如何锁定Excel文件以在java中读写？

Question

I am reading a input channel using spring and whichever file comes in I am picking up the same. Basically the file is excel file hence I have used apache POI workbook . Below is the App class

@SpringBootConfiguration
@EnableScheduling
@Component
public class App
{
    public static void main( String[] args ) throws IOException
    {
         SpringApplication.run(App.class, args);
    }

    @Scheduled(fixedRate = 60000)
    public static void displayDirectories () throws InvalidFormatException, IOException{
        ApplicationContext context = new ClassPathXmlApplicationContext("context.xml", App.class);
        File inDir = (File) new DirectFieldAccessor(context.getBean(FileReadingMessageSource.class)).getPropertyValue("directory");
        LiteralExpression expression = (LiteralExpression) new DirectFieldAccessor(context.getBean(FileWritingMessageHandler.class)).getPropertyValue("destinationDirectoryExpression");
        File outDir = new File(expression.getValue());
        System.out.println("Input directory is: " + inDir.getAbsolutePath());
        System.out.println("Archive directory is: " + outDir.getAbsolutePath());
        System.out.println("===================================================");
    }
}

Below are some configurations from my bean context.xml:

<file:inbound-channel-adapter id="filesIn"
    directory="file:${java.io.tmpdir}/input">
    <integration:poller id="poller" fixed-rate="60000"/>
</file:inbound-channel-adapter>

<integration:service-activator
    input-channel="filesIn" output-channel="filesOut" ref="handler" />

<file:outbound-channel-adapter id="filesOut"
    directory="file:${java.io.tmpdir}/archive" delete-source-files="true">
</file:outbound-channel-adapter>

<bean id="handler" class="com.practice.Handler" />

Below is my handler class where I am trying to acquire lock on excel file read:

@SpringBootConfiguration
@Component
public class Handler {
    FileInputStream fileIn = null;
    FileLock lock = null;
    public File handleFile(File input) {
        try {
            fileIn = new FileInputStream(input);
            lock = fileIn.getChannel().tryLock();
            Workbook filename = WorkbookFactory.create(fileIn);
            .
            /*Some logic*/
            .
        }
        catch(Exception e){
            System.out.println("Exception occured");
            e.printStackTrace();
        }
        finally{
            try {
                lock.release();
                fileIn.close();
            } catch (IOException e) {
                System.out.println("Exception in fileclose or lock");
                e.printStackTrace();
            }
        }
        return input;
    }
}

Not implementing the lock reads my file multiple times and it process it multiple times. My assignment is to read the file once and process it and then archive the same. When I tried implementing lock in above code I am getting an exception java.nio.channels.NonWritableChannelException . However it is suggesting me to change the same to POIFSFileSystem to resolve the same. I tried the suggestions on google and they all are suggesting only for RandomAccessFile only. I am using spring boot for the project. Any help upon this would be much appreciated.

Answer 1

We can lock the file, read it, modify the sheet and write it, then release the lock. That is an important use case. Every spreadsheet program works like that.

Working test case With Apache POI 4.1.1:

public static void main(String[] args) throws Exception{
    File testFile = new File("src/main/resources/test.xls");
    if(! testFile.exists()){
        throw new FileNotFoundException(testFile.getAbsolutePath());
    }
    RandomAccessFile randomAccessFile = new RandomAccessFile(testFile, "rw");
    FileChannel fileChannel = randomAccessFile.getChannel();
    FileLock fileLock = fileChannel.tryLock();
    if(fileLock == null){
        throw new NullPointerException("Cannot get lock.");
    }
    boolean readOnly = false;
    POIFSFileSystem filesystem = new POIFSFileSystem(fileChannel, readOnly);
    HSSFWorkbook workbook = new HSSFWorkbook(filesystem);
    workbook.write();
    fileLock.release();
    workbook.close();
    if(!testFile.delete()){
        throw new RuntimeException("Could not delete test file.");
    }
}