Question

由于某种原因无法删除和替换文件。

我只想从文件中删除1行。我找到了一种方法，方法是创建一个临时文件，然后逐个写入原始文件中的每一行，但要删除的行除外，然后用临时文件替换原始文件，但是尽管创建了临时文件，但原始文件却无法由于某种原因被删除和替换。我检查了文件未打开。

static final class PositionPriceWrapperBuilder extends RichCoFlatMapFunction<Position, Price, PositionPriceWrapper> {



    private transient MapState<String, Price>  priceState;
    private transient MapState<String, Position>  positionState;        

    @Override
    public void open(Configuration parameters) throws Exception {


        MapStateDescriptor<String, Price>  descPrice = new MapStateDescriptor<String, Price>(
                "priceState",
                String.class,
                Price.class);           
        priceState = getRuntimeContext().getMapState(descPrice);                
        System.out.println("descPrice:: " + descPrice);
        //Same thing needs to be done for Price?


        MapStateDescriptor<String, Position>  descPos = new MapStateDescriptor<String, Position>(
                "positionState",
                String.class,
                Position.class);            
        positionState = getRuntimeContext().getMapState(descPos);               
        System.out.println("positionState:: " + positionState);

    }           

    /**
     * 
     */
    private static final long serialVersionUID = 1L;

    @Override
    public void flatMap1(Position position, Collector<PositionPriceWrapper> out) throws Exception {
          try {
              //= pnlState.get(position.getId());
              Price price = priceState.get(position.getId());
              PositionPriceWrapper ppw = new PositionPriceWrapper();
              ppw.setPrice(price);
              ppw.setPosition(position);
              ppw.setAccount(position.getAccount());
              ppw.setCusip(position.getCusip());

              System.out.println("Built ppw -->" + ppw);

              positionState.put(position.getId(), position);
              out.collect(ppw);
          }
          catch ( Exception e) {
              e.printStackTrace();
          }

    }

    @Override
    public void flatMap2(Price price, Collector<PositionPriceWrapper> out) throws Exception {
          try {
              Position position = positionState.get(price.getId());
              PositionPriceWrapper ppw = new PositionPriceWrapper();
              ppw.setPrice(price);
              ppw.setPosition(position);
              ppw.setAccount(price.getAccount());
              ppw.setCusip(price.getCusip());

              priceState.put(price.getId(), price);
              out.collect(ppw);
          }
          catch ( Exception e) {
              e.printStackTrace();
          }         

    }

}

Answer 1

强烈建议使用java.nio.file.Files#delete(Path)方法而不是File#delete。阅读相关的question。此外，您不必删除文件并写入临时文件。只需阅读文本，根据需要对其进行过滤，最后从头开始重新编写相同的文件即可。（当然，写操作必须先关闭。）

看看这个例子：

public class ReadWrite {
    public static void main(String[] args) {
        File desktop = new File(System.getProperty("user.home"), "Desktop");
        File txtFile = new File(desktop, "hello.txt");
        StringBuilder sb = new StringBuilder();
        try (BufferedReader br = new BufferedReader(new FileReader(txtFile))) {
            String line;
            while ((line = br.readLine()) != null) {
                if ("this should not be read".equals(line))
                    continue;
                sb.append(line);
                sb.append(System.lineSeparator());
            }
        } catch (IOException e) {
            System.err.println("Error reading file.");
            e.printStackTrace();
        }

        try (PrintWriter out = new PrintWriter(txtFile)) {
            out.write(sb.toString());
        } catch (IOException e) {
            System.err.println("Error writing to file.");
            e.printStackTrace();
        }
    }
}

hello.txt初始内容：

hello there
stackoverflow
this should not be read
but what if it does?
then my answer
is going to get downvotes

运行后：

hello there
stackoverflow
but what if it does?
then my answer
is going to get downvotes

PS ：如果您使用的是Java 8+，请查看try-with resources和AutoClosable.

无法删除Java中的文件

1 个答案: