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Overhauled, updated java guide for bug 137760. thanks to nichoj for putting in all the time and energy on the update.

1 <?xml version="1.0" encoding="UTF-8"?>
2 <!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/java.xml,v 1.15 2005/03/23 13:40:23 swift 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="karltk@gentoo.org">Karl Trygve Kalleberg</mail>
10 </author>
11 <author title="Author">
12 <mail link="nichoj@gentoo.org">Joshua Nichols</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>0.4</version>
28 <date>2006-06-24</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>Installing a JRE/JDK</title>
61 <section>
62 <title>The choices</title>
63 <body>
64
65 <p>
66 Gentoo provides numerous JREs and JDKs. Among the current alternatives, we
67 have:
68 </p>
69
70 <table>
71 <tr>
72 <th>Vendor</th>
73 <th>JDK</th>
74 <th>JRE</th>
75 </tr>
76 <tr>
77 <ti>The Blackdown Java Kit</ti>
78 <ti>dev-java/backdown-jdk</ti>
79 <ti>dev-java/blackdown-jre</ti>
80 </tr>
81 <tr>
82 <ti>Sun's Java Kit</ti>
83 <ti>dev-java/sun-jdk</ti>
84 <ti>dev-java/sun-jre-bin</ti>
85 </tr>
86 <tr>
87 <ti>The IBM Java Kit</ti>
88 <ti>dev-java/ibm-jdk-bin</ti>
89 <ti>dev-java/ibm-jre-bin</ti>
90 </tr>
91 <tr>
92 <ti>The Compaq Java Kit for Alpha/Linux/GNU</ti>
93 <ti>dev-java/compaq-jdk</ti>
94 <ti>dev-java/compaq-jre</ti>
95 </tr>
96 <tr>
97 <ti>BEA WebLogic's J2SE Development Kit</ti>
98 <ti>dev-java/jrockit-jdk-bin</ti>
99 </tr>
100 </table>
101
102 <!--
103 TODO: list free implmentations?
104 note about not drop-in replacemenets
105 kaffe/sablevm/gcj/jamvm
106 -->
107
108 <p>
109 The default is Blackdown for both the JRE and the JDK, as it is freely ("free
110 as in beer") available without any registration fuss.
111 </p>
112
113 <p>
114 Both the Sun and the IBM are generally faster, but getting them is a bit more
115 hassle, as you are required to read and accept their license before downloading
116 (IBM additionally requires you to register).
117 </p>
118
119 <p>
120 Our ebuilds for the Sun and IBM JRE/JDKs will inform you how to download the
121 appropriate files.
122 </p>
123
124 </body>
125 </section>
126 <section>
127 <title>Installing a JRE/JDKs</title>
128 <body>
129
130 <p>
131 To install your profile's default JDK, you can run <c>emerge virtual/jdk</c>.
132 Or to install your profile's default JRE, you can <c>emerge virtual/jre</c>.
133 </p>
134
135 <note>
136 A JDK also includes a JRE, so if you install a JDK you shouldn't have to also
137 have to install a JRE.
138 </note>
139
140 </body>
141 </section>
142 <section>
143 <title>Installing the Sun/IBM JRE/JDKs</title>
144 <body>
145
146 <p>
147 If you run <c>emerge dev-java/sun-jdk</c> or <c>emerge
148 dev-java/ibm-jdk-bin</c>, you will be notified that you are required to
149 download the actual files yourself. This has to do with license restrictions
150 for the Sun JRE/JDK (online click-wrap license) and registration issues with
151 the IBM JRE/JDK.
152 </p>
153
154 <p>
155 You should download the indicated file(s) into
156 <path>/usr/portage/distfiles</path>. Once there, you can rerun the emerge
157 command, at which point the JRE/JDK will be begin to install.
158 </p>
159
160 </body>
161 </section>
162 </chapter>
163
164 <chapter>
165 <title>Configuring your JRE/JDK</title>
166 <section>
167 <title>Overview</title>
168 <body>
169
170 <p>
171 Gentoo has the ability to have multiple JDKs and JREs installed without causing
172 conflicts.
173 </p>
174
175 <p>
176 Using the <c>java-config</c> tool, you can set the system-wide default
177 (provided you have root access). Users can also use <c>java-config</c> to set
178 up their own personal default.
179 </p>
180
181 <note>
182 You can also use <e>eselect</e> to change the system and user vm. See
183 <c>eselect java help</c>.
184 </note>
185
186 </body>
187 </section>
188 <section>
189 <title>Setting a default JRE/JDK</title>
190 <body>
191
192 <p>
193 Running the command <c>java-config --list-available-vms</c> will give you a
194 list of all JREs and JDKs installed on your system. Here is an example of
195 output:
196 </p>
197
198 <pre caption="Listing available VMs">
199 # <i>java-config --list-available-vms</i>
200 1) Blackdown JDK 1.3.1 [blackdown-jdk-1.3] (/etc/env.d/java/20blackdown-jdk-1.3)
201 2) Blackdown JDK 1.4.2.02 [blackdown-jdk-1.4] (/etc/env.d/java/20blackdown-jdk-1.4)
202 3) Blackdown JRE 1.4.2.02 [blackdown-jre-1.4] (/etc/env.d/java/20blackdown-jre-1.4)
203 4) IBM JDK 1.4.2 [ibm-jdk-bin-1.4] (/etc/env.d/java/20ibm-jdk-bin-1.4)
204 5) IBM JRE 1.4.2 [ibm-jre-bin-1.4] (/etc/env.d/java/20ibm-jre-bin-1.4)
205 6) WebLogic JRockit 1.4.2.05 [jrockit-jdk-bin-1.4] (/etc/env.d/java/20jrockit-jdk-bin-1.4)
206 7) WebLogic JRockit 1.5.0.03 [jrockit-jdk-bin-1.5] (/etc/env.d/java/20jrockit-jdk-bin-1.5)
207 8) Sun JDK 1.3.1.13 [sun-jdk-1.3] (/etc/env.d/java/20sun-jdk-1.3)
208 9) Sun JDK 1.4.2.09 [sun-jdk-1.4] (/etc/env.d/java/20sun-jdk-1.4)
209 *) Sun JDK 1.5.0.04 [sun-jdk-1.5] (/etc/env.d/java/20sun-jdk-1.5)
210 11) Sun JRE 1.4.2.09 [sun-jre-bin-1.4] (/etc/env.d/java/20sun-jre-bin-1.4)
211 12) Sun JRE 1.5.0.04 [sun-jre-bin-1.5] (/etc/env.d/java/20sun-jre-bin-1.5)
212 </pre>
213
214 <p>
215 The <e>*</e> indicates this is the current active vm (system-vm or user-vm when
216 set). The name in the brackets (<e>[]</e>) is the handle or ID for that
217 particular VM. You use the handle or the number to <c>java-config
218 --set-system-vm</c>. Here is an example of how to set the system VM.
219 </p>
220
221 <pre caption="Setting the System VM">
222 <comment>(By handle (preferred))</comment>
223 # <i>java-config --set-system-vm blackdown-jdk-1.4</i>
224 <comment>(By number)</comment>
225 # <i>java-config --set-system-vm 2</i>
226 </pre>
227
228 <p>
229 As a regular user, you can use <c>java-config --set-user-vm</c>.
230 </p>
231
232 <note>
233 You no longer have to <c>source</c> the profile for updates to the user/system
234 VM take place.
235 </note>
236
237 </body>
238 </section>
239 <section id="preferred-vm">
240 <title>Preferred VM</title>
241 <body>
242
243 <p>
244 While merging Java packages, the VM can and will be switched as necessary.
245 </p>
246
247 <p>
248 Because of the wide variety of available VMs, we do not have the resources to
249 test and verify every package works on all of them. So to ensure that every
250 packages merges smoothly, we have defined a list of <e>default/supported
251 VMs</e> per arch. You can find them in
252 <path>/usr/share/java-config/config/jdk-defaults.conf</path>. When you are
253 merging a Java package, and it detects one of the VM in that file is installed,
254 it will automatically use that VM, instead of the system-vm.
255 </p>
256
257 <p>
258 The merge time VM switching is also needed when, for example, your system-vm is
259 set a 1.4 VM and the package you are merging requires a 1.5 VM. While merging
260 it will use the preferred 1.5 VM, leaving your system-vm choice intact.
261 </p>
262
263 <p>
264 Of course, Gentoo is all about choice, so you can override these defaults in
265 <path>/etc/java-config-2/build/jdk.conf</path> and have complete control over
266 which VM will get used. Some examples:
267 </p>
268
269 <pre caption="Example /etc/java-config-2/build/jdk.conf">
270 <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>
271 *=sun-jdk
272 </pre>
273
274 <pre caption="Example /etc/java-config-2/build/jdk.conf">
275 <comment>(Always use sun-jdk-1.5 wherever possible, except for when a 1.4 or 1.3 VM is explicitly required)</comment>
276 *=sun-jdk-1.5
277 </pre>
278
279 <pre caption="Example /etc/java-config-2/build/jdk.conf">
280 <comment># For 1.3 I prefer sun-jdk 1.4 but when it is not available, use ibm-jdk-bin,
281 # For 1.4, use blackdown-jdk, and for 1.5, use sun-jdk </comment>
282 1.3=sun-jdk-1.4 ibm-jdk-bin
283 1.4=blackdown-jdk
284 1.5=sun-jdk
285 </pre>
286
287 <warn>
288 You do not have to edit this file. If you change these options to use a
289 unsupported VM, things could possibly break. Bugs reported with a unsupported
290 VM will a lower priority if they aren't present with supported VMs.
291 </warn>
292
293 </body>
294 </section>
295 </chapter>
296
297 <chapter>
298 <title>Compilers</title>
299 <section>
300 <body>
301
302 <p>
303 The standard Java compiler used for building is javac, which comes with each
304 JDK. In addition to configuring the VM used at build time, it is also possible
305 configure which compiler is used. Essentially, you define a list your
306 preference for which compiler to use in
307 <path>/etc/java-config-2/build/compilers.conf</path>.
308 </p>
309
310 <pre caption="/etc/java-config-2/build/compilers.conf">
311 # If the ebuild supports it
312 # it will check the COMPILERS var front to back and
313 # use the first compiler that is installed
314
315 COMPILERS="ecj-3.1 jikes javac"
316 </pre>
317
318 <p>
319 Some compilers don't support all possible -target and -source arguments.
320 Therefore, each compiler in the list is checked to see if it can support the
321 desired -source/-target. javac will work in all cases, so if no other suitable
322 compiler is found, it will be used instead.
323 </p>
324
325 <p>
326 More details about each compiler are provided below:
327 </p>
328
329 <table>
330 <tr>
331 <th>Name</th>
332 <th>Handle</th>
333 <th>Package</th>
334 <th>Description</th>
335 </tr>
336 <tr>
337 <ti>javac</ti>
338 <ti>javac</ti>
339 <ti>N/A</ti>
340 <ti>
341 This is the default compiler that will be used, and comes with each JDK.
342 </ti>
343 </tr>
344 <tr>
345 <ti>jikes</ti>
346 <ti>jikes</ti>
347 <ti>dev-java/jikes</ti>
348 <ti>
349 Jikes was originally developed by IBM. Anecdotally, it is generally quicker
350 than javac. Note however, that it is more pedantic, and will fail under a
351 few circumstances where javac has no issue. It also does not support Java
352 1.5 syntax yet.
353 </ti>
354 </tr>
355 <tr>
356 <ti>Eclipse Compiler for Java</ti>
357 <ti>ecj-3.1</ti>
358 <ti>=dev-java/eclipse-ecj-3.1*</ti>
359 <ti>
360 ECJ is the compiler used by the Eclipse software development kit. It is
361 very full featured, and is pretty fast. It does support Java 1.5 syntax.
362 </ti>
363 </tr>
364 </table>
365
366 </body>
367 </section>
368 </chapter>
369
370 <chapter>
371 <title>Setting a default CLASSPATH</title>
372 <section>
373 <body>
374
375 <warn>
376 The options explained in this section should be considered deprecated and will
377 be most likely be removed in the future. We strongly recommend against using
378 these, because your Java projects or application should ideally manage their
379 own classpaths. If you choose to specify a default CLASSPATH, some applications
380 may behave unexpectedly, because classes they weren't expecting would be on the
381 classpath.
382 </warn>
383
384 <p>
385 <c>java-config</c> can also be used to set a system-wide default CLASSPATH, as
386 well a user-specific default CLASSPATH.
387 </p>
388
389 <p>
390 First, you will want to list available Java libraries installed on your system
391 that might want to be put in your CLASSPATH. Here is an example of output:
392 </p>
393
394 <pre caption="Listing classes">
395 # <i>java-config --list-available-packages</i>
396 [xerces-2] The next generation of high performance, fully compliant XML parsers in the Apache Xerces family (/usr/share/xerces-2/package.env)
397 [junit] Simple framework to write repeatable tests (/usr/share/junit/package.env)
398 [bsh] BeanShell: A small embeddable Java source interpreter (/usr/share/bsh/package.env)
399 [bcel] The Byte Code Engineering Library: analyze, create, manipulate Java class files (/usr/share/bcel/package.env)
400 [log4j] A low-overhead robust logging package for Java (/usr/share/log4j/package.env)
401 ...
402 </pre>
403
404 <p>
405 Again, the names in brackets (<e>[]</e>) are the IDs that you have to pass to
406 <c>java-config --set-system-classpath</c>. Here is an example:
407 </p>
408
409 <pre caption="Setting classpaths">
410 # <i>java-config --set-system-classpath log4j,xerces-2</i>
411 </pre>
412
413 <note>
414 The current directory (<path>.</path>) will not be part of the system
415 classpath, as that should be added in your system's login profile.
416 </note>
417
418 <p>
419 You will have to update your environment by relogging in or sourcing
420 <path>/etc/profile</path>.
421 </p>
422
423 <p>
424 For users, <c>java-config --set-user-classpath</c> will create
425 <path>~/.gentoo/java-env-classpath</path>, which you should then source from
426 your shell's profile.
427 </p>
428
429 <pre caption="Sourcing user specific classpath">
430 <i>if [[ -f "${HOME}/.gentoo/java-env-classpath" ]]; then
431 source ${HOME}/.gentoo/java-env-classpath
432 fi</i>
433 </pre>
434
435 <p>
436 If you really want a system wide or user default classpath you can add
437 something like like the following to your shell's profile. But we would advise
438 against it.
439 </p>
440
441 <pre caption="Setting classpath">
442 # <i>export CLASSPATH="${CLASSPATH}:$(java-config --classpath log4j,xerces-2)"</i>
443 </pre>
444
445 </body>
446 </section>
447 </chapter>
448
449 <chapter>
450 <title>USE flags for use with Java</title>
451 <section>
452 <title>Setting USE flags</title>
453 <body>
454
455 <p>
456 For more information regarding USE flags, refer to the <uri
457 link="/doc/en/handbook/handbook-x86.xml?part=2&amp;chap=2">USE flags</uri>
458 chapter from the Gentoo Handbook.
459 </p>
460
461 </body>
462 </section>
463 <section>
464 <title>The flags</title>
465 <body>
466
467 <ul>
468 <li>The <b>java</b> flag adds support for Java in a variety of programs</li>
469 <li>
470 The <b>nsplugin</b> flag adds support for Mozilla-like browsers (including
471 Firefox).You will need this for viewing Java applets in your Mozilla-like
472 browser.
473 </li>
474 <li>
475 The <b>doc</b> flag will typically install API documentation, as generated
476 by javadoc.
477 </li>
478 <li>
479 The <b>source</b> flag will install a zip of the package's source code.
480 This is typically used to provide your IDE with the source code for the
481 package.
482 </li>
483 </ul>
484
485 </body>
486 </section>
487 </chapter>
488
489 <chapter>
490 <title>Additional resources</title>
491 <section>
492 <title>Off-line resources</title>
493 <body>
494
495 <ul>
496 <li>java-config man page</li>
497 <li><c>java-config --help</c></li>
498 </ul>
499
500 </body>
501 </section>
502 <section>
503 <title>Online resources</title>
504 <body>
505
506 <ul>
507 <li>
508 The <uri link="http://www.gentoo.org/proj/en/java/">Java Project
509 Page</uri>
510 </li>
511 <li>
512 The <uri
513 link="http://news.gmane.org/gmane.linux.gentoo.java">gentoo-java</uri>,
514 <uri
515 link="http://news.gmane.org/gmane.linux.gentoo.user">gentoo-user</uri>, and
516 <uri
517 link="http://news.gmane.org/gmane.linux.gentoo.devel">gentoo-dev</uri>
518 mailing list archives
519 </li>
520 <li>#gentoo and #gentoo-java on irc.freenode.net</li>
521 <li>
522 <uri
523 link="http://en.wikipedia.org/wiki/Java_programming_language">Wikipedia's
524 entry for Java</uri>
525 </li>
526 </ul>
527
528 </body>
529 </section>
530 </chapter>
531 </guide>

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