b> flag installs a zip of the source code of a package.
574 This is traditionally used for for IDEs to 'attach' source to the libraries
575 you are using.
576 </li>
577 <li>
578 For Java packages, the <b>doc</b> flag will build API documentation using
579 javadoc.
580 </li>
581 </ul>
582
583 </body>
584 </section>
585 </chapter>
586
587 <chapter>
588 <title>Additional resources</title>
589 <section>
590 <title>Off-line resources</title>
591 <body>
592
593 <ul>
594 <li>java-config man page</li>
595 <li><c>java-config --help</c></li>
596 </ul>
597
598 </body>
599 </section>
600 <section>
601 <title>Online resources</title>
602 <body>
603
604 <ul>
605 <li>
606 The <uri link="http://www.gentoo.org/proj/en/java/">Java Project
607 Page</uri>
608 </li>
609 <li>
610 The <uri
611 link="http://news.gmane.org/gmane.linux.gentoo.java">gentoo-java</uri>,
612 <uri
613 link="http://news.gmane.org/gmane.linux.gentoo.user">gentoo-user</uri>, and
614 <uri
615 link="http://news.gmane.org/gmane.linux.gentoo.devel">gentoo-dev</uri>
616 mailing list archives
617 </li>
618 <li>#gentoo and #gentoo-java on irc.freenode.net</li>
619 <li>
620 <uri
621 link="http://en.wikipedia.org/wiki/Java_programming_language">Wikipedia's
622 entry for Java</uri>
623 </li>
624 </ul>
625
626 </body>
627 </section>
628 </chapter>
629 </guide>

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