扩展 InputStreamReader 无法正常工作

Question

我这样扩展 InputStreamReader

public class AsteriskInputStreamReader extends InputStreamReader {
    boolean ast;
    AsteriskInputStreamReader(InputStream is) {
        super(is);
    }
    @Override
    public int read() throws IOException {
        ast = !ast;
        if (ast) return '*';
        return super.read();
    }
}

它必须在从原始 InputStream 获得的每个符号后添加 '*' 符号。但是当我这样使用它时

InputStreamReader in = new AsteriskInputStreamReader(new FileInputStream("text.txt"));
int c;
while((c = in.read()) != -1){
     System.out.print((char)c);
}

仅在文件中的最后一行 下才能正常工作。前几行仅输出为一个“*”，没有任何文本。为什么？

还有第二个问题。

当我用它创建 BufferedInputStream 并尝试获取文件的第一行时

BufferedReader reader = new BufferedReader(in);
System.out.println(reader.readLine());

我得到文件的第一行没有任何'*'。

获得我想要的内容的正确方法是什么：为 InputStreamReader 创建包装器，它将在原始输入的所有符号后添加星号？

Answer 1

第一部分的答案似乎是您正在写出回车符-return 字符。尝试通过将 System.out.print((char)c); 行替换为

来从输出中跳过它们

if (c != '\r') {
    System.out.print((char) c);
}

对于第二部分，您还需要在 AsteriskInputStreamReader class.

中覆盖 InputStreamReader 方法 read(char[] cbuf, int offset, int length)

Answer 2

而不是子类化 InputStreamReader, create a separate Reader that you can chain with other readers, so you can also apply it to readers that are not backed by InputStream。

try (BufferedReader reader = new BufferedReader(
                                new AsteriskReader(
                                   new InputStreamReader(
                                      new FileInputStream("text.txt"))))) {
    // ...
}

^{格式化以强调链。}

它不适用于 BufferedReader is that it doesn't call the read() method that you overwrote, it calls one of the overloads that takes a buffer (read(char[] cbuf), read(char[] cbuf, int off, int len), or read(CharBuffer target)) 的原因。

要实现要链接的 Reader，子类 FilterReader。

class AsteriskReader extends FilterReader {
    private boolean ast;
    private boolean astMarked;

    public AsteriskReader(Reader in) {
        super(in);
    }

    @Override
    public int read() throws IOException {
        // TODO Add handling of EOF
        ast = !ast;
        if (ast) return '*';
        return super.read();
    }

    @Override
    public int read(char[] cbuf, int off, int len) throws IOException {
        // TODO Implement this, i.e. only read half number of characters from
        //      underlying reader, then inject '*' characters between all the
        //      chars actually read.
        //      Special handling for odd value of len.
        int charsRead = super.read(cbuf, off, len);
        return charsRead;
    }

    @Override
    public long skip(long n) throws IOException {
        // TODO Fix this to handle odd value of n.
        long actualSkipped = super.skip(n / 2);
        return actualSkipped * 2;
    }

    @Override
    public void mark(int readAheadLimit) throws IOException {
        super.mark((readAheadLimit + 1) / 2); // Underlying reader only needs to remember half
        this.astMarked = this.ast;
    }

    @Override
    public void reset() throws IOException {
        super.reset();
        this.ast = this.astMarked;
    }

}

扩展 InputStreamReader 无法正常工作

Extending InputStreamReader does not work correctly

java

io