解决request请求流中数据只能读取一次问题

实际开发中碰到的问题

公司内应用想使用平台功能时，需要先进行注册与配置，编写过滤器，过滤掉没有注册和配置的应用，如果应用注册并且配置则继续向下执行，但在后面的代码中想获取应用相关信息，发现request中body的内容为空

问题在于request的输入流只能读取一次不能重复读取，所以我们在过滤器器或拦截器里读取了request的输入流之后，请求走到controller层就会报错

HttpServletRequest的输入流只能读取一次的原因

当我们调用getInputStream()方法获取输入流时得到的是一个InputStream对象，而实际类型是ServletInputStream，它继承与InputStream。

InputStream的read()方法内部有一个position，标志当前流被读取到的位置，每读取一次，该标志就会移动一次，如果读到最后，read()返回-1，表示已经读取完了，如果想要重新读取，则需要调用reset()方法，position就会移动到上次调用mark的位置，mark默认是0，所有就能重头再读了。调用reset()方法的前提是已经重写了reset()方法，当然能否reset也是有条件的，它取决于markSupported()方法是否返回true。

InputStream默认不实现reset()，并且markSupported()默认也是返回false

	/**
     * Repositions this stream to the position at the time the
     * <code>mark</code> method was last called on this input stream.
     *
     * <p> The general contract of <code>reset</code> is:
     *
     * <ul>
     * <li> If the method <code>markSupported</code> returns
     * <code>true</code>, then:
     *
     *     <ul><li> If the method <code>mark</code> has not been called since
     *     the stream was created, or the number of bytes read from the stream
     *     since <code>mark</code> was last called is larger than the argument
     *     to <code>mark</code> at that last call, then an
     *     <code>IOException</code> might be thrown.
     *
     *     <li> If such an <code>IOException</code> is not thrown, then the
     *     stream is reset to a state such that all the bytes read since the
     *     most recent call to <code>mark</code> (or since the start of the
     *     file, if <code>mark</code> has not been called) will be resupplied
     *     to subsequent callers of the <code>read</code> method, followed by
     *     any bytes that otherwise would have been the next input data as of
     *     the time of the call to <code>reset</code>. </ul>
     *
     * <li> If the method <code>markSupported</code> returns
     * <code>false</code>, then:
     *
     *     <ul><li> The call to <code>reset</code> may throw an
     *     <code>IOException</code>.
     *
     *     <li> If an <code>IOException</code> is not thrown, then the stream
     *     is reset to a fixed state that depends on the particular type of the
     *     input stream and how it was created. The bytes that will be supplied
     *     to subsequent callers of the <code>read</code> method depend on the
     *     particular type of the input stream. </ul></ul>
     *
     * <p>The method <code>reset</code> for class <code>InputStream</code>
     * does nothing except throw an <code>IOException</code>.
     *
     * @exception  IOException  if this stream has not been marked or if the
     *               mark has been invalidated.
     * @see     java.io.InputStream#mark(int)
     * @see     java.io.IOException
     */
    public synchronized void reset() throws IOException {
        throw new IOException("mark/reset not supported");
    }

    /**
     * Tests if this input stream supports the <code>mark</code> and
     * <code>reset</code> methods. Whether or not <code>mark</code> and
     * <code>reset</code> are supported is an invariant property of a
     * particular input stream instance. The <code>markSupported</code> method
     * of <code>InputStream</code> returns <code>false</code>.
     *
     * @return  <code>true</code> if this stream instance supports the mark
     *          and reset methods; <code>false</code> otherwise.
     * @see     java.io.InputStream#mark(int)
     * @see     java.io.InputStream#reset()
     */
    public boolean markSupported() {
        return false;
    }

我们再来看看ServletInputStream，可以看到该类并没有重写mark(),reset()以及markSupported()方法

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package javax.servlet;

import java.io.IOException;
import java.io.InputStream;

/**
 * Provides an input stream for reading binary data from a client request,
 * including an efficient <code>readLine</code> method for reading data one line
 * at a time. With some protocols, such as HTTP POST and PUT, a
 * <code>ServletInputStream</code> object can be used to read data sent from the
 * client.
 * <p>
 * A <code>ServletInputStream</code> object is normally retrieved via the
 * {@link ServletRequest#getInputStream} method.
 * <p>
 * This is an abstract class that a servlet container implements. Subclasses of
 * this class must implement the <code>java.io.InputStream.read()</code> method.
 *
 * @see ServletRequest
 */
public abstract class ServletInputStream extends InputStream {

    /**
     * Does nothing, because this is an abstract class.
     */
    protected ServletInputStream() {
        // NOOP
    }

    /**
     * Reads the input stream, one line at a time. Starting at an offset, reads
     * bytes into an array, until it reads a certain number of bytes or reaches
     * a newline character, which it reads into the array as well.
     * <p>
     * This method returns -1 if it reaches the end of the input stream before
     * reading the maximum number of bytes.
     *
     * @param b
     *            an array of bytes into which data is read
     * @param off
     *            an integer specifying the character at which this method
     *            begins reading
     * @param len
     *            an integer specifying the maximum number of bytes to read
     * @return an integer specifying the actual number of bytes read, or -1 if
     *         the end of the stream is reached
     * @exception IOException
     *                if an input or output exception has occurred
     */
    public int readLine(byte[] b, int off, int len) throws IOException {

        if (len <= 0) {
            return 0;
        }
        int count = 0, c;

        while ((c = read()) != -1) {
            b[off++] = (byte) c;
            count++;
            if (c == '\n' || count == len) {
                break;
            }
        }
        return count > 0 ? count : -1;
    }

    /**
     * Has the end of this InputStream been reached?
     *
     * @return <code>true</code> if all the data has been read from the stream,
     * else <code>false</code>
     *
     * @since Servlet 3.1
     */
    public abstract boolean isFinished();

    /**
     * Can data be read from this InputStream without blocking?
     * Returns  If this method is called and returns false, the container will
     * invoke {@link ReadListener#onDataAvailable()} when data is available.
     *
     * @return <code>true</code> if data can be read without blocking, else
     * <code>false</code>
     *
     * @since Servlet 3.1
     */
    public abstract boolean isReady();

    /**
     * Sets the {@link ReadListener} for this {@link ServletInputStream} and
     * thereby switches to non-blocking IO. It is only valid to switch to
     * non-blocking IO within async processing or HTTP upgrade processing.
     *
     * @param listener  The non-blocking IO read listener
     *
     * @throws IllegalStateException    If this method is called if neither
     *                                  async nor HTTP upgrade is in progress or
     *                                  if the {@link ReadListener} has already
     *                                  been set
     * @throws NullPointerException     If listener is null
     *
     * @since Servlet 3.1
     */
    public abstract void setReadListener(ReadListener listener);
}

综上，InputStream默认不实现reset方法，而ServletInputStream也没有重写reset相关方法，这样就无法重复读取流，这就是我们从request对象中获取输入流就只能读取一次的原因

解决

我们可以把流读取出来后用容器存起来，后面就可以多次利用了。JavaEE提供了一个HttpServletRequestWrapper类，它是一个http请求包装器，基于装饰者模式实现类HttpServletRequest界面。

package javax.servlet.http;

import java.io.IOException;
import java.util.Collection;
import java.util.Enumeration;
import java.util.Map;

import javax.servlet.ServletException;
import javax.servlet.ServletRequestWrapper;

/**
 * Provides a convenient implementation of the HttpServletRequest interface that
 * can be subclassed by developers wishing to adapt the request to a Servlet.
 * This class implements the Wrapper or Decorator pattern. Methods default to
 * calling through to the wrapped request object.
 *
 * @see javax.servlet.http.HttpServletRequest
 * @since v 2.3
 */
public class HttpServletRequestWrapper extends ServletRequestWrapper implements
        HttpServletRequest {

    /**
     * Constructs a request object wrapping the given request.
     *
     * @param request The request to wrap
     *
     * @throws java.lang.IllegalArgumentException
     *             if the request is null
     */
    public HttpServletRequestWrapper(HttpServletRequest request) {
        super(request);
    }

    private HttpServletRequest _getHttpServletRequest() {
        return (HttpServletRequest) super.getRequest();
    }

    /**
     * The default behavior of this method is to return getAuthType() on the
     * wrapped request object.
     */
    @Override
    public String getAuthType() {
        return this._getHttpServletRequest().getAuthType();
    }

    /**
     * The default behavior of this method is to return getCookies() on the
     * wrapped request object.
     */
    @Override
    public Cookie[] getCookies() {
        return this._getHttpServletRequest().getCookies();
    }

从源码中可以看到，该类并没有真正去实现HttpServletRequest的方法，而只是在方法内又去调用HttpServletRequest的方法，所以我们可以通过继承该类并实现想要重新定义的方法达到包装原生HttpServletRequest的目的

继承HttpServletRequestWrapper，将请求体中的流copy一份，可以重写getinputStream()和getReader()方法，或自定义方法供外部使用。

public class MAPIHttpServletRequestWrapper extends HttpServletRequestWrapper {
    //存储body数据的容器
    private final byte[] body;
    
    public MAPIHttpServletRequestWrapper(HttpServletRequset request) throws IOException {
        super(request);
        //将body数据存起来
        InputStream is = request.getInputStream();
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        byte buff[] = new byte[1024];
        int len;
        while ((len = is.read(buff)) > 0) {
            baos.write(buff, 0, len);
        }
        body = baos.toByteArray();
    }
    
    /**
     * 将inputStream里的数据读取出来并转换成Map
     *
     * @param inputStream
     * @return Map<String,Object>
     */
    public static Map<String, Object> getBodyMap(InputStream in) {
        String param = null;
        BufferedReader streamReader = null;
        try {
            streamReader = new BufferReader(new InputStreamReader(in, "UTF-8"));
            StringBuilder responseStrBuilder = new StringBuilder();
            String inputStr;
            while ((inputStr = streamReader.readLine()) != null) {
            	responseStrBuilder.append(inputStr);
            }
            JSONObject jsonObject = JSONObject.parseObject(responseStrBuilder.toString());
            if (jsonObject == null) {
                return new HashMap<String,Object>();
            }
            param = jsonObject.toJSONString();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (streamReader != null){
                try {
                    streamReader.close();
                } catch (Exception e) {
           			 e.printStackTrace();
       			}
            }
        }
        return JSONObject.parseObject(param,Map.class);
    }
    
    @Override
    public BufferedReader getReader() throws IOException {
        return new BufferedReader(new InputStreamReader(getInputStream()));
    }

    @Override
    public ServletInputStream getInputStream() throws IOException {

        final ByteArrayInputStream inputStream = new ByteArrayInputStream(body);

        return new ServletInputStream() {
            @Override
            public int read() throws IOException {
                return inputStream.read();
            }

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

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

            @Override
            public void setReadListener(ReadListener readListener) {
            }
        };
    }
}

编写过滤器

@Slf4j
@WebFilter(filterName = "MyFilter", urlPattern = "/*")
public class MyFilter implements Filter {
//    @Autowired
//    @Qualifier("redisService")
//    private CeManager ceManager;
    
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        log.info("MyFilter初始化...");
    }
    
    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest req = (HttpServletRequest) servletRequest;
        HttpServletResponse res = (HttpServletResponse) servletResponse;
        ServletRequest requestWrapper = new MAPIHttpServletRequestWrapper(req);
        Map<String,Object> resultMap = MAPIHttpServletRequestWrapper.getBodyMap(requestWrapper.getInputStream());
       
        //业务逻辑
//        String key = (String) resultMap.get("key");
//        if (ceManager.exists(key)) {
//            filterChain.doFilter(requestWrapper, servletResponse);
//        }else {
//            responseData(servletResponse,res,"5001","应用未注册！")
//        }
    }
    
//    private void responseData(ServletResponse response, HttpServletResponse res, String code, String message) throws IOException {
//        response.setCharacterEncoding("UTF-8");
//        response.setContentType("application/json; charset=utf-8");
//        PrintWriter out = null;
//        try {
//            JSONObject obj = new JSONObject();
//            obj.put("code",code);
//            obj.put("message",message);
//            out = res.getWriter();
//            out.append(obj.toString);
//        } catch (Exception e) {
//            e.printStackTrace();
//            res.sendError(500);
//        } finally {
//            if (out != null){
//                out.close();
//            }
//        }
//    }
    
    @Override
    public void destroy() {
        log.info("MyFilter销毁...");
    }
	
}