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1 <?xml version="1.0" encoding="UTF-8"?>
2 <!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/java.xml,v 1.28 2006/08/08 09:51:12 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>0.7</version>
28 <date>2006-08-08</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 dev-java/sun-jce-bin
92 # JDKs
93 =dev-java/sun-jdk-1.4*
94 =dev-java/sun-jdk-1.5*
95 =dev-java/ibm-jdk-bin-1.4*
96 =dev-java/ibm-jdk-bin-1.5*
97 =dev-java/jrockit-jdk-bin-1.4*
98 =dev-java/jrockit-jdk-bin-1.5*
99 =dev-java/blackdown-jdk-1.4*
100 dev-java/kaffe
101 # JREs
102 =dev-java/sun-jre-bin-1.4*
103 =dev-java/sun-jre-bin-1.5*
104 =dev-java/ibm-jre-bin-1.4*
105 =dev-java/blackdown-jre-1.4*
106 # Virtuals
107 virtual/jdk
108 virtual/jre
109 # Compilers
110 dev-java/eclipse-ecj
111 dev-java/jikes
112 # Documentation
113 dev-java/java-sdk-docs
114 # Misc packages that have been updated to generation-2,
115 # where the generation-1 won't build and/or run properly
116 dev-java/lucene
117 # These have optional Java support, but need ~arch to function properly
118 # with generation-2
119 dev-util/subversion
120 sys-libs/db
121 </pre>
122
123 <impo>
124 It is crucial that you keyword ALL packages related to the new Java system,
125 otherwise you will have problems in the later steps of this guide.
126 </impo>
127
128 <impo>
129 It can't be emphasized enough that you have to have ALL the packages related
130 to the new Java system keyworded for it to function properly.
131 </impo>
132
133 </body>
134 </section>
135 <section>
136 <title>Existing installs</title>
137 <body>
138
139 <p>
140 For existing installs, regardless of if you have installed anything Java
141 before, make sure you have followed the <uri
142 link="/proj/en/java/java-upgrade.xml">Java Upgrade Guide</uri>.
143 </p>
144
145 </body>
146 </section>
147 <section>
148 <title>New installs</title>
149 <body>
150
151 <p>
152 New installs should require no further preparation.
153 </p>
154
155 </body>
156 </section>
157 </chapter>
158
159 <chapter>
160 <title>Installing a Virtual Machine</title>
161 <section>
162 <title>The choices</title>
163 <body>
164
165 <p>
166 Gentoo provides numerous Runtime Environments (JREs) and Development Kits
167 (JDKs). Among the current choices, we have:
168 </p>
169
170 <table>
171 <tr>
172 <th>Vendor</th>
173 <th>JDK</th>
174 <th>JRE</th>
175 </tr>
176 <tr>
177 <ti>The Blackdown Java Kit</ti>
178 <ti>dev-java/blackdown-jdk</ti>
179 <ti>dev-java/blackdown-jre</ti>
180 </tr>
181 <tr>
182 <ti>Sun's Java Kit</ti>
183 <ti>dev-java/sun-jdk</ti>
184 <ti>dev-java/sun-jre-bin</ti>
185 </tr>
186 <tr>
187 <ti>The IBM Java Kit</ti>
188 <ti>dev-java/ibm-jdk-bin</ti>
189 <ti>dev-java/ibm-jre-bin</ti>
190 </tr>
191 <tr>
192 <ti>The Compaq Java Kit for Alpha/Linux/GNU</ti>
193 <ti>dev-java/compaq-jdk</ti>
194 <ti>dev-java/compaq-jre</ti>
195 </tr>
196 <tr>
197 <ti>BEA WebLogic's J2SE Development Kit</ti>
198 <ti>dev-java/jrockit-jdk-bin</ti>
199 </tr>
200 </table>
201
202 <!--
203 TODO: list free implementations?
204 note about not drop-in replacements
205 kaffe/sablevm/gcj/jamvm
206 -->
207
208 <p>
209 The default is Blackdown for both the JRE and the JDK, as it is freely ("free
210 as in beer") available without any registration fuss.
211 </p>
212
213 <p>
214 The default for Java 1.4 is the Blackdown JRE/JDK pair, as it is freely
215 ("free as in beer") available without any registration fuss.
216 </p>
217
218 <p>
219 JREs and JDKs from Sun, IBM, and BEA are generally faster, but getting them
220 is a bit more work, as you are required to read and accept their license before
221 downloading (IBM additionally requires you to register).
222 </p>
223
224 </body>
225 </section>
226 <section>
227 <title>Installing a JRE/JDKs</title>
228 <body>
229
230 <p>
231 To install your profile's default JDK, you can run <c>emerge virtual/jdk</c>.
232 Or to install your profile's default JRE, you can <c>emerge virtual/jre</c>.
233 </p>
234
235 <p>
236 In recent events, Sun has relicensed their JDK and JRE under a more Linux
237 distro friendly license. As a result, Sun releases Java 1.5 and onwards are
238 freely downloadable, without any further hassle.
239 </p>
240
241 <note>
242 A JDK also includes a JRE, so if you install a JDK you shouldn't have to also
243 have to install a JRE.
244 </note>
245
246 </body>
247 </section>
248 <section>
249 <title>Installing fetch-restricted virtual machines</title>
250 <body>
251
252 <p>
253 As already mentioned, some of the JDKs and JREs require you to jump through a
254 few hoops before installing. Simply emerge the packages as you normally would.
255 The ebuilds will then instruct you where to go and what to download.
256 </p>
257
258 <p>
259 You should download the indicated file(s) into
260 <path>/usr/portage/distfiles</path>. Once there, you can rerun the emerge
261 command, at which point the JRE/JDK will be begin to install.
262 </p>
263
264 </body>
265 </section>
266 </chapter>
267
268 <chapter>
269 <title>Configuring your virtual machine</title>
270 <section>
271 <title>Overview</title>
272 <body>
273
274 <p>
275 Gentoo has the ability to have multiple JDKs and JREs installed without causing
276 conflicts.
277 </p>
278
279 <p>
280 Using the <c>java-config</c> tool, you can set the system-wide default
281 (provided you have root access). Users can also use <c>java-config</c> to set
282 up their own personal default.
283 </p>
284
285 <note>
286 You can also use <e>eselect</e> to change the system and user vm. See
287 <c>eselect java-vm help</c>.
288 </note>
289
290 </body>
291 </section>
292 <section>
293 <title>Setting a default virtual machine</title>
294 <body>
295
296 <p>
297 Running the command <c>java-config --list-available-vms</c> will give you a
298 list of all JREs and JDKs installed on your system. Here is an example of
299 output:
300 </p>
301
302 <pre caption="Listing available VMs">
303 # <i>java-config --list-available-vms</i>
304 1) Blackdown JDK 1.3.1 [blackdown-jdk-1.3] (/etc/env.d/java/20blackdown-jdk-1.3)
305 2) Blackdown JDK 1.4.2.02 [blackdown-jdk-1.4] (/etc/env.d/java/20blackdown-jdk-1.4)
306 3) Blackdown JRE 1.4.2.02 [blackdown-jre-1.4] (/etc/env.d/java/20blackdown-jre-1.4)
307 4) IBM JDK 1.4.2 [ibm-jdk-bin-1.4] (/etc/env.d/java/20ibm-jdk-bin-1.4)
308 5) IBM JRE 1.4.2 [ibm-jre-bin-1.4] (/etc/env.d/java/20ibm-jre-bin-1.4)
309 6) WebLogic JRockit 1.4.2.05 [jrockit-jdk-bin-1.4] (/etc/env.d/java/20jrockit-jdk-bin-1.4)
310 7) WebLogic JRockit 1.5.0.03 [jrockit-jdk-bin-1.5] (/etc/env.d/java/20jrockit-jdk-bin-1.5)
311 8) Sun JDK 1.3.1.13 [sun-jdk-1.3] (/etc/env.d/java/20sun-jdk-1.3)
312 9) Sun JDK 1.4.2.09 [sun-jdk-1.4] (/etc/env.d/java/20sun-jdk-1.4)
313 *) Sun JDK 1.5.0.04 [sun-jdk-1.5] (/etc/env.d/java/20sun-jdk-1.5)
314 11) Sun JRE 1.4.2.09 [sun-jre-bin-1.4] (/etc/env.d/java/20sun-jre-bin-1.4)
315 12) Sun JRE 1.5.0.04 [sun-jre-bin-1.5] (/etc/env.d/java/20sun-jre-bin-1.5)
316 </pre>
317
318 <p>
319 The <e>*</e> indicates this is the current active vm (system-vm or user-vm when
320 set). The name in the brackets (<e>[]</e>) is the handle or ID for that
321 particular VM. You use the handle or the number to <c>java-config
322 --set-system-vm</c>. Here is an example of how to set the system VM.
323 </p>
324
325 <pre caption="Setting the System VM">
326 <comment>(By handle (preferred))</comment>
327 # <i>java-config --set-system-vm blackdown-jdk-1.4</i>
328 <comment>(By number)</comment>
329 # <i>java-config --set-system-vm 2</i>
330 </pre>
331
332 <p>
333 As a regular user, you can use <c>java-config --set-user-vm</c>.
334 </p>
335
336 <note>
337 You no longer have to <c>source</c> the profile for updates to the user/system
338 VM take place.
339 </note>
340
341 </body>
342 </section>
343 <section id="preferred-vm">
344 <title>Preferred VM</title>
345 <body>
346
347 <p>
348 While merging Java packages, the VM can and will be switched as necessary.
349 </p>
350
351 <p>
352 Because of the wide variety of available VMs, we do not have the resources to
353 test and verify every package works on all of them. So to ensure that every
354 packages merges smoothly, we have defined a list of <e>default/supported
355 VMs</e> per arch. You can find them in
356 <path>/usr/share/java-config/config/jdk-defaults.conf</path>. When you are
357 merging a Java package, and it detects one of the VM in that file is installed,
358 it will automatically use that VM, instead of the system-vm.
359 </p>
360
361 <p>
362 The merge time VM switching is also needed when, for example, your system-vm is
363 set a 1.4 VM and the package you are merging requires a 1.5 VM. While merging
364 it will use the preferred 1.5 VM, leaving your system-vm choice intact.
365 </p>
366
367 <p>
368 Of course, Gentoo is all about choice, so you can override these defaults in
369 <path>/etc/java-config-2/build/jdk.conf</path> and have complete control over
370 which VM will get used. Some examples:
371 </p>
372
373 <pre caption="Example /etc/java-config-2/build/jdk.conf">
374 <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>
375 *=sun-jdk
376 </pre>
377
378 <pre caption="Example /etc/java-config-2/build/jdk.conf">
379 <comment>(Always use sun-jdk-1.5 wherever possible, except for when a 1.4 or 1.3 VM is explicitly required)</comment>
380 *=sun-jdk-1.5
381 </pre>
382
383 <pre caption="Example /etc/java-config-2/build/jdk.conf">
384 <comment># For 1.3 I prefer sun-jdk 1.4 but when it is not available, use ibm-jdk-bin,
385 # For 1.4, use blackdown-jdk, and for 1.5, use sun-jdk </comment>
386 1.3=sun-jdk-1.4 ibm-jdk-bin
387 1.4=blackdown-jdk
388 1.5=sun-jdk
389 </pre>
390
391 <warn>
392 You do not have to edit this file. If you change these options to use a
393 unsupported VM, things could possibly break. Bugs reported with a unsupported
394 VM won't be prioritized as much as bugs present within supported VMs.
395 </warn>
396
397 </body>
398 </section>
399 </chapter>
400
401 <chapter>
402 <title>Compilers</title>
403 <section>
404 <body>
405
406 <p>
407 The standard Java compiler used for building is javac, which comes with each
408 JDK. In addition to configuring the VM used at build time, it is also possible
409 configure which compiler is used. Essentially, you define a list your
410 preference for which compiler to use in
411 <path>/etc/java-config-2/build/compilers.conf</path>.
412 </p>
413
414 <pre caption="/etc/java-config-2/build/compilers.conf">
415 # If the ebuild supports it
416 # it will check the COMPILERS var front to back and
417 # use the first compiler that is installed
418
419 COMPILERS="ecj-3.1 jikes javac"
420 </pre>
421
422 <p>
423 Some compilers don't support all possible -target and -source arguments.
424 Therefore, each compiler in the list is checked to see if it can support the
425 desired -source/-target. javac will work in all cases, so if no other suitable
426 compiler is found, it will be used instead.
427 </p>
428
429 <p>
430 More details about each compiler are provided below:
431 </p>
432
433 <table>
434 <tr>
435 <th>Name</th>
436 <th>Handle</th>
437 <th>Package</th>
438 <th>Description</th>
439 </tr>
440 <tr>
441 <ti>javac</ti>
442 <ti>javac</ti>
443 <ti>N/A</ti>
444 <ti>
445 This is the default compiler that will be used, and comes with each JDK.
446 </ti>
447 </tr>
448 <tr>
449 <ti>jikes</ti>
450 <ti>jikes</ti>
451 <ti>dev-java/jikes</ti>
452 <ti>
453 Jikes was originally developed by IBM. Anecdotally, it is generally quicker
454 than javac. Note however, that it is more pedantic, and will fail under a
455 few circumstances where javac has no issue. It also does not support Java
456 1.5 syntax yet.
457 </ti>
458 </tr>
459 <tr>
460 <ti>Eclipse Compiler for Java</ti>
461 <ti>ecj-3.1</ti>
462 <ti>=dev-java/eclipse-ecj-3.1*</ti>
463 <ti>
464 ECJ is the compiler used by the Eclipse software development kit. It is
465 very full featured, and is pretty fast. It does support Java 1.5 syntax.
466 </ti>
467 </tr>
468 </table>
469
470 </body>
471 </section>
472 </chapter>
473
474 <chapter>
475 <title>Setting a default CLASSPATH</title>
476 <section>
477 <body>
478
479 <warn>
480 The options explained in this section should be considered deprecated and will
481 most likely be removed in the future. We strongly recommend against using
482 these, because your Java projects or application should ideally manage their
483 own classpaths. If you choose to specify a default CLASSPATH, some applications
484 may behave unexpectedly, because classes they weren't expecting would be on the
485 classpath.
486 </warn>
487
488 <p>
489 <c>java-config</c> can also be used to set a system-wide default CLASSPATH, as
490 well a user-specific default CLASSPATH.
491 </p>
492
493 <p>
494 First, you will want to list available Java libraries installed on your system
495 that might want to be put in your CLASSPATH. Here is an example of output:
496 </p>
497
498 <pre caption="Listing classes">
499 # <i>java-config --list-available-packages</i>
500 [xerces-2] The next generation of high performance, fully compliant XML parsers in the Apache Xerces family (/usr/share/xerces-2/package.env)
501 [junit] Simple framework to write repeatable tests (/usr/share/junit/package.env)
502 [bsh] BeanShell: A small embeddable Java source interpreter (/usr/share/bsh/package.env)
503 [bcel] The Byte Code Engineering Library: analyze, create, manipulate Java class files (/usr/share/bcel/package.env)
504 [log4j] A low-overhead robust logging package for Java (/usr/share/log4j/package.env)
505 ...
506 </pre>
507
508 <p>
509 Again, the names in brackets (<e>[]</e>) are the IDs that you have to pass to
510 <c>java-config --set-system-classpath</c>. Here is an example:
511 </p>
512
513 <pre caption="Setting classpaths">
514 # <i>java-config --set-system-classpath log4j,xerces-2</i>
515 </pre>
516
517 <note>
518 The current directory (<path>.</path>) will not be part of the system
519 classpath, as that should be added in your system's login profile.
520 </note>
521
522 <p>
523 You will have to update your environment by logging out, then in again or
524 sourcing <path>/etc/profile</path>.
525 </p>
526
527 <p>
528 For users, <c>java-config --set-user-classpath</c> will create
529 <path>~/.gentoo/java-env-classpath</path>, which you should then source from
530 your shell's profile.
531 </p>
532
533 <pre caption="Sourcing user specific classpath">
534 <i>if [[ -f "${HOME}/.gentoo/java-env-classpath" ]]; then
535 source ${HOME}/.gentoo/java-env-classpath
536 fi</i>
537 </pre>
538
539 <p>
540 If you really want a system wide or user default classpath you can add
541 something like the following to your shell's profile. But we would advise
542 against it.
543 </p>
544
545 <pre caption="Setting classpath">
546 # <i>export CLASSPATH="${CLASSPATH}:$(java-config --classpath log4j,xerces-2)"</i>
547 </pre>
548
549 </body>
550 </section>
551 </chapter>
552
553 <chapter>
554 <title>USE flags for use with Java</title>
555 <section>
556 <title>Setting USE flags</title>
557 <body>
558
559 <p>
560 For more information regarding USE flags, refer to the <uri
561 link="/doc/en/handbook/handbook-x86.xml?part=2&amp;chap=2">USE flags</uri>
562 chapter from the Gentoo Handbook.
563 </p>
564
565 </body>
566 </section>
567 <section>
568 <title>The flags</title>
569 <body>
570
571 <ul>
572 <li>The <b>java</b> flag adds support for Java in a variety of programs</li>
573 <li>
574 The <b>nsplugin</b> flag adds support for Mozilla-like browsers (including
575 Firefox).You will need this for viewing Java applets in your Mozilla-like
576 browser.
577 </li>
578 <li>
579 The <b>doc</b> flag will typically install API documentation, as generated
580 by javadoc.
581 </li>
582 <li>
583 The <b>source</b> flag will install a zip of the package's source code.
584 This is typically used to provide your IDE with the source code for the
585 package.
586 </li>
587 <li>
588 The <b>source</b> flag installs a zip of the source code of a package.
589 This is traditionally used for for IDEs to 'attach' source to the libraries
590 you are using.
591 </li>
592 <li>
593 For Java packages, the <b>doc</b> flag will build API documentation using
594 javadoc.
595 </li>
596 </ul>
597
598 </body>
599 </section>
600 </chapter>
601
602 <chapter>
603 <title>Additional resources</title>
604 <section>
605 <title>Off-line resources</title>
606 <body>
607
608 <ul>
609 <li>java-config man page</li>
610 <li><c>java-config --help</c></li>
611 </ul>
612
613 </body>
614 </section>
615 <section>
616 <title>Online resources</title>
617 <body>
618
619 <ul>
620 <li>
621 The <uri link="http://www.gentoo.org/proj/en/java/">Java Project
622 Page</uri>
623 </li>
624 <li>
625 The <uri
626 link="http://news.gmane.org/gmane.linux.gentoo.java">gentoo-java</uri>,
627 <uri
628 link="http://news.gmane.org/gmane.linux.gentoo.user">gentoo-user</uri>, and
629 <uri
630 link="http://news.gmane.org/gmane.linux.gentoo.devel">gentoo-dev</uri>
631 mailing list archives
632 </li>
633 <li>#gentoo and #gentoo-java on irc.freenode.net</li>
634 <li>
635 <uri
636 link="http://en.wikipedia.org/wiki/Java_programming_language">Wikipedia's
637 entry for Java</uri>
638 </li>
639 </ul>
640
641 </body>
642 </section>
643 </chapter>
644 </guide>

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