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1 <?xml version="1.0" encoding="UTF-8"?>
2 <!-- $Header: /home/cvsroot/gentoo/xml/htdocs/doc/en/java.xml,v 1.12 2003/11/22 10:01:56 neysx 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>0.1.5</version>
26 <date>2005-02-07</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 (beer) available without any registration fuss.
77 </p>
78
79 <p>
80 Both the Sun JRE/JDK and the IBM JRE/JDK are generally faster, but getting them
81 is a bit more work, as you are required to read and accept their license before
82 downloading (IBM additionally requires you to register).
83 </p>
84
85 <p>
86 Our ebuilds for the Sun and IBM JRE/JDKs will notify you of where to go to
87 download them.
88 </p>
89
90 </body>
91 </section>
92
93 <section>
94 <title>Installing the Sun/IBM JRE/JDKs</title>
95 <body>
96
97 <p>
98 If you run <c>emerge =sun-jdk-1.4.2.06</c> or <c>=ibm-jdk-bin-1.4.2</c>, you will
99 be notified that you are required to download the actual tarballs yourself. This
100 has to do with license restrictions for the Sun JRE/JDK (online click-wrap
101 license) and registration issues with the IBM JRE/JDK.
102 </p>
103
104 <note>
105 ibm-jdk-bin is currently masked, you may have to unmask it to use it.
106 </note>
107
108 <p>
109 You should download the indicated file(s) into
110 <path>/usr/portage/distfiles</path>. Once that is done, you can rerun the emerge
111 command, then the JRE/JDK will be installed properly into <path>/opt</path>.
112 </p>
113
114 </body>
115 </section>
116 </chapter>
117
118 <chapter>
119 <title>Configuring your JRE/JDK</title>
120 <section>
121 <title>Overview</title>
122 <body>
123
124 <p>
125 Gentoo has the ability to have multiple JDKs and JREs installed without them
126 conflicting.
127 </p>
128
129 <p>
130 Using the <c>java-config</c> tool, you can set the system-wide default if you
131 have root access. Users can also use <c>java-config</c> to set up their own
132 personal default, that is different from the system-wide default.
133 </p>
134
135 </body>
136 </section>
137
138 <section>
139 <title>Setting a default JRE/JDK</title>
140 <body>
141
142 <p>
143 Running the command <c>java-config --list-available-vms</c> will give you a list
144 of all available JREs and JDKs on your system. Here is an example of output:
145 </p>
146
147 <pre caption="Listing available VMs">
148 # <i>java-config --list-available-vms</i>
149 [blackdown-jdk-1.3.1] Blackdown JDK 1.3.1 (/etc/env.d/java/20blackdown-jdk-1.3.1)
150 [blackdown-jre-1.3.1] Blackdown JRE 1.3.1 (/etc/env.d/java/20blackdown-jre-1.3.1)
151 [ibm-jdk-1.3.0] IBM JDK 1.3.0 (/etc/env.d/java/20ibm-jdk-1.3.0)
152 [ibm-jdk-1.3.1] IBM JDK 1.3.1 (/etc/env.d/java/20ibm-jdk-1.3.1)
153 [ibm-jre-1.3.1] IBM JRE 1.3.1 (/etc/env.d/java/20ibm-jre-1.3.1)
154 [sun-jdk-1.4.0] Sun JDK 1.4.0 (/etc/env.d/java/20sun-jdk-1.4.0)
155 </pre>
156
157 <p>
158 The name in the brackets <path>"[]"</path> is the handle or ID for that
159 particular VM. You use pass that ID to <c>java-config --set-system-vm</c>. Here is
160 an example of how to set the system VM.
161 </p>
162
163 <pre caption="Setting the System VM">
164 # <i>java-config --set-system-vm=ibm-jdk-1.3.1</i>
165 Now using IBM JDK 1.3.1 (/etc/env.d/java/20ibm-jdk-1.3.1)
166 </pre>
167
168 <note>
169 You will have to be root to run --set-system-vm.
170 </note>
171
172 <p>
173 Once you have issued <c>java-config --set-system-vm</c> with a particular VM ID,
174 you will need to regenerate your /etc/profile.env. You can do it like this:
175 </p>
176
177 <pre caption="Regenerating /etc/profile.env" >
178 # <i>env-update</i>
179 </pre>
180
181 <p>
182 After this, you will either want to relogin, or resource
183 <path>/etc/profile</path> into your environment.
184 </p>
185
186 <p>
187 As a regular user, you can use <c>java-config --set-user-vm</c>, which will
188 create <path>~/.gentoo/java-env</path> with all required env vars. You would
189 normally source this from your shell's startup script
190 (generally <path>~/.bashrc</path>).
191 </p>
192
193 </body>
194 </section>
195
196 <section>
197 <title>Setting a default CLASSPATH</title>
198 <body>
199
200 <p>
201 <c>java-config</c> can also be used to set a system-wide default CLASSPATH, and
202 of course a user-specific default CLASSPATH.
203 </p>
204
205 <p>
206 First you want to list available java libraries that might be interesting to put
207 in your CLASSPATH. Here is an example of output:
208 </p>
209
210 <pre caption="Listing classes">
211 # <i>java-config --list-available-packages</i>
212 [bsh] BeanShell is a small, free, embeddable, Java
213 source interpreter with object scripting language
214 features. (/usr/share/bsh/package.env)
215 [oro] A set of text-processing Java classes that
216 provide Perl5 compatible regular expressions, AWK-like
217 regular expressions, glob expressions, and utility
218 classes for performing substitutions, splits, filtering
219 filenames, etc. (/usr/share/oro/package.env)
220 [bcel] The Byte Code Engineering Library: analyze, create,
221 manipulate Java class files (/usr/share/bcel/package.env)
222 [jsch] JSch is a pure Java implementation of SSH2.
223 (/usr/share/jsch/package.env)
224 ...
225 </pre>
226
227 <p>
228 Again, the name in brackets <path>"[]"</path> are the IDs that you have to pass
229 to <c>java-config --set-system-classpath</c>. Here is an example:
230 </p>
231
232 <pre caption="Setting classpaths">
233 # <i>java-config --set-system-classpath=log4j,java-gtk,java-gnome</i>
234 </pre>
235
236 <note>
237 The current directory (.) will not be part of the system classpath, as that
238 should be added in root's login profile.
239 </note>
240
241 <p>
242 Again, you will want to run <c>env-update</c> to update your system's
243 environment, and you might also want to relogin or resource the
244 <path>/etc/profile</path>.
245 </p>
246
247 <p>
248 For users, <c>java-config --set-user-classpath</c> will create
249 <path>~/.gentoo/java-env-classpath</path>, which is automatically included
250 by <path>~/.gentoo/java-env</path>.
251 </p>
252
253 </body>
254 </section>
255 </chapter>
256
257 <chapter>
258 <title>USE flags for use with Java</title>
259 <section>
260 <title>Setting USE flags</title>
261 <body>
262
263 <p>
264 For more information regarding USE flags, refer to the
265 <uri link="/doc/en/handbook/handbook-x86.xml?part=2&amp;chap=2">USE flags</uri>
266 chapter from the Gentoo Handbook.
267 </p>
268
269 </body>
270 </section>
271 <section>
272 <title>The flags</title>
273 <body>
274
275 <ul>
276 <li>The <b>java</b> flag adds support for Java in a variety of programs.</li>
277 <li>The <b>mozilla</b> flag adds support for Mozilla-like browsers (including Firefox)
278 if you are using blackdown's Java kit. You will need this for viewing Java applets
279 in your Mozilla-like browser.</li>
280 </ul>
281
282 </body>
283 </section>
284 </chapter>
285
286 <chapter>
287 <title>Additional resources</title>
288 <section>
289 <title>Off-line resources</title>
290 <body>
291
292 <ul>
293 <li>java-config man page</li>
294 <li><c>java-config --help</c></li>
295 <li>The <path>/usr/bin/java-config</path> script itself</li>
296 </ul>
297
298 </body>
299 </section>
300
301 <section>
302 <title>Online resources</title>
303 <body>
304 <ul>
305 <li>The <uri link="http://news.gmane.org/gmane.linux.gentoo.devel"
306 >gentoo-dev</uri>, <uri link="http://news.gmane.org/gmane.linux.gentoo.user"
307 >gentoo-user </uri> mailing list archives</li>
308 <li>#gentoo and #gentoo-java on irc.freenode.net</li>
309 <li><uri link="http://en.wikipedia.org/wiki/Java_programming_language">Wikipedia's entry for Java</uri></li>
310 </ul>
311
312 </body>
313 </section>
314 </chapter>
315 </guide>

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