Input and Output - Java - page 422

Solution

Use getClass() or getClassLoader() and either getResource() or getRe-
sourceAsStream() .

Discussion

There are three varieties of getResource() methods, some of which exist (with the exact
same signature) both in the Class class (see Chapter 23 ) and in the ClassLoader class (see
Constructing a Class from Scratch with a ClassLoader ). The methods in Class delegate to
the ClassLoader , so there is little difference between them. The methods are summarized in
Table 10-4 .

Table 10-4. The getResource* methods

Method signature In Class In ClassLoader

Y Y

public InputStream getResourceAsStream(String);

Y Y public URL getResource(String);

public Enumeration<URL> getResources(String) throws IOException; N

Y

The first is designed to quickly and easily locate a “resource” or file on your classpath. Using
the Class version, or the other one with a standard classloader implementation, the resource
can be a physical file, or a file inside a JAR file. If you define your own classloader, your
imagination is the limit, as long as it can be represented as an InputStream . This is com-
monly used as:

InputStream is = getClass (). getResourceAsStream ( "foo.properties" );
// then do something with the InputStream...

The second form returns a URL , which again, can be interpreted in various ways (see the dis-
cussion of reading from a URL in REST Web Service Client ).

The third form, only usable with a ClassLoader instance, returns an Enumeration of URL
objects. This is intended to return all the resources that match a given string; remember that a
CLASSPATH can consist of pretty much any number of directories and/or JAR files, so this