Question

public FileProcessor(String filenameIn, String fileModeIn){
try {
     randomaccessfile = new RandomAccessFile(filenameIn, fileModeIn);
     fileChannel = randomaccessfile.getChannel();
     buffer = fileChannel.map(FileChannel.MapMode.READ_WRITE, 0, fileChannel.size());
} catch (FileNotFoundException e) {
    System.err.println("Error while creating a File");
    e.printStackTrace();
    System.exit(1);
} catch (IOException e) {
    System.err.println("Error while creating MappedByteBuffer");
    e.printStackTrace();
    System.exit(1);
}

获得

Exception in thread "main" java.nio.channels.NonWritableChannelException
at sun.nio.ch.FileChannelImpl.map(FileChannelImpl.java:880)

Answer 1

如果您在创建"rw"时需要RandomAccessFile映射文件时需要READ_WRITE，那么您最终会从中获取该文件。

Answer 2

当fileModeIn和FileChannel.MapMode.READ_WRITE没有匹配时，我的小型可重现程序会出现错误。

示例程序：

import java.io.*;
import java.nio.channels.*;
import java.nio.MappedByteBuffer;
class SampleFileProcessor {
    public static void main(String[] args) {
        String fileName = args[0];
        String mode = args[1];
        JFP jf = new JFP();
        jf.FileProcessor(fileName,mode);
    }

    public void FileProcessor(String filenameIn, String fileModeIn){
        try {
            RandomAccessFile randomaccessfile = new RandomAccessFile(filenameIn, fileModeIn);
            FileChannel fileChannel = randomaccessfile.getChannel();
            MappedByteBuffer buffer = fileChannel.map(FileChannel.MapMode.READ_WRITE, 0, fileChannel.size());
        } catch (FileNotFoundException e) {
            System.err.println("Error while creating a File");
            e.printStackTrace();
            System.exit(1);
        } catch (IOException e) {
            System.err.println("Error while creating MappedByteBuffer");
            e.printStackTrace();
            System.exit(1);
        } 
    }
}

输入＆amp;输出：

echo "Non-matching fileModeIn and FileChannel.MapMode"
java SampleFileProcessor input_file.txt r
Exception in thread "main" java.nio.channels.NonWritableChannelException
    at sun.nio.ch.FileChannelImpl.map(FileChannelImpl.java:799)
    at JFP.FileProcessor(JFP.java:19)
    at JFP.main(JFP.java:9)
<Error>

echo "Matching fileModeIn and FileChannel.MapMode"
java SampleFileProcessor input_file.txt rw
<Success>

JAVA - 不可写的通道异常

2 个答案: