Caching FileInputStream

Question

In my program I am repeatedly reading a number of files like this:

String myLetter = "CoverSheet.rtf"; // actually has a full path
FileInputStream in = new FileInputStream(myLetter);
letterSection.importRtfDocument(in);
in.close();

Because there are many small files which are components to add to the document with importRtfDocument, and thousands of letters to generate in a run, the processing is quite slow.

The importRtfDocument method comes from a library I'm using, and needs to be given a FileInputStream. This is where I'm stumped. I tried a few things like declaring a FileInputStream for each file in the class and keeping them open - but reset() isn't supported.

I have looked at other similar questions like this one:

How to Cache InputStream for Multiple Use

However, none seem to address my problem, to wit, how can I cache a FileInputStream?

Answer 1

I normally create my own pool to cache files. Just consider following simple code :

class CachedPool {
    private Map<URI, CachedFile> pool = new HashMap<>();

    public CachedPool(){
    }

    public <T> T getResource(URI uri) {
        CachedFile file;
        if(pool.containsKey(uri)){
            file = pool.get(uri);
        } else {
            file = new CachedFile(uri);   // Injecting point to add resources
            pool.put(uri, file);
        }
        return file.getContent();
    }
}

class CachedFile {
    private URI uri;
    private int counter;
    private Date cachedTime;
    private Object content;

    public CachedFile(URL uri){
        this.url = uri;
        this.content = uri.toURL().getContent();
        this.cachedTime = new Date();
        this.counter = 0;
    }

    public <T> T getContent(){
        counter++;
        return (T) content;
    }

    /** Override equals() and hashCode() **/
    /** Write getters for all instance variables **/
}

You can use counter of CachedFile to remove the files that are rarely being used after a certain time period or when heap memory is very low.