Read InputStream to String

There are many ways to convert an InputStream (whether FileInputStream, SocketInputStream or others) to a String, StringBuffer or StringBuilder.

I implemented some of them and benchmarked them. Here’s the code:

package com.eaio.perftest;

import java.io.BufferedInputStream;
import java.io.BufferedReader;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;

import org.junit.Test;


public class StreamToStringTest {
    
    private final File testFile = new File("testfile.txt");
    
    private final int runs = 100;
    
    @Test
    public void variousMethods() throws IOException {
        long then;
        
        then = System.currentTimeMillis();
        for (int i = 0; i < runs; ++i) {
            byteByByteIntoByteArrayToString();
        }
        System.out.println("byteByByteIntoByteArrayToString(): " + (System.currentTimeMillis() - then) + " ms");
        
        then = System.currentTimeMillis();
        for (int i = 0; i < runs; ++i) {
            byteByByteIntoCommonsIOByteArrayToString();
        }
        System.out.println("byteByByteIntoCommonsIOByteArrayToString(): " + (System.currentTimeMillis() - then) + " ms");

        then = System.currentTimeMillis();
        for (int i = 0; i < runs; ++i) {
            charByCharReadingIntoStringBuffer();
        }
        System.out.println("charByCharReadingIntoStringBuffer(): " + (System.currentTimeMillis() - then) + " ms");

        then = System.currentTimeMillis();
        for (int i = 0; i < runs; ++i) {
            charByCharReadingIntoStringBuffer();
        }
        System.out.println("charByCharReadingIntoStringBuilder(): " + (System.currentTimeMillis() - then) + " ms");

        then = System.currentTimeMillis();
        for (int i = 0; i < runs; ++i) {
            bufferedIntoStringBuilder();
        }
        System.out.println("bufferedIntoStringBuilder(): " + (System.currentTimeMillis() - then) + " ms");

        then = System.currentTimeMillis();
        for (int i = 0; i < runs; ++i) {
            bufferedReaderCharByCharIntoStringBuilder();
        }
        System.out.println("bufferedReaderCharByCharIntoStringBuilder(): " + (System.currentTimeMillis() - then) + " ms");

        then = System.currentTimeMillis();
        for (int i = 0; i < runs; ++i) {
            bufferedStreamCharByCharIntoStringBuilder();
        }
        System.out.println("bufferedStreamCharByCharIntoStringBuilder(): " + (System.currentTimeMillis() - then) + " ms");

        
    }

    private void bufferedStreamCharByCharIntoStringBuilder() throws IOException {
        InputStream stream = new BufferedInputStream(new FileInputStream(testFile), 4096);
        Reader reader = new InputStreamReader(stream, "UTF-8");
        StringBuilder builder = new StringBuilder();
        int c;
        while ((c = reader.read()) != -1) {
            builder.append((char) c);
        }
        reader.close();
        builder.toString();
    }
    
    private void bufferedReaderCharByCharIntoStringBuilder() throws IOException {
        InputStream stream = new FileInputStream(testFile);
        Reader reader = new BufferedReader(new InputStreamReader(stream, "UTF-8"));
        StringBuilder builder = new StringBuilder();
        int c;
        while ((c = reader.read()) != -1) {
            builder.append((char) c);
        }
        reader.close();
        builder.toString();
    }

    private void bufferedIntoStringBuilder() throws IOException {
        InputStream stream = new FileInputStream(testFile);
        StringBuilder builder = new StringBuilder();
        byte[] buf = new byte[4096];
        int b;
        while ((b = stream.read(buf)) != -1) {
            builder.append(new String(buf, 0, b, "UTF-8"));
        }
        stream.close();
        builder.toString();
    }

    private void byteByByteIntoCommonsIOByteArrayToString() throws IOException {
        InputStream stream = new FileInputStream(testFile);
        org.apache.commons.io.output.ByteArrayOutputStream out = new org.apache.commons.io.output.ByteArrayOutputStream();
        int b;
        while ((b = stream.read()) != -1) {
            out.write(b);
        }
        stream.close();
        new String(out.toByteArray(), "UTF-8");
    }

    private void byteByByteIntoByteArrayToString() throws IOException {
        InputStream stream = new FileInputStream(testFile);
        ByteArrayOutputStream out = new ByteArrayOutputStream() {

            @Override
            public synchronized byte[] toByteArray() {
                return this.buf;
            }
            
        };
        int b;
        while ((b = stream.read()) != -1) {
            out.write(b);
        }
        stream.close();
        new String(out.toByteArray(), "UTF-8");
    }
    
    private void charByCharReadingIntoStringBuffer() throws IOException {
        InputStream stream = new FileInputStream(testFile);
        Reader reader = new InputStreamReader(stream, "UTF-8");
        StringBuffer buffer = new StringBuffer();
        int c;
        while ((c = reader.read()) != -1) {
            buffer.append((char) c);
        }
        reader.close();
        buffer.toString();
    }

    private void charByCharReadingIntoStringBuilder() throws IOException {
        InputStream stream = new FileInputStream(testFile);
        Reader reader = new InputStreamReader(stream, "UTF-8");
        StringBuilder buffer = new StringBuilder();
        int c;
        while ((c = reader.read()) != -1) {
            buffer.append((char) c);
        }
        reader.close();
        buffer.toString();
    }
    
}

On this Windows XP box that has a fast RunCore Pro IV SSD in it, bufferedIntoStringBuilder is the fastest.

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Johann Burkard, @johannburkard
Teisendorf, Germany
N 47° 51' 5.904", E 12° 49' 0.012"