文件拷貝

這個題目在筆試的時候常常出現，下面的代碼給出了兩種實現方案

 

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import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; import java.nio.ByteBuffer; import java.nio.channels.FileChannel;   public final class MyUtil {        private MyUtil() {          throw new AssertionError();      }        public static void fileCopy(String source, String target) throws IOException {          try (InputStream in = new FileInputStream(source)) {              try (OutputStream out = new FileOutputStream(target)) {                  byte [] buffer = new byte [ 4096 ];                  int bytesToRead;                  while ((bytesToRead = in.read(buffer)) != - 1 ) {                      out.write(buffer, 0 , bytesToRead);                  }              }          }      }        public static void fileCopyNIO(String source, String target) throws IOException {          try (FileInputStream in = new FileInputStream(source)) {              try (FileOutputStream out = new FileOutputStream(target)) {                  FileChannel inChannel = in.getChannel();                  FileChannel outChannel = out.getChannel();                  ByteBuffer buffer = ByteBuffer.allocate( 4096 );                  while (inChannel.read(buffer) != - 1 ) {                      buffer.flip();                      outChannel.write(buffer);                      buffer.clear();                  }              }          }      } }

 注意：上面用到Java 7的TWR，使用TWR後能夠不用在finally中釋放外部資源 ，從而讓代碼更加優雅。