Spring boot 使用Filter

Filter 过滤器，可以对web请求进行相应的过滤，通过filter技术，对web服务器管理的所有web资源进行管理
实现原理
Filter接口中doFilter方法，配置服务器每次在调用web资源的service方法之前都会先调用filter的doFilter方法，可以在doFilter方法中编写代码，做相应的过滤，
可以控制的行为包括：
1、判断是否允许请求
2、是否允许访问目标资源
3、修改报文

举例 修改response报文内容

自定义过滤器 LoginFilter Response代理类 WrapperResponse
LoginFilter 类

       @WebFilter(urlPatterns = "/login", filterName = "loginFilter")
public class LoginFilter implements Filter {
    private final Logger log = LoggerFactory.getLogger(getClass());
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
        throws IOException, ServletException {
            ResponseWrapper wrapperResponse = new ResponseWrapper((HttpServletResponse) response);

    System.out.println("do filter");
    HttpServletRequest req = (HttpServletRequest) request;
    System.out.println(req.getRequestURI());
    Map<String, String[]> map = req.getParameterMap();
    System.out.println(req.getParameter("name"));
    if (map.containsKey("name") && map.get("name")[0].equals("1")) {
        chain.doFilter(request, wrapperResponse);

    } else {
        req.getRequestDispatcher("/failed").forward(request, wrapperResponse);
    }

    byte[] content = wrapperResponse.getResponseData();
    String str = new String(content)+"test";
    System.out.println("filter:" + str);
    HttpServletResponse res = (HttpServletResponse) response;
    writeResponse(res, 200, str);

    log.info("filter complete");

}

private void writeResponse(HttpServletResponse response, int status, String json) {
    try {
        response.reset();// 重置输入流
        response.setHeader("Access-Control-Allow-Origin", "*");
        response.setHeader("Access-Control-Allow-Methods", "*");
        response.setContentType("application/json;charset=UTF-8");
        response.setStatus(status);
        response.getWriter().write(json);
    } catch (IOException e) {
        e.printStackTrace();
    }

}

}

WrapperResponse 类

public class ResponseWrapper extends HttpServletResponseWrapper {
private ByteArrayOutputStream buffer = null;
private ServletOutputStream out = null;
private PrintWriter writer = null;

public ResponseWrapper(HttpServletResponse resp) throws IOException {
    super(resp);
    buffer = new ByteArrayOutputStream();// 数据流
    out = new WapperedOutputStream(buffer);
    writer = new PrintWriter(new OutputStreamWriter(buffer));
}

@Override
public ServletOutputStream getOutputStream() throws IOException {
    return out;
}

@Override
public PrintWriter getWriter() throws UnsupportedEncodingException {
    return writer;
}

@Override
public void flushBuffer() throws IOException {
    if (out != null) {
        out.flush();
    }
    if (writer != null) {
        writer.flush();
    }
}



public byte[] getResponseData() throws IOException {
    flushBuffer();
    return buffer.toByteArray();
}

public String getContent() throws IOException {
    flushBuffer();
    return buffer.toString();
}


private class WapperedOutputStream extends ServletOutputStream {
    private ByteArrayOutputStream bos = null;

    public WapperedOutputStream(ByteArrayOutputStream stream) throws IOException {
        bos = stream;
    }

    @Override
    public void write(int b) throws IOException {
        bos.write(b);
    }

    @Override
    public void write(byte[] b) throws IOException {
        bos.write(b, 0, b.length);
    }

    @Override
    public void write(byte[] b, int off, int len) throws IOException {
        bos.write(b, off, len);
    }

    @Override
    public boolean isReady() {
        return false;
    }

    @Override
    public void setWriteListener(WriteListener writeListener) {

    }
  }
}

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