Android Reading from an Input stream efficiently

Question

The problem in your code is that it's creating lots of heavy String objects, copying their contents and performing operations on them. Instead, you should use StringBuilder to avoid creating new String objects on each append and to avoid copying the char arrays. The implementation for your case would be something like this:

BufferedReader r = new BufferedReader(new InputStreamReader(inputStream));
StringBuilder total = new StringBuilder();
for (String line; (line = r.readLine()) != null; ) {
    total.append(line).append('\n');
}

You can now use total without converting it to String, but if you need the result as a String, simply add:

String result = total.toString();

I'll try to explain it better...

• a += b (or a = a + b), where a and b are Strings, copies the contents of both a and b to a new object (note that you are also copying a, which contains the accumulated String), and you are doing those copies on each iteration.
• a.append(b), where a is a StringBuilder, directly appends b contents to a, so you don't copy the accumulated string at each iteration.

Have you tried the built in method to convert a stream to a string? It's part of the Apache Commons library (org.apache.commons.io.IOUtils).

Then your code would be this one line:

String total = IOUtils.toString(inputStream);

The documentation for it can be found here: http://commons.apache.org/io/api-1.4/org/apache/commons/io/IOUtils.html#toString%28java.io.InputStream%29

The Apache Commons IO library can be downloaded from here: http://commons.apache.org/io/download_io.cgi

Another possibility with Guava:

dependency: compile 'com.google.guava:guava:11.0.2'

import com.google.common.io.ByteStreams;
...

String total = new String(ByteStreams.toByteArray(inputStream ));

I believe this is efficient enough... To get a String from an InputStream, I'd call the following method:

public static String getStringFromInputStream(InputStream stream) throws IOException
{
    int n = 0;
    char[] buffer = new char[1024 * 4];
    InputStreamReader reader = new InputStreamReader(stream, "UTF8");
    StringWriter writer = new StringWriter();
    while (-1 != (n = reader.read(buffer))) writer.write(buffer, 0, n);
    return writer.toString();
}

I always use UTF-8. You could, of course, set charset as an argument, besides InputStream.

What about this. Seems to give better performance.

byte[] bytes = new byte[1000];

StringBuilder x = new StringBuilder();

int numRead = 0;
while ((numRead = is.read(bytes)) >= 0) {
    x.append(new String(bytes, 0, numRead));
}

Edit: Actually this sort of encompasses both steelbytes and Maurice Perry's