怎么构建可重复读取inputStream的request

本篇内容介绍了"怎么构建可重复读取inputStream的request"的有关知识，在实际案例的操作过程中，不少人都会遇到这样的困境，接下来就让小编带领大家学习一下如何处理这些情况吧！希望大家仔细阅读，能够学有所成！

构建可重复读取inputStream的request

我们知道，request的inputStream只能被读取一次，多次读取将报错，那么如何才能重复读取呢？答案之一是：增加缓冲，记录已读取的内容。

代码如下所示：

import lombok.extern.log4j.Log4j2;import org.springframework.mock.web.DelegatingServletInputStream;import javax.servlet.ServletInputStream;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletRequestWrapper;import java.io.*;/** * request wrapper: 可重复读取request.getInputStream */@Log4j2public class RepeatedlyReadRequestWrapper extends HttpServletRequestWrapper {    private static final int BUFFER_START_POSITION = 0;    private static final int CHAR_BUFFER_LENGTH = 1024;    /**     * input stream 的buffer     */    private final String body;    /**     * @param request {@link javax.servlet.http.HttpServletRequest} object.     */    public RepeatedlyReadRequestWrapper(HttpServletRequest request) {        super(request);        StringBuilder stringBuilder = new StringBuilder();        InputStream inputStream = null;        try {            inputStream = request.getInputStream();        } catch (IOException e) {            log.error("Error reading the request body…", e);        }        if (inputStream != null) {            try (BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream))) {                char[] charBuffer = new char[CHAR_BUFFER_LENGTH];                int bytesRead;                while ((bytesRead = bufferedReader.read(charBuffer)) > 0) {                    stringBuilder.append(charBuffer, BUFFER_START_POSITION, bytesRead);                }            } catch (IOException e) {                log.error("Fail to read input stream",e);            }        } else {            stringBuilder.append("");        }        body = stringBuilder.toString();    }    @Override    public ServletInputStream getInputStream() throws IOException {        final ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(body.getBytes());        return new DelegatingServletInputStream(byteArrayInputStream);    }}

接下来，需要一个对应的Filter.

代码如下所示：

import javax.servlet.*;import javax.servlet.http.HttpServletRequest;import java.io.IOException;public class RepeatlyReadFilter implements Filter {    @Override    public void init(FilterConfig filterConfig) throws ServletException {        //Do nothing    }    @Override    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {        if (request instanceof HttpServletRequest) {            request = new RepeatedlyReadRequestWrapper((HttpServletRequest) request);        }        chain.doFilter(request, response);    }    @Override    public void destroy() {        //Do nothing    }}

最后，需要在web.xml中，增加该Filter的配置（略）。

request中inputStream多次读取

在使用HTTP协议实现应用间接口通信时，服务端读取客户端请求过来的数据，会用到request.getInputStream()，第一次读取的时候可以读取到数据，但是接下来的读取操作都读取不到数据。

原因

一个InputStream对象在被读取完成后，将无法被再次读取，始终返回-1；

InputStream并没有实现reset方法（可以重置首次读取的位置），无法实现重置操作；

解决方法（缓存读取到的数据）

使用request、session等来缓存读取到的数据,这种方式很容易实现，只要setAttribute和getAttribute就行；

使用HttpServletRequestWrapper来包装HttpServletRequest，在中初始化读取request的InputStream数据，以byte[]形式缓存在其中，然后在Filter中将request转换为包装过的request；

代码

编写rHttpServletRequestWrapper子类，用来处理请求数据

import java.io.BufferedReader;import java.io.ByteArrayInputStream;import java.io.IOException;import java.io.InputStreamReader;import java.nio.charset.Charset;import java.util.Enumeration;import javax.servlet.ReadListener;import javax.servlet.ServletInputStream;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletRequestWrapper;import lombok.extern.slf4j.Slf4j;@Slf4jpublic class BodyReaderHttpServletRequestWrapper extends HttpServletRequestWrapper{        private final byte[] body;        public BodyReaderHttpServletRequestWrapper(HttpServletRequest request) throws IOException        {                super(request);                Enumeration e = request.getHeaderNames();                while (e.hasMoreElements())                {                        String name = (String) e.nextElement();                        String value = request.getHeader(name);                        log.debug("HttpServletRequest头信息：{}-{}", name, value);                }                body = HttpHelper.getBodyString(request).getBytes(Charset.forName("UTF-8"));        }        @Override        public BufferedReader getReader() throws IOException        {                return new BufferedReader(new InputStreamReader(getInputStream()));        }        @Override        public ServletInputStream getInputStream() throws IOException        {                final ByteArrayInputStream bais = new ByteArrayInputStream(body);                return new ServletInputStream(){                        @Override                        public boolean isFinished()                        {                                return false;                        }                        @Override                        public boolean isReady()                        {                                return false;                        }                        @Override                        public void setReadListener(ReadListener listener)                        {                                                        }                        @Override                        public int read() throws IOException                        {                                return bais.read();                        }                                        };                        }        @Override        public String getHeader(String name)        {                return super.getHeader(name);        }        @Override        public Enumeration getHeaderNames()        {                return super.getHeaderNames();        }        @Override        public Enumeration getHeaders(String name)        {                return super.getHeaders(name);        }}

调用

public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) throws IOException, ServletException        {                HttpServletRequest httpRequest = (HttpServletRequest) request;                HttpServletResponse httpResponse = (HttpServletResponse) response;                                ServletRequest requestWrapper = null;                requestWrapper = new BodyReaderHttpServletRequestWrapper(httpRequest);                                //数据读取处理                //...                //将requestWrapper专递给后面的过滤器                filterChain.doFilter(requestWrapper, httpResponse);        }

"怎么构建可重复读取inputStream的request"的内容就介绍到这里了，感谢大家的阅读。如果想了解更多行业相关的知识可以关注网站，小编将为大家输出更多高质量的实用文章！