bufferedreader - read into stringbuffer and not string

Question

I have the following code. What I would like to do is read each line from the BufferedReader directly into a StringBuffer to reduce memory overhead. Once it gets to the end of the data stream I would like it to exit the while loop.

StringBuffer line = new StringBuffer();
        URL url = new URL("a url");
        BufferedReader reader = new BufferedReader(new InputStreamReader(url.openStream()));
                int count = 0;
                while(line.append(reader.readLine()) != null){
                    System.out.println(line.toString());
                    line.delete(0,line.length());
                }

It reads the stream fine but when I get to the end of the stream it returns null and keeps printing null without exiting the loop. Any

I think that use for(String line; (line = reader.readLine()) != null;) { ... } only create references. — Paul Vargas
– Paul Vargas, Commented Feb 1, 2013 at 0:10
Why are you reading into a StringBuffer only to delete it after printing out the line. Why not just print the line directly out? — Marc Baumbach
– Marc Baumbach, Commented Feb 1, 2013 at 0:11
Q. How can the result of append() ever be null? A. It can't. — user207421
– user207421, Commented Feb 1, 2013 at 0:13

MadProgrammer · Accepted Answer · 2013-02-01 00:12:39Z

4

This while(line.append(reader.readLine()) != null) is basically the same as saying while(line.append(reader.readLine()).toString() != null) which is never likely to happen.

The other problem you might have, is null is actually being translated to a literal String of "null". That's why it's printing "null", the value isn't actually null - confused yet...

Instead, try something like...

String text = null;
while((text = reader.readLine()) != null){
    line.append(text)
    System.out.println(line.toString());
    line.delete(0,line.length());
}

Updated

While I'm here, I might suggest that you are actually not saving your self anything.

readLine will create String object, which you're putting into a StringBuffer. You're not actually saving any memory, but rather complicating the process.

If you're really worried about creating lots of String objects in memory, then use BufferedReader#read(char[]) instead. Append the resulting character array to the StringBuffer.

Also, unless you need synchronized access to the StringBuffer, use StringBuilder instead, it's faster.

answered Feb 1, 2013 at 0:12

MadProgrammer

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2 Comments

user1958884 Over a year ago

I am reading into a stringbuffer and the using split(",") which goes into an array. I could be reading up to and more than a 1000 lines so I would like to keep memory usage down. But I'll try the char suggestion.

MadProgrammer Over a year ago

You have to realize the reader.readLine() has already create a String object, so any benefit you think you're getting from using a StringBuffer is negotiable. Having said that String = String + String ends up creating one additional String object per concatenation (I think 3 in that example), so you are saving your self a little

user1958884 · Accepted Answer · 2013-02-01 00:31:56Z

1

This works perfectly. You just have to catch the NUllPointerException

while(line.append(reader.readLine().toString()) != null){

answered Feb 1, 2013 at 0:31

user1958884

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3 Comments

MadProgrammer Over a year ago

Does it, as far as I'm, aware, StringBuffer will convert the null value to a String literal of "null"

MadProgrammer Over a year ago

That's weird, cause System.out.println(new StringBuffer().append((String)null).toString() == null) returns false for me

MadProgrammer Over a year ago

Actually, now I read it :P, reader.readLine().toString() would raise a NullPointerException

mfaerevaag · Accepted Answer · 2013-02-01 00:13:03Z

0

You could try the same with this for-loop:

for (String line; (line = reader.readLine()) != null;) {
    System.out.println(line); // Or whatever
}

answered Feb 1, 2013 at 0:13

mfaerevaag

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