Java IO.pdf - Nguyen Dang Binh

Java I/O
Notice the strange URL in the previous code. A JAR URL is like a normal HTTP or file URL
pointing to a JAR file with the prefix "jar:" added to the URL's scheme (i.e., jar:http: or
jar:file:). After the hostname, you place the pathname to the JAR file on the server. After the
JAR filename, you add an exclamation point and a path to the particular entry you want
within the JAR archive. For example, to refer to the file StreamCopier.class in the
com/macfaq/io directory of the JAR file javaio.jar located at http://www.oreilly.com/, you
would use the JAR URL
jar:http://www.oreilly.com/javaio.jar!/com/macfaq/io/StreamCopier.class. If the entry is
omitted, then the URL refers to the JAR archive as a whole; for example,
jar:http://www.oreilly.com/javaio.jar!/.
If you only want to read data from the connection using getInputStream() from the
URLConnection superclass, the previous code will suffice. If you want to use the methods of
the JarURLConnection class directly, then you should cast the object returned from
openConnection() to JarURLConnection. For example:
try {
URL u = new URL(
"jar:http://www.oreilly.com/javaio.jar!/com/macfaq/io/StreamCopier.class");
JarURLConnection juc = (JarURLConnection) u.openConnection();
// ...
}
catch (MalformedURLException e) {
// ...
}
Once you've done this, you can use eight methods that provide easy access to various metainformation
about the JAR file and its contents. This meta-information comes from the
archive's manifest or certificate files. The getJarFileURL() method returns the URL of the
JAR file for this connection:
public URL getJarFileURL()
This is most useful if the URL refers to a particular entry in the file. In that instance, the URL
returned by getJarFileURL() refers to the URL of the archive. For example:
URL u = new URL(
"jar:http://www.oreilly.com/javaio.jar!/com/macfaq/io/StreamCopier.class");
JarURLConnection juc = (JarURLConnection) u.openConnection();
URL base = juc.getURL();
The URL object base now refers to http://www.oreilly.com/javaio.jar.
The getEntryName() method returns the name of the JAR entry this JAR URL refers to. It
returns null if the JAR URL points to a JAR file as a whole rather than to one of the entries
in the file.
public String getEntryName()
The getJarFile() method returns an immutable JarFile object for the JAR archive referred
to by this URL. You can read the state of this object, but you cannot change it. Attempts to do
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