PushbackInputStream:回推缓冲区已满

Question

为什么我收到以下异常:

Exception in thread "main" java.io.IOException: Push back buffer is full
    at java.io.PushbackInputStream.unread(PushbackInputStream.java:232)
    at java.io.PushbackInputStream.unread(PushbackInputStream.java:252)
    at org.tests.io.PushBackStream_FUN.read(PushBackStream_FUN.java:32)
    at org.tests.io.PushBackStream_FUN.main(PushBackStream_FUN.java:43)

在这段代码中:

public class PushBackStream_FUN {
    public int write(String outFile) throws Exception {
        FileOutputStream outputStream = new FileOutputStream(new File(outFile));
        String str = new String("Hello World");
        byte[] data = str.getBytes();
        outputStream.write(data);
        outputStream.close();

        return data.length;
    }

    public void read(String inFile, int ln) throws Exception {
        PushbackInputStream inputStream = new PushbackInputStream(new FileInputStream(new File(inFile)));
        byte[] data = new byte[ln];
        String str;

        // read
        inputStream.read(data);
        str = new String(data);
        System.out.println("MSG_0 = "+str);
        // unread
        inputStream.unread(data);
        // read
        inputStream.read(data);
        str = new String(data);
        System.out.println("MSG_1 = "+str);
    }

    public static void main(final String[] args) throws Exception {
        PushBackStream_FUN fun = new PushBackStream_FUN();
        String path = "aome/path/output_PushBack_FUN";
        int ln = fun.write(path);
        fun.read(path, ln);
    }
}

UPDATE

认为这是解决方案.Java来源救援.我做了一些"实验".事实证明,当我使用PushbackInputStream指定的缓冲区大小指定时,它可以工作.java来源告诉我这个:

public PushbackInputStream(InputStream in) {
        this(in, 1);
    }

public PushbackInputStream(InputStream in, int size) {
        super(in);
        if (size <= 0) {
            throw new IllegalArgumentException("size <= 0");
        }
        this.buf = new byte[size];
        this.pos = size;
    }

我认为如果你使用PushbackInputStream使用默认缓冲区大小的constrcutor,你只能读取单字节.我读取超过单个字节,因此异常.

Answer 1

默认情况下,PushbackInputStream仅为unread()单个字符分配足够的空间.如果您希望能够推回更多,则必须在施工时指定容量.

在你的情况下,它看起来像这样:

final PushbackInputStream pis = new PushbackInputStream( inputStream, ln );