java - 使用FileReader读取文件

Question

今天，我阅读了Java教程中的Basic I/O，发现了一些问题:

public class CopyCharacters {
    public static void main(String[] args) throws IOException {
        FileReader inputStream = null;
        FileWriter outputStream = null;
        try {
            inputStream = new FileReader("/workspaces/test/a.txt");
            outputStream = new FileWriter("/workspaces/test/b.txt");
            int c;
            while ((c = inputStream.read()) != -1) {
                outputStream.write(c);
            }
        } finally {
            if (inputStream != null) {
                inputStream.close();
            }
            if (outputStream != null) {
                outputStream.close();
            }
        }
    }
}

但是当我运行演示时，它失败了。在控制台中:

Exception in thread "main" java.io.FileNotFoundException: /workspaces/test/b.txt (Access is denied)
    at java.io.FileOutputStream.open(Native Method)
    at java.io.FileOutputStream.<init>(FileOutputStream.java:221)
    at java.io.FileOutputStream.<init>(FileOutputStream.java:110)
    at java.io.FileWriter.<init>(FileWriter.java:63)
    at Demo.CopyCharacters.main(CopyCharacters.java:13)

我怎样才能做到这一点？

Answer 1

文件可能有锁，并禁止您打开它进行写入(即您的应用程序仍处于 Debug模式下的断点，而您忘记停止它，或者您杀死了应用程序，但进程仍在内存中运行)。您可以通过执行以下操作进行检查:

        inputStream = new FileReader("/workspaces/test/a.txt");
        File outFile = new File("/workspaces/test/b.txt");
        if (!outFile.canWrite()) {
            System.err.println("Cannot write into file: " + outFile.getAbsolutePath());
        }
        outputStream = new FileWriter(outFile);

您还可以将输出文件“b.txt”重命名为其他名称，它将像以前一样工作(直到您意外再次锁定它)。另一种方法是使用临时文件:

    public static void main(String[] args) throws Exception {
    FileReader inputStream = null;
    FileWriter outputStream = null;
    try {
        inputStream = new FileReader("/workspaces/test/a.txt");
        File file = File.createTempFile("test", null);
        outputStream = new FileWriter(file);
        System.out.println(file.getAbsolutePath());
        int c;
        while ((c = inputStream.read()) != -1) {
            outputStream.write(c);
        }
    } finally {
        if (inputStream != null) {
            inputStream.close();
        }
        if (outputStream != null) {
            outputStream.close();
        }
    }

}

适合编码(和调试)。它确保之后它会被操作系统删除。