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1 <?xml version="1.0" encoding="UTF-8"?>
2 <!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/java.xml,v 1.13 2005/02/07 19:27:44 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 and Editor">
9 <mail link="karltk@gentoo.org">Karl Trygve Kalleberg</mail>
10 </author>
11 <author title="Editor">
12 <mail link="swift@gentoo.org">Sven Vermeulen</mail>
13 </author>
14 <author title="Editor">
15 <mail link="marcelogoes@gmail.com">Marcelo Góes</mail>
16 </author>
17
18 <abstract>
19 This guide will introduce users and developers to Java and explain how to use
20 Java with Gentoo Linux.
21 </abstract>
22
23 <license/>
24
25 <version>0.1.6</version>
26 <date>2005-03-06</date>
27
28 <chapter>
29 <title>What is Java?</title>
30 <section>
31 <title>Overview</title>
32 <body>
33
34 <p>
35 Java is a programming language developed by engineers of Sun Microsystems.
36 The language is object-oriented and designed to run on multiple platforms
37 without the need of recompiling code for each platform. Although Java can
38 be compiled as a native program, much of Java's popularity can be attributed
39 to its portability, along with other features such as garbage collection.
40 The ability to compile once and run in various platforms is achieved through
41 the use of just-in-time compilers (JIT), which compile Java bytecodes into
42 native code when a given program is run.
43 </p>
44
45 <p>
46 In order to run Java bytecodes, one needs to have a JRE (Java Runtime Environment)
47 installed. A JRE provides core libraries, a platform dependent Java Virtual Machine,
48 plug-ins for browsers, among other things. A JDK (Java Development Kit) adds
49 programming tools, such as a bytecode compiler and a debugger.
50 </p>
51
52 </body>
53 </section>
54 </chapter>
55
56 <chapter>
57 <title>Installing a JRE/JDK</title>
58 <section>
59 <title>The choices</title>
60 <body>
61
62 <p>
63 Gentoo provides numerous JREs and JDKs. Among the current alternatives, we have:
64 </p>
65
66 <ul>
67 <li>blackdown-jre and blackdown-jdk, the Blackdown Java Kit</li>
68 <li>sun-jre-bin and sun-jdk, Sun's Java Kit </li>
69 <li>ibm-jre-bin and ibm-jdk-bin, the IBM Java Kit</li>
70 <li>compaq-jre and compaq-jdk, the Compaq Java Kit for Alpha/Linux/GNU</li>
71 <li>jrockit-jdk-bin, BEA WebLogic's J2SE Development Kit</li>
72 </ul>
73
74 <p>
75 The default is the Blackdown JRE/JDK
76 pair, as it is freely ("free as in beer") available without any registration
77 fuss.
78 </p>
79
80 <p>
81 Both the Sun JRE/JDK and the IBM JRE/JDK are generally faster, but getting them
82 is a bit more work, as you are required to read and accept their license before
83 downloading (IBM additionally requires you to register).
84 </p>
85
86 <p>
87 Our ebuilds for the Sun and IBM JRE/JDKs will notify you of where to go to
88 download them.
89 </p>
90
91 </body>
92 </section>
93
94 <section>
95 <title>Installing the Sun/IBM JRE/JDKs</title>
96 <body>
97
98 <p>
99 If you run <c>emerge =sun-jdk-1.4.2.06</c> or <c>=ibm-jdk-bin-1.4.2</c>, you will
100 be notified that you are required to download the actual tarballs yourself. This
101 has to do with license restrictions for the Sun JRE/JDK (online click-wrap
102 license) and registration issues with the IBM JRE/JDK.
103 </p>
104
105 <note>
106 ibm-jdk-bin is currently masked, you may have to unmask it to use it.
107 </note>
108
109 <p>
110 You should download the indicated file(s) into
111 <path>/usr/portage/distfiles</path>. Once that is done, you can rerun the emerge
112 command, then the JRE/JDK will be installed properly into <path>/opt</path>.
113 </p>
114
115 </body>
116 </section>
117 </chapter>
118
119 <chapter>
120 <title>Configuring your JRE/JDK</title>
121 <section>
122 <title>Overview</title>
123 <body>
124
125 <p>
126 Gentoo has the ability to have multiple JDKs and JREs installed without them
127 conflicting.
128 </p>
129
130 <p>
131 Using the <c>java-config</c> tool, you can set the system-wide default if you
132 have root access. Users can also use <c>java-config</c> to set up their own
133 personal default, that is different from the system-wide default.
134 </p>
135
136 </body>
137 </section>
138
139 <section>
140 <title>Setting a default JRE/JDK</title>
141 <body>
142
143 <p>
144 Running the command <c>java-config --list-available-vms</c> will give you a list
145 of all available JREs and JDKs on your system. Here is an example of output:
146 </p>
147
148 <pre caption="Listing available VMs">
149 # <i>java-config --list-available-vms</i>
150 [blackdown-jdk-1.3.1] Blackdown JDK 1.3.1 (/etc/env.d/java/20blackdown-jdk-1.3.1)
151 [blackdown-jre-1.3.1] Blackdown JRE 1.3.1 (/etc/env.d/java/20blackdown-jre-1.3.1)
152 [ibm-jdk-1.3.0] IBM JDK 1.3.0 (/etc/env.d/java/20ibm-jdk-1.3.0)
153 [ibm-jdk-1.3.1] IBM JDK 1.3.1 (/etc/env.d/java/20ibm-jdk-1.3.1)
154 [ibm-jre-1.3.1] IBM JRE 1.3.1 (/etc/env.d/java/20ibm-jre-1.3.1)
155 [sun-jdk-1.4.0] Sun JDK 1.4.0 (/etc/env.d/java/20sun-jdk-1.4.0)
156 </pre>
157
158 <p>
159 The name in the brackets <path>"[]"</path> is the handle or ID for that
160 particular VM. You use pass that ID to <c>java-config --set-system-vm</c>. Here is
161 an example of how to set the system VM.
162 </p>
163
164 <pre caption="Setting the System VM">
165 # <i>java-config --set-system-vm=ibm-jdk-1.3.1</i>
166 Now using IBM JDK 1.3.1 (/etc/env.d/java/20ibm-jdk-1.3.1)
167 </pre>
168
169 <note>
170 You will have to be root to run --set-system-vm.
171 </note>
172
173 <p>
174 Once you have issued <c>java-config --set-system-vm</c> with a particular VM ID,
175 you will need to regenerate your /etc/profile.env. You can do it like this:
176 </p>
177
178 <pre caption="Regenerating /etc/profile.env" >
179 # <i>env-update</i>
180 </pre>
181
182 <p>
183 After this, you will either want to relogin, or resource
184 <path>/etc/profile</path> into your environment.
185 </p>
186
187 <p>
188 As a regular user, you can use <c>java-config --set-user-vm</c>, which will
189 create <path>~/.gentoo/java-env</path> with all required env vars. You would
190 normally source this from your shell's startup script
191 (generally <path>~/.bashrc</path>).
192 </p>
193
194 </body>
195 </section>
196
197 <section>
198 <title>Setting a default CLASSPATH</title>
199 <body>
200
201 <p>
202 <c>java-config</c> can also be used to set a system-wide default CLASSPATH, and
203 of course a user-specific default CLASSPATH.
204 </p>
205
206 <p>
207 First you want to list available java libraries that might be interesting to put
208 in your CLASSPATH. Here is an example of output:
209 </p>
210
211 <pre caption="Listing classes">
212 # <i>java-config --list-available-packages</i>
213 [bsh] BeanShell is a small, free, embeddable, Java
214 source interpreter with object scripting language
215 features. (/usr/share/bsh/package.env)
216 [oro] A set of text-processing Java classes that
217 provide Perl5 compatible regular expressions, AWK-like
218 regular expressions, glob expressions, and utility
219 classes for performing substitutions, splits, filtering
220 filenames, etc. (/usr/share/oro/package.env)
221 [bcel] The Byte Code Engineering Library: analyze, create,
222 manipulate Java class files (/usr/share/bcel/package.env)
223 [jsch] JSch is a pure Java implementation of SSH2.
224 (/usr/share/jsch/package.env)
225 ...
226 </pre>
227
228 <p>
229 Again, the name in brackets <path>"[]"</path> are the IDs that you have to pass
230 to <c>java-config --set-system-classpath</c>. Here is an example:
231 </p>
232
233 <pre caption="Setting classpaths">
234 # <i>java-config --set-system-classpath=log4j,java-gtk,java-gnome</i>
235 </pre>
236
237 <note>
238 The current directory (.) will not be part of the system classpath, as that
239 should be added in root's login profile.
240 </note>
241
242 <p>
243 Again, you will want to run <c>env-update</c> to update your system's
244 environment, and you might also want to relogin or resource the
245 <path>/etc/profile</path>.
246 </p>
247
248 <p>
249 For users, <c>java-config --set-user-classpath</c> will create
250 <path>~/.gentoo/java-env-classpath</path>, which is automatically included
251 by <path>~/.gentoo/java-env</path>.
252 </p>
253
254 </body>
255 </section>
256 </chapter>
257
258 <chapter>
259 <title>USE flags for use with Java</title>
260 <section>
261 <title>Setting USE flags</title>
262 <body>
263
264 <p>
265 For more information regarding USE flags, refer to the
266 <uri link="/doc/en/handbook/handbook-x86.xml?part=2&amp;chap=2">USE flags</uri>
267 chapter from the Gentoo Handbook.
268 </p>
269
270 </body>
271 </section>
272 <section>
273 <title>The flags</title>
274 <body>
275
276 <ul>
277 <li>The <b>java</b> flag adds support for Java in a variety of programs.</li>
278 <li>The <b>mozilla</b> flag adds support for Mozilla-like browsers (including Firefox)
279 if you are using blackdown's Java kit. You will need this for viewing Java applets
280 in your Mozilla-like browser.</li>
281 </ul>
282
283 </body>
284 </section>
285 </chapter>
286
287 <chapter>
288 <title>Additional resources</title>
289 <section>
290 <title>Off-line resources</title>
291 <body>
292
293 <ul>
294 <li>java-config man page</li>
295 <li><c>java-config --help</c></li>
296 <li>The <path>/usr/bin/java-config</path> script itself</li>
297 </ul>
298
299 </body>
300 </section>
301
302 <section>
303 <title>Online resources</title>
304 <body>
305 <ul>
306 <li>The <uri link="http://news.gmane.org/gmane.linux.gentoo.devel"
307 >gentoo-dev</uri>, <uri link="http://news.gmane.org/gmane.linux.gentoo.user"
308 >gentoo-user </uri> mailing list archives</li>
309 <li>#gentoo and #gentoo-java on irc.freenode.net</li>
310 <li><uri link="http://en.wikipedia.org/wiki/Java_programming_language">Wikipedia's entry for Java</uri></li>
311 </ul>
312
313 </body>
314 </section>
315 </chapter>
316 </guide>

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