Java文件操作案例

总结常见的文件操作、流操作的用法

文件操作

常见流

InputStream ： 是所有字节输入流的超类，一般使用它的子类：FileInputStream等，它能输出字节流；
InputStreamReader ： 是字节流与字符流之间的桥梁，能将字节流输出为字符流，并且能为字节流指定字符集，可输出一个个的字符；
BufferedReader ： 提供通用的缓冲方式文本读取，readLine读取一个文本行， 从字符输入流中读取文本，缓冲各个字符，从而提供字符、数组和行的高效读取。

流操作

InputStream inputStream = new FileInputStream(new File('/Users/xxx/test.txt'))
//groovy 自动调用 close 关闭流
inputStream.withStream { it->
   //对输入流操作
}

转换

String > InputStream

InputStream is = new ByteArrayInputStream(string.getBytes("UTF-8"));

InputStream > String

String > OutputStream

OutputStream > String

OutputStream > InputStream

ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream()
ByteArrayInputStream byteArrayInputStream =new ByteArrayInputStream(byteArrayOutputStream.toByteArray())

/**
     * 将输入流持久化到文件
     *
     * @param file        目标文件
     * @param inputStream 要持久化的输入流
     * @param append      true从头部开始覆盖目标文件内容,false 不覆盖在目标文件尾部追加
     * @param bufferSize  使用的内存缓存区大小，推荐传入   8 * 1024
     * @throws IOException
     */
    public static void inputStreamToFile(File file, InputStream inputStream, boolean append, int bufferSize) throws IOException {
        FileOutputStream fileOutputStream = new FileOutputStream(file, append);
        BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(fileOutputStream);
        byte[] data = new byte[bufferSize];
        while (inputStream.read(data) != -1) {
            bufferedOutputStream.write(data);
            bufferedOutputStream.flush();
        }
        bufferedOutputStream.close();
        fileOutputStream.close();
        inputStream.close();
    }

流的复制

import org.apache.commons.io.input.TeeInputStream;

import java.io.*;
import java.util.concurrent.CompletableFuture;
import java.util.function.Consumer;

/**
 * 流的复制，将一个InputStream变成多个InputStream
 * <p>
 * <code>
          Shunt
         .load(fileInputStream)
         .pipo(new Consumer() {
                    @Override
                    public void accept(Object o) {
                        InputStream inputStream = (InputStream) o;
                        try {
                            IOUtil.inputStreamToFile(new File("d:/bz/1.csv"), inputStream, true, 8 * 1024);
                            inputStream.close();
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }
                }, new Consumer() {
                    @Override
                    public void accept(Object o) {
                        InputStream inputStream = (InputStream) o;
                        try {
                            IOUtil.inputStreamToFile(new File("d:/bz/2.csv"), inputStream, true, 8 * 1024);
                            inputStream.close();
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }
                }
            );
 * </code>
 * <p>
 * Created by liutf on 2016/7/6 0006.
 */
public class Shunt {
    InputStream inputStream;

    public static Shunt load(InputStream inputStream) {
        return new Shunt(inputStream);
    }

    private Shunt(InputStream inputStream) {
        this.inputStream = inputStream;
    }

    private InputStream shunt(InputStream inputStream) throws IOException {
        PipedInputStream in = new PipedInputStream();
        PipedOutputStream out = new PipedOutputStream(in);
        TeeInputStream tee = new TeeInputStream(inputStream, out, true);
        this.inputStream = in;
        return tee;
    }

    public Shunt pipo(Consumer<InputStream>... consumers) throws IOException {
        for (Consumer<InputStream> consumer : consumers) {
            InputStream br = shunt(inputStream);
            CompletableFuture.runAsync(() -> {
                try {
                    consumer.accept(br);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            });
        }
        return this;
    }


}

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