我应该缓冲InputStream还是InputStreamReader？ [英] Should I buffer the InputStream or the InputStreamReader?

问题描述

以下两种缓冲方法之间有什么区别（如果有的话）？

What are the differences (if any) between the following two buffering approaches?

Reader r1 = new BufferedReader(new InputStreamReader(in, "UTF-8"), bufferSize);
Reader r2 = new InputStreamReader(new BufferedInputStream(in, bufferSize), "UTF-8");

推荐答案

r1 效率更高。 InputStreamReader 本身没有大缓冲区。可以将 BufferedReader 设置为具有比 InputStreamReader 更大的缓冲区。 r2 中的 InputStreamReader 将成为瓶颈。

r1 is more efficient. The InputStreamReader itself doesn't have a large buffer. The BufferedReader can be set to have a larger buffer than InputStreamReader. The InputStreamReader in r2 would act as a bottleneck.

坚果：你应该通过漏斗读取数据，而不是通过瓶子。

In a nut: you should read the data through a funnel, not through a bottle.

更新：这是一个小基准程序，只是复制'n'paste'n'run它。您不需要准备文件。

Update: here's a little benchmark program, just copy'n'paste'n'run it. You don't need to prepare files.

package com.stackoverflow.q3459127;

import java.io.BufferedInputStream;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.Reader;

public class Test {

    public static void main(String... args) throws Exception {

        // Init.
        int bufferSize = 10240; // 10KB.
        int fileSize = 100 * 1024 * 1024; // 100MB.
        File file = new File("/temp.txt");

        // Create file (it's also a good JVM warmup).
        System.out.print("Creating file .. ");
        BufferedWriter writer = null;
        try {
            writer = new BufferedWriter(new FileWriter(file));
            for (int i = 0; i < fileSize; i++) {
                writer.write("0");
            }
            System.out.printf("finished, file size: %d MB.%n", file.length() / 1024 / 1024);
        } finally {
            if (writer != null) try { writer.close(); } catch (IOException ignore) {}
        }

        // Read through funnel.
        System.out.print("Reading through funnel .. ");
        Reader r1 = null;        
        try {
            r1 = new BufferedReader(new InputStreamReader(new FileInputStream(file), "UTF-8"), bufferSize);
            long st = System.nanoTime();
            for (int data; (data = r1.read()) > -1;);
            long et = System.nanoTime();
            System.out.printf("finished in %d ms.%n", (et - st) / 1000000);
        } finally {
            if (r1 != null) try { r1.close(); } catch (IOException ignore) {}
        }

        // Read through bottle.
        System.out.print("Reading through bottle .. ");
        Reader r2 = null;        
        try {
            r2 = new InputStreamReader(new BufferedInputStream(new FileInputStream(file), bufferSize), "UTF-8");
            long st = System.nanoTime();
            for (int data; (data = r2.read()) > -1;);
            long et = System.nanoTime();
            System.out.printf("finished in %d ms.%n", (et - st) / 1000000);
        } finally {
            if (r2 != null) try { r2.close(); } catch (IOException ignore) {}
        }

        // Cleanup.
        if (!file.delete()) System.err.printf("Oops, failed to delete %s. Cleanup yourself.%n", file.getAbsolutePath());
    }

}

我的Latitude E5500上的结果 Seagate Momentus 7200.3 硬盘：

Results at my Latitude E5500 with a Seagate Momentus 7200.3 harddisk:

Creating file .. finished, file size: 99 MB.
Reading through funnel .. finished in 1593 ms.
Reading through bottle .. finished in 7760 ms.

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