BufferedInputStream将byte []通过Socket发送到数据库

Question

我一直在寻找答案,但实际上找不到任何东西.今天早些时候,我问我如何通过字节数组将文件转换为字符串,然后再返回,以便稍后检索.

人们告诉我的是,我必须只存储字节数组,以避免令人讨厌的编码问题.所以现在我已经开始研究了这个问题,但现在我已经碰壁了.

基本上,我之前使用过无缓冲的流,将文件转换为字节数组.这在理论上很好用,但它会占用大量内存,最终会导致堆大小异常.我应该使用缓冲流(或者我被告知),而我现在遇到的问题是从BufferedInputStream到byte [].我试图复制并使用本文档中的方法

http://docs.guava-libraries.googlecode.com/git/javadoc/index.html?com/google/common/io/package-summary.html

我为缓冲流交换无缓冲流的地方.唯一的问题是,我不能直接将缓冲输出流转换为字节数组,因为我可以使用无缓冲的流.

救命？:)

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;

public final class BufferedByteStream {

    private static final int BUF_SIZE = 1024000;

    public static long copy(BufferedInputStream from, BufferedOutputStream to) throws IOException { 
        byte[] buf = new byte[BUF_SIZE];
        long total = 0;
        while(true) {
            int r = from.read(buf);
            if(r == -1) {
                break;
            }
            to.write(buf, 0, r);
            total += r;
        }
        return total;
    }

    public static byte[] toByteArray(BufferedInputStream in) throws IOException {
        BufferedOutputStream out = new BufferedOutputStream(new ByteArrayOutputStream());
        copy(in, out);
        return out. // <--- Problem is here
    }
}

编辑:

我仍然遇到堆空间错误.所以我现在发布所有代码:

main.java

import java.io.*;
import java.util.logging.Level;
import java.util.logging.Logger;
import jserver.io.BufferedByteStream;
/**
*
* @author Vipar
*/
public class main {
    public static void main(String[] args) {
    File f = new File("<doesn't matter>");
        try {
            byte[] buf;
            try (BufferedInputStream bis = new BufferedInputStream(new FileInputStream(f))) {
                buf = BufferedByteStream.toByteArray(bis);
                bis.close();
            }
            File f2 = new File("<doesn't matter>");
            try (FileOutputStream fos = new FileOutputStream(f2)) {
                fos.write(buf);
                fos.close();
            }
        } catch (FileNotFoundException ex) {
            Logger.getLogger(main.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IOException ex) {
            Logger.getLogger(main.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
}

BufferedByteStream.java

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;

public final class BufferedByteStream {

    private static final int BUF_SIZE = 1024000;

    public static long copy(BufferedInputStream from, BufferedOutputStream to) throws IOException { 
        byte[] buf = new byte[BUF_SIZE];
        long total = 0;
        while(true) {
            int r = from.read(buf);
            if(r == -1) {
                break;
            }
            to.write(buf, 0, r);
            total += r;
        }
        return total;
    }

    public static byte[] toByteArray(BufferedInputStream in) throws IOException {
        ByteArrayOutputStream bytesOut = new ByteArrayOutputStream();
        BufferedOutputStream out = new BufferedOutputStream(bytesOut);
        copy(in, out);
        return bytesOut.toByteArray();
    }
}

Answer 1

看看ByteArrayOutputStream: Java 7 API java.io.ByteArrayOutputStream

bytesOut = new ByteArrayOutputStream();
byte[] bytes = bytesOut.toByteArray();

更新:如果你坚持做你正在做的事情,你可以将中间的ByteArrayOutputStream分配给一个变量并以这种方式获取数组:

ByteArrayOutputStream bytesOut = new ByteArrayOutputStream()
BufferedOutputStream out = new BufferedOutputStream(bytesOut);
copy(in, out);
return bytesOut.toByteArray();

更新2:真正的问题似乎是如何复制文件而不首先将其全部读入内存:

1)手动:

    byte[] buff = new byte[64*1024]; //or some size, can try out different sizes for performance
    BufferedInputStream in = new BufferedInputStream(new FileInputStream("fromFile"));
    BufferedOutputStream out = new BufferedOutputStream(new FileoutputStream("toFile"));
    int n = 0;
    while ((n = in.read(buff)) >= 0) {
        out.write(buff, 0, n);
    }
    in.close();
    out.close();

2)OS有效且无循环等:

FileChannel from = new FileInputStream(sourceFile).getChannel();
FileChanngel to = new FileOutputStream(destFile).getChannel();
to.transferFrom(from, 0, from.size());
//or from.transferTo(0, from.size(), to);
from.close();
to.close();

3)如果你有Java 7,你可以简化异常和流关闭,或者只使用java 7中的新API复制文件:

java.nio.file.Files.copy(...);

请参阅java.nio.file.Files