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Tip of the Day
Language: Java
Expertise: Intermediate
Feb 8, 1999

Obtaining a File Path From a Class Name

You can use a basic class finder utility to find the actual class file from a class. You can use the complete utility to locate a class file (or any other file) on your operating system. The method getPathFromClassName() demonstrates how to convert a qualified package name into a qualified filesystem path name:
 
    public class ClassFinder {

      private static final String classPath=System.getProperty("java.class.path");
      private static final String fileSeparator=System.getProperty("file.separator");

      public static final String getPathFromClassName (String classname) {
        StringTokenizer st = new StringTokenizer(classname, ".");
        StringBuffer buf = new StringBuffer();

        while (st.hasMoreTokens()) {
          buf.append(st.nextToken());
          if (st.countTokens() > 0)
            buf.append(fileSeparator);
        }

        buf.append(".class");
        String className = buf.toString();

        return className;
      }

      // Method getFullPathFromFileName

      public static void main (String[] args) {
        String classPath = ClassFinder.getPathFromClassName(args[0]);
        System.out.println("\nClass path = " +  classPath);
      }
    }
Lines 2-3 obtain the JVM's current class path and the system file separator (i.e. the delimiter for separating directories in the system's file path, like "/" and "\"). Line 7 constructs a StringTokenizer for detecting the "." delimiters in a qualified class path (i.e. foo.bar.baz.MyClass). Lines 10-14 detect the "." characters and replace them with the fileSeparator. The final path name is returned on Line 19. Lines 24-26 provide the main routine for testing this method. Note that the method is static and therefore, the class doesn't have to be instantiated to be used. On a Windows system, the output on passing a string foo.bar.baz.MyClass will be:
 
foo\bar\baz\MyClass.class
See Tip "A Basic File Finder Utility" to find out how this method can be further used to obtain the complete class path for any Java class file on your system.
Ajit Sagar
 
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