Download Packaging, Resources and Components The standard way to

Packaging, Resources and Components
It is transportable
The standard way to package Java is
the jar-file. JAR stands for Java
Archive.
It supports hierarchical directories
A jar-file is a container for sourcefiles,
classfiles and other files. Technically a
jar-file is a zip-file with some special
files included.
Selfdescribing via a manifest file.
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Allows more efficient transferring
Compressed
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The manifest is a file in the catalogue
META-INF. It is a text file that
describes the files in the archive
jar-files are created with the jar tool. It
works mostly like the UNIX tar tool.
To create one you do
JAR-files can be signed which means
that it has been signed with a private
key. To read such a file you need access
to the corresponding public key. This is
to certify the creator of the file.
jar cf <jar-output-file> <class-files...>
eg
jar cf Myjar.jar ClassA.class
ClassB.class
To extract something you can do
jar xf <jar-file> <class-file>
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The class loader can handle jar-files,
this means that all standard packages
are delivered as jar-files. They need not
be unpacked.
An important feature in modern programming is component technique. A
component is a reusable piece of software with a well-defined behavior.
It is somewhat equivalent to electronic
components that have a well-defined
interface and that can be combined to
make some complex item. If you find a
faster or cheaper component with the
same interface you just replaces the old
one.
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The Java component is the Bean. A
Bean is no extension of some Beanclass or an implementaion of some
Bean-interface. It is just one or more
classes that adheres to a certain protocol.
Some requirements on a Bean:
Must be Serializable
Must have a parameterless constructor
Naming conventions of the instance
variables and other resources
Getter and setter method for resources.
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How Java Beans work
What should be made into a Bean?
They must be Serializable, this is
because they might be saved into some
object database.
All classes can be made into a Bean but
the most important ones are those that
have a good chance to be reused by
others. This includes utility classes that
needs to be customized etc.
They must have a standard constructor
to be instansiable
The resources and variables should be
named xyz. There should be getter
methods named as getXyz and setters
called setXyz.
Tools that works with Beans uses a special technique called introspection.
Introspection can be used to inspect a
component to find out its methods,
variables and other resources.
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A simple Bean might look like
Compile it with
import java.awt.*;
import java.io.Serializable;
javac SimpleBean.java
public class SimpleBean extends Canvas implements
Serializable {
Create a manifest file with the content
private Color color = Color.green;
Name: SimpleBean.class
Java-Bean: True
public SimpleBean() {
setSize(60,40);
setBackground(Color.red);
}
public Color getColor() {
return color;
}
Create a jar file to be used in the Bean
tool.
public void setColor(Color newColor) {
color = newColor;
repaint();
}
jar cfm SimpleBean.jar manifest.tmp
SimpleBean.class
public void paint(Graphics g) {
g.setColor(color);
g.fillRect(20, 5, 20, 30);
}
}
All Bean requirements are fulfilled by
this class.
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Internationalization (i18n)
and localiation (l10n)
However to use formatting of items
like dates, numbers etc, we have to use
the capabilities of Java.
An example of simple multilanguage
page can be
There is support in webcontainer to
generate text in different languages.
Modern browsers can also display
many languages.
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A simple servlet that produces this is
package serv;
import
import
import
import
import
javax.servlet.*;
javax.servlet.http.*;
java.io.*;
java.text.*;
java.util.*;
public class Serv extends HttpServlet {
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws IOException, ServletException {
Locale locale;
DateFormat full;
response.setContentType(
"text/plain;charset=UTF-8");
PrintWriter out = response.getWriter();
locale = new Locale("en", "US");
full =
DateFormat.getDateTimeInstance(DateFormat.LONG,
DateFormat.LONG,
locale);
out.println("In English:");
out.println("Hello World");
out.println(full.format(new Date()));
out.println();
locale = new Locale("es", "");
full =
DateFormat.getDateTimeInstance(DateFormat.LONG,
DateFormat.LONG,
locale);
out.println("En Espa\u00f1ol:");
out.println("\u00a1Hola Mundo!");
out.println(full.format(new Date()));
out.println();
locale = new Locale("ja", "");
full =
DateFormat.getDateTimeInstance(DateFormat.LONG,
DateFormat.LONG,
locale);
out.println("In Japanese:");
out.println("\u4eca\u65e5\u306f\u4e16\u754c");
out.println(full.format(new Date()));
out.println();
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locale = new Locale("zh", "");
full =
DateFormat.getDateTimeInstance(DateFormat.LONG,
DateFormat.LONG,
locale);
out.println("In Chinese:");
out.println("\u4f60\u597d\u4e16\u754c");
out.println(full.format(new Date()));
out.println();
locale = new Locale("ko", "");
full =
DateFormat.getDateTimeInstance(DateFormat.LONG,
DateFormat.LONG,
locale);
out.println("In Korean:");
out.println(
"\uc548\ub155\ud558\uc138\uc694\uc138\uacc4");
out.println(full.format(new Date()));
out.println();
Some problems with internationalization:
Character encoding.
How to select language
How to implement multilingual applications.
locale = new Locale("ru", "");
full =
DateFormat.getDateTimeInstance(DateFormat.LONG,
DateFormat.LONG,
locale);
out.println("In Russian (Cyrillic):");
out.print(
"\u0417\u0434\u0440\u0430\u0432\u0441\u0442");
out.println(
"\u0432\u0443\u0439,\u041c\u0438\u0440");
out.println(full.format(new Date()));
}
public void doPost(HttpServletRequest request,
HttpServletResponse response)
throws IOException, ServletException {
doGet(request, response);
}
}
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Most modern browsers supports the
UTF-8 character set. This means that
almost any language can be coded.
Language detection:
•
•
Inquire, ask the user about preferred
language
HTTP accept-language and
accept-charset headers
String prefLang =
request.getHeader(
“accept-language”);
String prefCharset =
request.getHeader(
“accept-charset”);
•
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URL-encoding, encode the preferred
language in the URL
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Multilingual applications:
•
•
Separate pages for each language
Separate the content from the formatting. Use resource bundles and/or
style-sheets (eg XSL)
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A Resource Bundle is a collection of
resources or resource names. Given a
bundle, and a name of a resource you
can get the value of that resource.
There is an abstract class ResourceBundle that have a static method getBundle that can obtain the value of a
given resource
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There are two kinds of resource bundles
The name of a subclass should be
<bundle-name>_<locale>, eg
MyResources_sv_SE. A property file
uses the same convention but ending in
.properties.
A subclass of ResourceBundle, according to certain conventions
A resource.properties file according to
certain naming convention.
For example you can have two files
MessageBundle_en_US.properties
MessageBundle_fr_FR.properties
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They contain
Then you can use it as this
greetings = Hello
farewell = Goodbye
inquiry = How are you?
Locale currentLocale;
ResourceBundle messages;
currentLocale = new Locale(
language, country);
resp
greetings = Bonjour
farewell = Au revoir
inquiry = Comment allez-vous?
messages =
ResourceBundle.getBundle(
“MessageBundle”,
currentlocale);
System.out.println(
messages.getString(“greetings”));
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A more static way to do the same thing
is to use a class instead.
public class MessageBundle_en_US
extends ListResourceBundle {
// according to the protocol
public Object [][] getContents()
{
return contents;
}
You can then do
ResourceBundle messages =
ResourceBundle.getBundle(
“MessageBundle”,
currentLocale);
System.out.println(
messages.getString(“greetings”));
private static Object [][] contents =
{
{“greetings” , “Hello”},
{“farewell” = “Goodbye”},
{“inquiry” = “How are you?”}
};
}
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JSTL do contain i18n Tags. We will discuss JSTL later but:
<%@ taglib uri=”http://java.sun.com/jsp/jstl/fmt”
prefix=”fmt”%>
<fmt:bundle basename=”Messagebundle”>
<html>
<head>
<title>
<fmt:message key=”greetings”/>
</title>
....
</fmt:bundle>
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