java 底层流返回零字节
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Underlying stream returned zero bytes
提问by IchBinKeinBaum
I'm currently writing my own Brainfwor interpreter in Java and because I want it to be able to read code from files I wrote a BFInputStreamthat filters unnecessary symbols out. It looks like this:
我目前正在用 Java 编写自己的 Brainfwor 解释器，因为我希望它能够从文件中读取代码，所以我编写了一个BFInputStream过滤掉不必要符号的文件。它看起来像这样：
import java.io.FilterInputStream;
import java.io.InputStream;
import java.io.IOException;
public class BFInputStream extends FilterInputStream {
public BFInputStream(InputStream in) {
super(in);
}
public int read() throws IOException {
while(true) {
int i = super.read();
// keep LF for line number checking.
if(i == -1 || i == 10 ||( i >= 43 && i <= 46) || i == 60 || i == 62 || i == 91 || i == 93)
return i;
}
}
public int read(byte[] b, int off, int len) throws IOException {
if(off < 0 || len < 0 || len > b.length - off) throw new IndexOutOfBoundsException();
for(int i=0; i<len; i++) {
int j = read();
if(j < 1) return i;
b[off+i] = (byte)j;
}
return len;
}
}
My Interpreter uses LineNumberReader<-InputStreamReader<-BFInputStream<-FileInputStreamto read the file. But everytime it reaches the end of the file it throws:
我的解释器使用LineNumberReader<- InputStreamReader<- BFInputStream<-FileInputStream来读取文件。但每次到达文件末尾时，它都会抛出：
java.io.IOException: Underlying input stream returned zero bytes
at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:268) at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:306) at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:158) at java.io.InputStreamReader.read(InputStreamReader.java:167) at java.io.BufferedReader.fill(BufferedReader.java:136) at java.io.BufferedReader.read(BufferedReader.java:157) at java.io.LineNumberReader.read(LineNumberReader.java:108) at Interpreter.run(Interpreter.java:101) at Interpreter.main(Interpreter.java:180)
java.io.IOException：底层输入流返回零字节
at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:268) at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:306) at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:158) at java.io.InputStreamReader.read(InputStreamReader.java:167) at java.io.BufferedReader.fill(BufferedReader.java:136) at java.io.BufferedReader.read(BufferedReader.java:157) at java.io.LineNumberReader.read(LineNumberReader.java:108) at Interpreter.run(Interpreter.java:101) at Interpreter.main(Interpreter.java:180)
Interpreter.java:101 contains a call to BFInputStream.read().
Interpreter.java:101 包含对 的调用BFInputStream.read()。
I'm not sure if I understand the exception correctly. I think the stream returned no bytes at all (because of a timeout). I guess if there was a huge chunk of non-BF characters then that could be possible but at the end of the file? FileInputStreamand therefore FilterInputStreamand BFInputStreamshould return -1.
我不确定我是否正确理解异常。我认为流根本没有返回字节（因为超时）。我想如果有一大块非 BF 字符，那么这可能是可能的，但是在文件的末尾？FileInputStream因此FilterInputStream并且BFInputStream应该返回-1。
What is wrong with my code?
我的代码有什么问题？
回答by axtavt
if (j < 1)should be if (j < 0), because EOF is indicated by -1. Also, your method never returns -1 at EOF.
if (j < 1)应该是if (j < 0)，因为 EOF 由 表示-1。此外，您的方法永远不会在 EOF 返回 -1。
The correct implementation would look like this:
正确的实现如下所示：
public int read(byte[] b, int off, int len) throws IOException {
if(off < 0 || len <= 0 || len > b.length - off) throw new IndexOutOfBoundsException();
int i = 0;
while (i < len) {
int j = read();
if (j < 0) break; // Stop reading at EOF
b[off + i] = (byte) j;
i++;
}
if (i == 0) return -1; // If we get EOF with no data, return it to the caller
else return i;
}
回答by Kumar Vivek Mitra
Well did same kinda thing before but using File, FileReader/Writer and BufferReader/Writer. I am giving you the snippet of code i use as guidelines.. try it
之前也做过同样的事情，但使用 File、FileReader/Writer 和 BufferReader/Writer。我给你我用作指导的代码片段..试试看
For Reading from a file
用于从文件中读取
File f = new File("my.txt");
FileReader fr = new FileReader(f);
BufferedReader br = new BufferedReader(fr);
String s = null;
while ((br=readLine())!=null) {
// Do whatever u want to do with the content of the file.
}
br.close();
For Writing to a file:
写入文件：
Boolean isDone = true;
Scanner scan = new Scanner(System.in);
File f = new File("my.txt");
FileWriter fr = new FileWriter(f);
BufferedWriter br = new BufferedWriter(fr);
while (b) {
if (!b) {
br.write(new Scanner(System.in).nextLine());
}
}
