如何从 servlet-filter 写入文件并在 Eclipse 中读取它？

Question

我想从我的过滤器写入一个文件，然后能够在 Eclipse 中读取它以确保我已正确写入它。

这段代码编译并运行良好，但我不知道我可以去哪里读取该文件，或者我是否写过任何东西。

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
    HttpServletRequest req = (HttpServletRequest) request;

    System.out.println("filter invoked");

    InputStream in = null;
    OutputStream out = null;
    String inPath = context.getRealPath("/WEB-INF/template.txt");
    String outPath = context.getRealPath("/WEB-INF/output.txt");
    in = new FileInputStream(inPath);
    out = new FileOutputStream(outPath);

    OutputStreamWriter outstream = new OutputStreamWriter(out);
    outstream.write("hello");


    // pass the request along the filter chain
    chain.doFilter(request, response);
}

文件 template.txt 和 output.txt 位于 WEB-INF 目录中。我已经验证从文件中读取工作正常，但我无法验证对它们的写入。每次我写入output.txt 时，该文件仍然没有更改。

关于在 Web 应用程序环境中写入文件，我不明白什么？

Answer 1

您必须关闭流（这也会刷新它）（在 finally 块中执行此操作）。顺便说一句，您可以使用 commons-io FileUtils 或 guava Files 这将使文件的处理变得更容易

但是，一般的做法并不是在webapp目录下写入文件，因为您将在下次重新部署时丢失它们。选择/配置外部位置来存储它们。

Answer 2

另外不要忘记将其包装到 try finally 块中。

OutputStreamWriter outstream = new OutputStreamWriter(out);
try {
    outstream.write("hello");
} finally {
    outstream.close();
}

Answer 3

您可以使用类似下面的内容，并让尝试使用资源来处理流。

@Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain chain)
            throws IOException, ServletException {
        // TODO Auto-generated method stub
        HttpServletRequest httpRequest = (HttpServletRequest) servletRequest;

        HttpServletResponse response = (HttpServletResponse) servletResponse;
        System.out.println(httpRequest.getRequestURI());
        System.out.println(httpRequest.getRequestURI().toLowerCase().endsWith("/v2/api-docs"));
        ByteArrayPrinter pw = new ByteArrayPrinter();
        // here i create a response wrapper
        HttpServletResponse wrappedResp = new HttpServletResponseWrapper(response) {
            @Override
            public PrintWriter getWriter() {
                return pw.getWriter();
            }

            @Override
            public ServletOutputStream getOutputStream() {
                return pw.getStream();
            }

        };
        System.out.println("before chaingin");
        // i get the response data from the stream
        chain.doFilter(httpRequest, wrappedResp);
        byte[] bytes = pw.toByteArray();
        String respBody = new String(bytes);
        System.out.println("in if" + respBody);
        if (httpRequest.getParameter("group") != null) {



            byte[] newByte = pw.toByteArray();
            String newString = new String(newByte);
            System.out.println("new string:" + newString);
            // i make a modification in the stream
            String s = newString.replaceAll("basePath", "Vijayy");
            System.out.println("printing s" + s);

            // here i try to write to a file with the modification
            try (FileOutputStream fos = new FileOutputStream(
                    new File(System.getProperty("user.dir") + "/static/openAPI.json"))) {
                System.out.println("comin in if");
                fos.write(s.getBytes());


                FileCopyUtils.copy(
                        new FileInputStream(new File(System.getProperty("user.dir") + "/static/openAPI.json")),
                        response.getOutputStream());

            } catch (FileNotFoundException ex) {
                ex.printStackTrace();
            }
            // FileCopyUtils.copy(, out);

            // IOUtils.copy(new ByteArrayInputStream(newString.getBytes()), response.getOutputStream());

        } else {
            chain.doFilter(httpRequest, wrappedResp);
            response.setHeader("Content-Type", MediaType.APPLICATION_JSON_VALUE);
            response.setContentLength(respBody.length());
            response.getOutputStream().write(respBody.getBytes());
        }

         return;
    }

ByteArrayprinter 是我为我的用例为 PrintStream 创建的包装器。同样，在您的情况下不需要考虑这一点