A data file embedded inside the jar file.
Use
You access the resource with code like this:
or this
where InWords.properties is the name of the file
inside the jar you want to read.
Class.getResource is similar, giving you the URL
of the resource instead of an InputStream to read
it. Note that getResource is an instance method. Class.getResource
makes these changes to the resource name: if the resource name starts with "/",
it is unchanged; otherwise, the package name is prepended to the resource name
after converting "." to "/". This allows you to use either
dots or slashes to separate the components of the name. So normally your
resource member name includes the package name, but you don’t specify the
package name to getResource. Alternatively, but not
recommended, you can specify the fully qualified name of the resource by using a
lead / on the name you feed to getResource.
Never use \ in resource names. So you can access by
either: /com/mindprod/entities/entitytable.ser or the
short form entitytable.ser. The short form only works
from classes in the com.mindprod.entities package.
When using Applets or Java Web Start, sometimes Thread.
currentThread(). getContextClassLoader().
getResource() works better than this.
getClass(). getClassLoader().
getResource(). This may bypass a bug in JDK 1.4
and 1.5 now fixed in 1.6+.
Recipe
Here my recipe for accessing resources:
- Using jar.exe, pack the resource in the jar under the
package name and resource name. For example, a resource for use by com.mindprod.entities.
Entities would be stored in the jar under the name com/mindprod/entities/entitytable.ser.
Note that the class name does not appear, just the package and resource name.
See jar.exe for how. Use WinZip or similar ZIP utility
to verify the package name and resource name are correct inside the jar,
including case.
- In your class, access the resource with:
URL url = Entities.class.getResource( "entitytable.ser" );
System.out.println( url );
URL url = Class.getResource( "entitytable.ser" );
Note the lack of dots, slashes, package name or class name in the resource. Dump
the URL out so you can double check where it found it.
Cramfull
The problem with resources is you must manually remember to include them. You
might not find out they are missing from the jar until months later when someone
goes to use an obscure resource. GenJar is incapable of detecting missing
resources or automatically including them. Cramfull
is a tool to convert resources into Java source code. The advantage of Cramfull
is GenJar can detect resources coded as class files and make sure they are
included.
Old Netscape
class.getResource does not work in some versions of
Netscape. You must use class.getResourceAsStream.
Further, for some Satanic reason, the folk at Netscape decided that resources
must have one of a magic list of extensions. *.com, *.exe,
*.dat are not among them. Happily *.jpg,
*.gif and *.ser are. Images
are a very common sort of resource.
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Roedy Green :
