Question

下载代码：

import java.io.*;

public class FileCharCopier
{
  public static void main(String args[]) throws IOException
  {

    File f1=new File("scjp.txt");
    File f2=new File("scjpcopy.txt");

    FileReader in=new FileReader(f1);
    FileWriter out=new FileWriter(f2);

    int c;

    while((c=in.read())!=1)
            {
      out.write(c);
      in.close();
      out.flush();
      out.close();


  }
}
}

我在同一目录中有scjp和scjpcopy.txt

但是当我运行程序时，我收到了这些错误：

java.io.IOException: Stream closed
    at sun.nio.cs.StreamEncoder.ensureOpen(Unknown Source)
    at sun.nio.cs.StreamEncoder.write(Unknown Source)
    at sun.nio.cs.StreamEncoder.write(Unknown Source)
    at java.io.OutputStreamWriter.write(Unknown Source)
    at FileCharCopier.main(FileCharCopier.java:18)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at edu.rice.cs.drjava.model.compiler.JavacCompiler.runCommand(JavacCompiler.java:272)

第18行指的是

out.write(c);

有人可以纠正错误吗？

Answer 1

基本上，您在while-loop的第一次迭代时关闭输入和输出流。这意味着当您尝试第二次循环时，流将被关闭并且它会抛出异常。

相反，您应该在完成后关闭流，例如。

public class FileCharCopier {

    public static void main(String args[]) throws IOException {

        File f1 = new File("scjp.txt");
        File f2 = new File("scjpcopy.txt");

        FileReader in = null;
        FileWriter out = null;

        try {

            in = new FileReader(f1);
            out = new FileWriter(f2);

            int c;

            while ((c = in.read()) != 1) {
                out.write(c);
            }

            out.flush();

        } finally {
            try {
                out.close();
            } catch (Exception e) {
            }
            try {
                in.close();
            } catch (Exception e) {
            }
        }
    }
}

这使用try-finally块来确保在循环存在或发生某些错误时，尽最大努力关闭流。

现在，如果您有幸使用Java 7，则可以改为使用try-with-resources语句，例如......

public class FileCharCopier {

    public static void main(String args[]) throws IOException {

        File f1 = new File("scjp.txt");
        File f2 = new File("scjpcopy.txt");

        try (FileReader in = new FileReader(f1); FileWriter out = new FileWriter(f2)) {

            int c;

            while ((c = in.read()) != 1) {
                out.write(c);
            }

            out.flush();

        } finally {
        }
    }
}

请查看The try-with-resources statement了解详情

Answer 2

从while循环中删除行in.close()和out.close()并将其设为：

while((c=in.read())!=1)
{
  out.write(c);
  out.flush();
}

它的作用：从文件中读取一个字符后，它会关闭阅读器，因此in不再附加输入文件并抛出异常。

参考this Oracle的文档。据说：
Closes the stream and releases any system resources associated with it. Once the stream has been closed, further read(), ready(), mark(), reset(), or skip() invocations will throw an IOException. Closing a previously closed stream has no effect.

Answer 3

将您的out.close();和in.close()放在while循环之外。

每次关闭输出流。写完所有内容之后，你可以在while循环之外关闭它。

希望有帮助。

Answer 4

您正在尝试写入它们时关闭流。将清理过程移出循环。

import java.io.*;
public class FileCharCopier
{
  //...same
    while((c=in.read())!=1){
          out.write(c);
          out.flush();
    }
          in.close();              
          out.close();
    }
}

这个FileWriter如何工作？

4 个答案: