使用固定字节数java读取文件
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Reading a file using fixed number of bytes java
我正在编写一个程序来复制大文件，所以我想读取特定数量的字节并写入另一个文件。我想复制文件并获得相同的字节数。但我越来越多了。另外，我还希望文件的内容保持不变。我在这里做错了什么？如果有人能解释为什么我会收到这个额外的文字，那就太好了。
test.txt
sometext sometext sometext sometext
sometext sometext sometext sometext
sometext sometext sometext sometext
sometext sometext sometext sometext
public class Practice{
public static void main(String[] args){
byte[] buffer = new byte[100];
try{
FileInputStream f = new FileInputStream("test.txt");
FileWriter writer = new FileWriter("copy_test.txt");
int b;
while ((b=f.read(buffer)) != -1 )
writer.write(new String(buffer));
writer.close();
} catch(Exception e){
e.printStackTrace();
}
}
}
sometext sometext sometext sometext
sometext sometext sometext sometext
sometext sometext sometext sometext
sometext sometext sometext sometext
metext sometext sometext
sometext sometext sometext
byte[] buffer = new byte[1024];
int bytesRead;
while ((bytesRead = input.read(buffer)) != -1) {
output.write(buffer, 0, bytesRead);
}实践.java
sometext sometext sometext sometext
sometext sometext sometext sometext
sometext sometext sometext sometext
sometext sometext sometext sometext
public class Practice{
public static void main(String[] args){
byte[] buffer = new byte[100];
try{
FileInputStream f = new FileInputStream("test.txt");
FileWriter writer = new FileWriter("copy_test.txt");
int b;
while ((b=f.read(buffer)) != -1 )
writer.write(new String(buffer));
writer.close();
} catch(Exception e){
e.printStackTrace();
}
}
}
sometext sometext sometext sometext
sometext sometext sometext sometext
sometext sometext sometext sometext
sometext sometext sometext sometext
metext sometext sometext
sometext sometext sometext
byte[] buffer = new byte[1024];
int bytesRead;
while ((bytesRead = input.read(buffer)) != -1) {
output.write(buffer, 0, bytesRead);
}copy_test.txt
sometext sometext sometext sometext
sometext sometext sometext sometext
sometext sometext sometext sometext
sometext sometext sometext sometext
public class Practice{
public static void main(String[] args){
byte[] buffer = new byte[100];
try{
FileInputStream f = new FileInputStream("test.txt");
FileWriter writer = new FileWriter("copy_test.txt");
int b;
while ((b=f.read(buffer)) != -1 )
writer.write(new String(buffer));
writer.close();
} catch(Exception e){
e.printStackTrace();
}
}
}
sometext sometext sometext sometext
sometext sometext sometext sometext
sometext sometext sometext sometext
sometext sometext sometext sometext
metext sometext sometext
sometext sometext sometext
byte[] buffer = new byte[1024];
int bytesRead;
while ((bytesRead = input.read(buffer)) != -1) {
output.write(buffer, 0, bytesRead);
}您的代码有几个问题：
- 您正在使用默认平台编码将二进制数据转换为文本(通过调用 new String(byte[]) 而不是指定编码
- 您正在使用默认平台编码将文本写入磁盘(使用 FileWriter)
- 您无条件地将整个缓冲区转换为文本，即使您的读取没有填充它 - 您可以通过使用 String 构造函数重载之一来解决这个问题，该重载采用偏移量和字节数，并传递 0和 b 用于参数，尽管我不会。使用 try-with-resources 语句。
- 您根本没有关闭输入流，如果抛出异常，您也没有关闭编写器。使用 try-with-resources 语句。
- 您正在捕获 Exception - 这通常是个坏主意。如果必须，捕获特定异常；就我个人而言，我只有很少的 catch 块 - 通常如果出现问题，则中止整个当前操作是合适的。 (当然，在某些情况下您可以重试等。)我知道这可能只是在您的示例代码中，而不是在您的真实代码中。
- 如果您只是尝试复制文件，则根本没有理由在二进制和文本之间进行转换 - 坚持使用输入流和输出流
- 如果你只是想复制一个文件，你可以使用 Files.copy 来避免编写任何代码，假设你使用的是 Java 7。(如果你不是，你应该是！)
如果您只想将 InputStream 复制到 OutputStream (并且您没有可用的实用程序库 - 这是许多库的一部分)，您可以使用类似：
sometext sometext sometext sometext
sometext sometext sometext sometext
sometext sometext sometext sometext
sometext sometext sometext sometext
public class Practice{
public static void main(String[] args){
byte[] buffer = new byte[100];
try{
FileInputStream f = new FileInputStream("test.txt");
FileWriter writer = new FileWriter("copy_test.txt");
int b;
while ((b=f.read(buffer)) != -1 )
writer.write(new String(buffer));
writer.close();
} catch(Exception e){
e.printStackTrace();
}
}
}
sometext sometext sometext sometext
sometext sometext sometext sometext
sometext sometext sometext sometext
sometext sometext sometext sometext
metext sometext sometext
sometext sometext sometext
byte[] buffer = new byte[1024];
int bytesRead;
while ((bytesRead = input.read(buffer)) != -1) {
output.write(buffer, 0, bytesRead);
}