本文主要是介绍Jsp/Servlet Request getReader()/getInputStream()返回空值的解决方法，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
因为同一次递交，request的三个方法getInputStream()/getReader()和getParameterMap()，任何一个方法使用过一次，postdata就会被清空,这三个方法再也无法使用。
现在有一个框架的流程是先用了getParameterMap()取出参数表，后面再视情况而定调用getreader()获得post data的具体数据， 如果用原来的request则无法满足此要求 ， 这时候我们可以自定义HttpServletRequestWrapper，在filter里面拦截处理。
首先，我们定义一个可复用post data的HttpServletRequestWrapper，里面有个rebuildParams()方法，用于将POST过来的带?key1=value1&key2=value2的url参数和post data好里面的参数合并在一起， 几个getXXX获取参数的都重写了，改为从合并后的参数列表中取出参数：
package com.freestyle.common.servletsupport;import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.net.URLDecoder;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Vector;import javax.servlet.ReadListener;
import javax.servlet.ServletInputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;import org.apache.commons.io.IOUtils;public class MultiReadHttpServletRequest extends HttpServletRequestWrapper {private ByteArrayOutputStream cachedBytes;private Map<String,String[]> mParams=null;public MultiReadHttpServletRequest(HttpServletRequest request) {super(request);}public void rebuildParams(){mParams=new HashMap<String,String[]>();String lvTmp=(String) getAttribute("_request_body");if (lvTmp!=null){ String[] lvItems=lvTmp.split("&");for(String item:lvItems){String[] lvItems1=item.split("=", 2);try {if (lvItems1.length==2){lvItems1[1]=URLDecoder.decode(lvItems1[1], "utf8");}} catch (UnsupportedEncodingException e) {// TODO Auto-generated catch blocke.printStackTrace();}if (mParams.containsKey(lvItems1[0])){String[] lvV=mParams.get(lvItems1[0]);List<String> lvList=new ArrayList<String>(Arrays.asList(lvV));if (lvItems1.length==2){lvList.add(lvItems1[1]);}else{lvList.add(null);}mParams.put(lvItems1[0], lvList.toArray(new String[lvList.size()]));}else{String[] lvV=new String[]{lvItems1.length==2? lvItems1[1]:null};mParams.put(lvItems1[0], lvV);} }}Map<String,String[]> lvParams=super.getParameterMap();for(java.util.Map.Entry<String, String[]> item:lvParams.entrySet()){mParams.put(item.getKey(),item.getValue());}}@Overridepublic ServletInputStream getInputStream() throws IOException {if (cachedBytes == null){cacheInputStream();}return new CachedServletInputStream();}public String getParameter(String pvKey){/*if (super.getParameterMap().containsKey(pvKey)){return super.getParameter(pvKey);}String[] lvRet=mParams.get(pvKey);if (lvRet==null)return null;return lvRet[0];*/Object lvV = mParams.get(pvKey); if (lvV == null) { return null; } else if (lvV instanceof String[]) { String[] lvStrArr = (String[]) lvV; if (lvStrArr.length > 0) { return lvStrArr[0]; } else { return null; } } else if (lvV instanceof String) { return (String) lvV; } else { return lvV.toString(); } }public Map<String, String[]> getParameterMap(){/*Map<String, String[]> lvRet=super.getParameterMap();lvRet.putAll(mParams);return lvRet;*/ return mParams;}public Enumeration getParameterNames() { Vector l = new Vector(mParams.keySet()); return l.elements(); } public String[] getParameterValues(String name) { Object v = mParams.get(name); if (v == null) { return null; } else if (v instanceof String[]) { return (String[]) v; } else if (v instanceof String) { return new String[] { (String) v }; } else { return new String[] { v.toString() }; } } @Overridepublic BufferedReader getReader() throws IOException{return new BufferedReader(new InputStreamReader(getInputStream()));}private void cacheInputStream() throws IOException {/* Cache the inputstream in order to read it multiple times. For* convenience, I use apache.commons IOUtils*/cachedBytes = new ByteArrayOutputStream();IOUtils.copy(super.getInputStream(), cachedBytes);}/* An inputstream which reads the cached request body */public class CachedServletInputStream extends ServletInputStream {private ByteArrayInputStream input;private boolean mIsFinished=false;public CachedServletInputStream() {/* create a new input stream from the cached request body */input = new ByteArrayInputStream(cachedBytes.toByteArray());mIsFinished=false;}@Overridepublic int read() throws IOException {int lvReaded=input.read();mIsFinished=lvReaded==-1;return lvReaded;}@Overridepublic boolean isFinished() {// TODO Auto-generated method stubreturn mIsFinished;}@Overridepublic boolean isReady() {// TODO Auto-generated method stubreturn false;}@Overridepublic void setReadListener(ReadListener arg0) {// TODO Auto-generated method stub}}}然后我们定义一个Filter， 重写doFilter方法，在里面重新定义request， 并在POST方法&非上传文件的时候将post Data放在“_request_body"属性里面， 后面框架里面有个通用类会从“_request_body”属性里面取出此post Data解析出相应的pojo类。
package com.freestyle.common.servletsupport;import java.io.IOException;import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;import org.apache.commons.fileupload.servlet.ServletFileUpload;import com.alco.bms.beans.HttpBeanUtil;public class RequestFilter implements Filter {@Overridepublic void doFilter(ServletRequest request, ServletResponse response,FilterChain chain) throws IOException, ServletException {/* wrap the request in order to read the inputstream multiple times */MultiReadHttpServletRequest multiReadRequest = new MultiReadHttpServletRequest((HttpServletRequest) request);/* here I read the inputstream and do my thing with it; when I pass the* wrapped request through the filter chain, the rest of the filters, and* request handlers may read the cached inputstream*/boolean isMultipart = ServletFileUpload.isMultipartContent(multiReadRequest);if (!isMultipart&&multiReadRequest.getMethod().toUpperCase().equals("POST")){String c_request_body=HttpBeanUtil.getRequestPayload(multiReadRequest);multiReadRequest.setAttribute("_request_body", c_request_body);}multiReadRequest.rebuildParams(); chain.doFilter(multiReadRequest, response);}@Overridepublic void destroy() {// TODO Auto-generated method stub}@Overridepublic void init(FilterConfig arg0) throws ServletException {// TODO Auto-generated method stubif (arg0==null){}}
}
而读出post data的方法很简单，如果用java 1.8的话，一句话就搞定了，下面写这么复杂只为了兼容性：
public static String getRequestPayload(HttpServletRequest req) {StringBuilder sb = new StringBuilder();try {BufferedReader reader = req.getReader();char[] buff = new char[1024];int len;while ((len = reader.read(buff)) != -1) {sb.append(buff, 0, len);}} catch (IOException e) {e.printStackTrace();}return sb.toString();}现在在web.xml里面增加此filter:
<filter><filter-name>MultiRequestCacheFilter</filter-name><filter-class>com.freestyle.common.servletsupport.RequestFilter</filter-class> </filter><filter-mapping><filter-name>MultiRequestCacheFilter</filter-name><url-pattern>*</url-pattern></filter-mapping>
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