我有一个问题，这个方法应该使用流复制文件:
public static void copyFile() {
String[] paths = readSrcDestFromConsole(); //returns String array with two strings - source and destination file paths
InputStream is = null; OutputStream os = null;
File src = null; File dest = null;
boolean error = false;
long elapsedTimeSeconds = 0;
double speed = 0;
try {
src = new File(paths[0]);
}catch(Exception ex){
System.err.println("File read from could not be opened.");
error = true;
}
if(!error) {
try {
dest = new File(paths[1]);
}catch(Exception ex){
System.err.println("File written to could not be created.");
error = true;
}
if(src.exists() && !error) {
if(dest.exists()) {
System.out.println("File specified already exists. Do you want to overwrite it?");
if(askForOverwrite()) { // gets Y or N from console using scanner and returns a boolean
try {
is = new FileInputStream(src);
os = new FileOutputStream(dest);
System.out.println("Copying from: " + paths[0] + " to: " + paths[1]);
byte[] buffer = new byte[4096];
double read = 0;
long first = 0;
long second = 0;
long startTime = System.nanoTime();
while(is.read(buffer) > 0) {
read += buffer.length;
os.write(buffer);
first = Math.round(read / src.length() * 100);
if(first != second) {
System.out.println(first + " % copied.");
}
second = Math.round(read / src.length() * 100);
}
elapsedTimeSeconds = (System.nanoTime() - startTime) / 1_000_000_000;
speed = (src.length() / 1024 / 1024) / elapsedTimeSeconds;
is.close(); os.close();
}catch(Exception ex){
System.err.println("File is or has been corrupted.");
error = true;
}finally{
if(!error) {
if(src.length() == dest.length()) {
System.out.println("File copied successfully.");
System.out.println("Total size copied: " + ((dest.length()) / 1024 / 1024) + " MB");
System.out.println("Copying speed: " + speed + " MB/s" + " in " + elapsedTimeSeconds + " seconds.");
}else{
System.err.println("Error: " + "File sizes mismatch.");
}
}
}
}else{
System.out.println("File has not been rewritten.");
}
}else{
try {
is = new FileInputStream(src);
os = new FileOutputStream(dest);
System.out.println("Copying from: " + paths[0] + " to: " + paths[1]);
byte[] buffer = new byte[4096];
double read = 0;
long first = 0;
long second = 0;
long startTime = System.nanoTime();
while(is.read(buffer) > 0) {
read += buffer.length;
os.write(buffer);
first = Math.round(read / src.length() * 100);
if(first != second) {
System.out.println(first + " % copied.");
}
second = Math.round(read / src.length() * 100);
}
elapsedTimeSeconds = (System.nanoTime() - startTime) / 1_000_000_000;
speed = (src.length() / 1024 / 1024) / elapsedTimeSeconds;
is.close(); os.close();
}catch(Exception ex){
System.err.println("File is or has been corrupted.");
error = true;
}finally{
if(!error) {
if(src.length() == dest.length()) {
System.out.println("File copied successfully.");
System.out.println("Total size copied: " + ((dest.length()) / 1024 / 1024) + " MB");
System.out.println("Copying speed: " + speed + " MB/s" + " in " + elapsedTimeSeconds + " seconds.");
}else{
System.err.println("Error: " + "File sizes mismatch.");
}
}
}
}
}else{
System.err.println("File specified does not exist.");
}
}else{
System.err.println("Operation could not be completed.");
}
}
问题发生时，例如复制图像，文本文件或有时视频文件，错误"文件大小不匹配"发生。当我比较源文件和目标文件的大小时，大小确实不匹配，但打开后的图像似乎是完整的，视频也是如此。可见的问题是文本文件-在复制和丢失几个字节后，没有内容丢失，但在文件的末尾有几行带有某种标记的"NUL"-使用notepad++查看这些。
我尝试使用文件中的copy()方法，它可以正常工作，但我找不到为什么我的方法会丢失字节。
非常感谢你的帮助，我到处都找不到解决办法。
读循环是问题所在:
while(is.read(buffer) > 0) {
read += buffer.length;
os.write(buffer);
first = Math.round(read / src.length() * 100);
if(first != second) {
System.out.println(first + " % copied.");
}
second = Math.round(read / src.length() * 100);
}
is.read(buffer)返回读取的字节数。首先，你必须检查它是否大于或等于0，因为read的契约允许它读取0字节，如果缓冲区的大小为0。但除此之外，你需要保持这个值，因为你只需要写你读的字节数。
通常，文件的大小不是4096的整数倍。因此，最后一次读取将读取少于4096字节。read合约实际上说，即使在此之前，如果可用字节较少，它也可以读取少于4096的数据。
因此，如果你没有完全写入你所读的内容，那么你所写的缓冲区的一部分将包含前一次读取的值，如果文件小于4096字节，则为零。
所以更正为:
int numRead;
while( (numRead = is.read(buffer)) >= 0) {
read += numRead;
os.write(buffer,0,numRead);
first = Math.round(read / src.length() * 100);
if(first != second) {
System.out.println(first + " % copied.");
}
second = Math.round(read / src.length() * 100);
}
但是，实际上，每当您的副本涉及至少一个文件时，建议使用Files类，并且避免使用java.io.File而使用Path，并在Paths和Files中提供操作。