编写一个介于charstreams输入供应商和输出供应商之间的过滤器

Question

I would like to write a grep type filter that takes a Guava Charstreams InputSupplier as an input and uses a Charstreams OutputSupplier as its output. It should only pass lines from the inputsupplier to the outputsupplier if they satisfy a particular regular expression.

What is the correct design pattern/paradim for doing this?

I would guess you would do the line filter like this:

InputSupplier<InputStreamReader> ris = CharStreams.newReaderSupplier(....
CharStreams.readLines(ris, new LineProcessor<....

and implementing the LineProcessor methods.

But what should the LineProcessor.getResult() return - just a succcess of failure? Should I be using a 'final' outputsupplier in the surrounding function?

Or am I using completely the wrong api/approach!!

A bit of pseudocode to demonstrate the best way would be much appreciated.

Thanks for your suggestions.

Answer 1

CharStreams.readLines returns a List<String> . So according to source code it is asking LineProcessor to accumulate lines and then return the result. In my opinion your LineReader can be something as below

new LineProcessor<List<String>>() {

    List<String> result = Lists.newArrayList();

    public boolean processLine(String line) {
      if (line matches regex){
        result.add(line.trim());
      }

      return true;//continue processing

    }

    public List<String> getResult() {return result;}

  });