1 This file contains some information on the essential concepts and principles
2 involved in the use of this software.
3
4 Installation
5 ------------
6
7 To build the software, perhaps as part of a packaging process, you can run the
8 following command:
9
10 python setup.py build
11
12 To directly install the software in a system-wide location, you can run the
13 following command:
14
15 python setup.py install
16
17 The installation adds the java and javaclass packages to your site-packages
18 directory and the runclass.py program to the same bin directory that python
19 resides in. However, it is arguably preferable to make an operating system
20 package for the software and use the system's package manager to install and
21 potentially uninstall the software.
22
23 Testing
24 -------
25
26 It should be possible to just run the test.py program and see the results:
27
28 python test.py
29
30 Contact, Copyright and Licence Information
31 ------------------------------------------
32
33 The current Web page for javaclass at the time of release is:
34
35 http://www.boddie.org.uk/python/javaclass.html
36
37 Copyright and licence information can be found in the docs directory - see
38 docs/COPYING.txt, docs/lgpl-3.0.txt and docs/gpl-3.0.txt for more information.
39
40 Dependencies
41 ------------
42
43 Python Tested with Python 2.3, although javaclass.classfile
44 should work on any recent Python 2.x release.
45
46 A Java toolchain Tested with whichever Sun JDK for Java release was current
47 in 2005. ;-)
48
49 Class Search Paths
50 ------------------
51
52 Java classes belonging to packages are located using sys.path or PYTHONPATH
53 in the same way that they would be located using the Java classpath (or
54 CLASSPATH environment variable). Thus, the rules for locating package
55 classes are as follows:
56
57 * Classes residing within plain directories which represent a package
58 hierarchy can be accessed by putting the parent directory of the top of
59 the package hierarchy on the PYTHONPATH (or sys.path). For example, a
60 package called mypackage, represented by a directory of the same name at
61 /home/java/classes/mypackage, would be made accessible by adding the
62 /home/java/classes directory to the PYTHONPATH.
63
64 * Classes residing within .jar files can be accessed by putting the path to
65 each .jar file on the PYTHONPATH. For example, a package called
66 mypackage, represented by a file located at /home/java/lib/mypackage.jar,
67 would be made accessible by adding the /home/java/lib/mypackage.jar file
68 to the PYTHONPATH.
69
70 Note that classes not belonging to a package cannot be accessed via such
71 search paths and are made available using a special module (see "Non-package
72 Classes" below).
73
74 Importing Classes
75 -----------------
76
77 In Python, the following statement should be enough to enable Java class
78 import:
79
80 import javaclass.classhook
81
82 (Other modules reside in the javaclass package, so it is possible to access
83 them without changing Python's import mechanisms, should such modification
84 be undesirable or unnecessary.)
85
86 Importing Non-package Classes
87 -----------------------------
88
89 Classes which do not belong to a package are only accessible when residing
90 in the current working directory of any program attempting to use them. Such
91 classes will not be made available automatically, but must be imported from
92 a special module called __this__.
93
94 * Usage of the "import __this__" statement will cause all classes in the
95 current directory to be made available within the __this__ module.
96
97 * Usage of the "from __this__ import" construct will cause all classes in
98 the current directory to be processsed, but only named classes will be
99 made available in the global namespace unless "*" was specified (which
100 will, as usual, result in all such classes being made available).
101
102 Running Java Classes
103 --------------------
104
105 Java classes with a public, static main method can be run directly using the
106 runclass.py program.
107
108 * Free-standing classes (ie. not belonging to packages) can be run from
109 the directory in which they reside. For example, suitable classes in the
110 tests directory would be run as follows:
111
112 cd tests
113 runclass.py MainTest hello world
114
115 * Classes residing in packages can be run by ensuring that the packages
116 are registered on the PYTHONPATH (see "Class Search Paths" above). Then,
117 the testpackage.MainTest class (for example) would be run as follows:
118
119 runclass.py testpackage.MainTest hello world
120
121 Accessing Python Libraries from Java
122 ------------------------------------
123
124 To wrap Python libraries for use with Java, skeleton classes need to be
125 compiled corresponding to each of the wrapped classes. Each of the methods
126 in the skeleton classes can be empty (or return any permissible value) since
127 the only purpose they serve is to provide the Java compiler with information
128 about the Python libraries.
129
130 1. Compile the skeleton classes:
131
132 javac examples/Tkinter/tkjava/*.java
133
134 2. Compile the Java classes which use the wrapped Python libraries:
135
136 javac -classpath examples/Tkinter examples/Tkinter/Application.java
137
138 3. Run the wrap.py tool on the directory where the skeleton class files
139 reside, providing the name of the Python package or module being
140 wrapped. This converts the directory into a Python package:
141
142 python tools/wrap.py examples/Tkinter/tkjava Tkinter
143
144 Since the Java class files, if left in the processed directory, would
145 be detected and imported using the special import hook, and since this
146 would result in two conflicting implementations being imported (with
147 possibly the non-functional Java classes being made available instead
148 of the generated wrapper classes), the wrap.py tool removes all
149 processed class files, leaving only Python source files in the
150 processed directory.
151
152 4. The Java classes which use the wrapped Python libraries can now be
153 imported and used as described above. The wrapper package (tkjava in
154 the above example) needs to reside in sys.path or PYTHONPATH, as must
155 the wrapped library (Tkinter in the above example).
156
157 cd examples/Tkinter
158 runclass.py Application
159
160 Issues
161 ------
162
163 Fix the class initialisation so that non-Java classes (and already imported
164 classes) are obtained. Prevent re-entry into module importing for modules
165 already being imported (if this is not handled already by the Python import
166 mechanisms).
167
168 Implement better importing mechanisms so that circular module dependencies
169 can be avoided. For example, when dealing with java.lang classes which
170 depend on java.security classes which then inherit from java.lang.Object,
171 the classes should all be imported but only initialised after no more
172 importing is necessary. Since usage of external names is recorded in the
173 bytecode translation process, it should be possible to reach such a
174 condition definitively.
175
176 The test program crashes, fairly quickly under Python 2.4, too. There seems
177 to be some kind of memory allocation problem.
178
179 Investigate better exception raising. Currently, exceptions have to be
180 derived from object so that object.__new__ can be used upon them. However,
181 this seems to prevent them from being raised, and they need to be wrapped
182 within Exception so that the information can be transmitted to the
183 exception's handler.
184
185 Consider nicer ways of writing the method names in Python, perhaps using a
186 function which takes the individual parameter types as arguments.
187
188 New in javaclass 0.2 (Changes since javaclass 0.1)
189 --------------------------------------------------------
190
191 * Added Braden Thomas' class file serialisation patches.
192 * Relicensed under the LGPL version 3 or later.
193
194 Release Procedures
195 ------------------
196
197 Update the javaclass/__init__.py __version__ attribute.
198 Update the release notes (see above).
199 Update the setup.py and PKG-INFO files.
200 Check the setup.py file and ensure that all package directories are
201 mentioned.
202 Tag, export.
203 Archive, upload.