Single responsibility principle

Single responsibility principle

Recently i needed to compile our all jasper-report files during application start-up.
I was modifying existing code-base to enable precompiling xml reports to binary .jreport files.

It was simple enough, traverse all *.jrxml files at a certain directory and use net.sf.jasperreports.engine.JasperCompileManager to do the actual compiling.

Here is how i traversed all files under a directory.

    private void visitAllFiles(File dir)  {
        if (dir.isDirectory()) {
            String[] children = dir.list();
            for (int i = 0; i < children.length; i++) {
                visitAllFiles(new File(dir, children[i]));
            }
        } else {
            //doSomething();
       }   
}

Here is what is wrong with this version.

The infrastructure logic to traverse the files and business logic to compile reports resides in same class.

If i needed traverse files for something else (for example to backup old compiled reports) i would need to duplicate infrastructure logic.

It seems this class is trying to do too many things. I separated this class to a reusable FileCrawler and FileVisitor.

 

public interface FileVisitor {
    void visit(File fileToProcess) ;
}

FileCrawler takes a visitor and calls visit method for each file it encounters.

     
    public FileCrawler(final File root, final FileVisitor visitor) {
       this.visitor = visitor;
    }

    private void visitAllFiles(File dir)  {
        if (dir.isDirectory()) {
            String[] children = dir.list();
            for (int i = 0; i < children.length; i++) {
                visitAllFiles(new File(dir, children[i]));
            }
        } else {
            visitor.visit(dir);
        }
    }

Usage is as follows:

  new FileCrawler(new File(this.cacheFilePath), new ReportCompiler()).start();

ReportCompiler implements FileVisitor and looks like as follows:

public void visit(File fileToProcess)  {
        String name = fileToProcess.getName();
        if (name.endsWith(".jrxml")){
            compileReport(fileToProcess.getParent(),name);
        }
}

Now i can  use anonymous inner classes to create simple reusable directory traversing logic.

new FileCrawler (new File (root), new FileVisitor() {
            public void visit(File fileToProcess) {
                String name = fileToProcess.getName();
                if (name.endsWith(".jreport")){
                    fileToProcess.delete();
                }
            }
        });