解決在Filter中讀取Request中的流後，後續controller或restful接口中無法獲取流的問題
首先我們來描述一下在開發中遇到的問題，場景如下：
比如我們要攔截所有請求，獲取請求中的某個參數，進行相應的邏輯處理：比如我要獲取所有請求中的公共參數 token,clientVersion等等；這個時候我們通常有兩種做法
前提條件是我們實現Filter類，重寫doFilter方法
1、通過getParameter方法獲得
HttpServletRequest hreq = (HttpServletRequest) req;
String param = hreq.getParameter("param");
這種方法有缺陷：它只能獲取 POST 提交方式中的
Content-Type: application/x-www-form-urlencoded;
這種提交方式中，key為param ,若提交類型不是這種方式就獲取不到param的值
2、獲取請求對象中的數據流，通過解析流信息來獲取提交的內容；代碼示例如下：
[java] view plain copy /**
* 獲取請求Body
*
* @param request
* @return
*/
public static String getBodyString(ServletRequest request) {
StringBuilder sb = new StringBuilder();
InputStream inputStream = null;
BufferedReader reader = null;
try {
inputStream = request.getInputStream();
reader = new BufferedReader(new InputStreamReader(inputStream, Charset.forName("UTF-8")));
String line = "";
while ((line = reader.readLine()) != null) {
sb.append(line);
}
} catch (IOException e) {
e.printStackTrace();
} finally {
if (inputStream != null) {
try {
inputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if (reader != null) {
try {
reader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
return sb.toString();
}
通過這種簡單的解析方式，將http請求中的body解析成 字符串的形式；然後再對字符串的格式進行業務解析；
這種處理方式的優點是：能解析 出content-Type 為 application/x-www-form-urlencoded ，application/json , text/xml 這三種提交方式的 數據 （至於另外一種帶文件的請求：multipart/form-data ，本人沒有親自測試過，等後期遇到此類為題再來解決）。 上述方法返回的可能是key,value(對應第一種content-type),可能是json字符串（對應第二種），可能是xml的字符串（對應第三種）
但是這種方式有一個很大的缺點：那就是當從請求中獲取流以後，流被filter中的這個 inputStreamToString(InputStream in) 這個方法處理後就被“消耗”了，這會導致，chain.doFilter(request, res)這個鏈在傳遞 request對象的時候，裏面的請求流為空，導致責任鏈模式下，其他下遊的鏈無法獲取請求的body,從而導致程序無法正常運行，這也使得我們的這個filter雖然可以獲取請求信息，但是它會導致整個應用程序不可用，那麽它也就失去了意義；
針對第二種方式的缺陷：流一旦被讀取，就無法向下傳遞整個問題，有如下解決方案；
解決思路如下：將取出來的字符串，再次轉換成流，然後把它放入到新request 對象中，在chain.doFiler方法中 傳遞新的request對象；要實現這種思路，需要自定義一個類
繼承HttpServletRequestWrapper，然後重寫public BufferedReader getReader()方法，public ServletInputStream getInputStream()方法；（這兩個方法的重寫實現邏輯如下：getInputStream（）方法中將body體中的字符串轉換為字節流（它實質上返回的是一個ServletInputStream 對象）；然後通過getReader()調用---->getInputStream（）方法；），繼承實現重寫邏輯以後，在自定義分filter（VersionCheckFilter）中，使用自定義的HttpServletRequestWrapper（BodyReaderHttpServletRequestWrapper）將原始的HttpServletRequest對象進行再次封裝；再通過BodyReaderHttpServletRequestWrapper對象去做dofilter(req,res)的req對象；
涉及的三個類的代碼如下：
自定義的HttpServletRequestWrapper
[java] view plain copyimport 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.ServletInputStream; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletRequestWrapper; import com.yt.util.HttpHelper; public class BodyReaderHttpServletRequestWrapper extends HttpServletRequestWrapper { private final byte[] body; public BodyReaderHttpServletRequestWrapper(HttpServletRequest request) throws IOException { super(request); System.out.println("-------------------------------------------------"); Enumeration e = request.getHeaderNames() ; while(e.hasMoreElements()){ String name = (String) e.nextElement(); String value = request.getHeader(name); System.out.println(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 int read() throws IOException { return bais.read(); } }; } @Override public String getHeader(String name) { return super.getHeader(name); } @Override public Enumeration<String> getHeaderNames() { return super.getHeaderNames(); } @Override public Enumeration<String> getHeaders(String name) { return super.getHeaders(name); } }
2、輔助類
HttpHelper
import java.io.BufferedReader; import java.io.IOException; import java.io.InputStream; import java.io.InputStreamReader; import java.nio.charset.Charset; import javax.servlet.ServletRequest; public class HttpHelper { /** * 獲取請求Body * * @param request * @return */ public static String getBodyString(ServletRequest request) { StringBuilder sb = new StringBuilder(); InputStream inputStream = null; BufferedReader reader = null; try { inputStream = request.getInputStream(); reader = new BufferedReader(new InputStreamReader(inputStream, Charset.forName("UTF-8"))); String line = ""; while ((line = reader.readLine()) != null) { sb.append(line); } } catch (IOException e) { e.printStackTrace(); } finally { if (inputStream != null) { try { inputStream.close(); } catch (IOException e) { e.printStackTrace(); } } if (reader != null) { try { reader.close(); } catch (IOException e) { e.printStackTrace(); } } } return sb.toString(); } }
3.自定義的filter
import java.io.IOException; import java.io.InputStream; import java.io.PrintWriter; import java.net.URL; import java.net.URLDecoder; import java.util.Map; 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 javax.servlet.http.HttpServletResponse; import javax.xml.crypto.URIDereferencer; import com.yt.util.HttpHelper; import com.yt.util.JsonHelper; public class VersionCheckFilter implements Filter { @Override public void destroy() { } @Override public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException { HttpServletRequest hreq = (HttpServletRequest) req; String uri = hreq.getRequestURI(); if(uri.contains("uploadImageServlet")){ //圖像上傳的請求，不做處理 chain.doFilter(req, res); }else{ String reqMethod = hreq.getMethod(); if("POST".equals(reqMethod)){ PrintWriter out = null; HttpServletResponse response = (HttpServletResponse) res; response.setCharacterEncoding("UTF-8"); response.setContentType("application/json; charset=utf-8"); /* String requestStr = this.inputStreamToString(hreq.getInputStream()); String[] arrs = requestStr.split("&"); for (String strs : arrs) { String[] strs2 = strs.split("="); for (int i = 0; i < strs2.length; i++) { if (strs2[0].equals("param")) { if (strs2[1] != null &&!strs2[1].equals("")) { System.out.println("test=" + strs2[1]); } } } }*/ ServletRequest requestWrapper = new BodyReaderHttpServletRequestWrapper(hreq); String body = HttpHelper.getBodyString(requestWrapper); //如果是POST請求則需要獲取 param 參數 String param = URLDecoder.decode(body,"utf-8"); //String param = hreq.getParameter("param"); //json串 轉換為Map if(param!=null&?m.contains("=")){ param = param.split("=")[1]; } Map paramMap = JsonHelper.getGson().fromJson(param, Map.class); Object obj_clientversion = paramMap.get("clientVersion"); String clientVersion = null; if(obj_clientversion != null){ clientVersion = obj_clientversion.toString(); System.out.println(clientVersion); /*try { out = response.getWriter(); Map remap = new HashMap<String, Object>(); remap.put("code", 9); remap.put("message", Constant.SYSTEM_ERR_DESC); out.append(JsonHelper.getGson().toJson(remap)); } catch (IOException e) { e.printStackTrace(); } finally { if (out != null) { out.close(); } }*/ chain.doFilter(requestWrapper, res); }else{ chain.doFilter(requestWrapper, res); } }else{ //get請求直接放行 chain.doFilter(req, res); } } } @Override public void init(FilterConfig arg0) throws ServletException { } /*public String inputStreamToString(InputStream in) throws IOException { StringBuffer out = new StringBuffer(); byte[] b = new byte[4096]; for (int n; (n = in.read(b)) != -1;) { out.append(new String(b, 0, n)); } return out.toString(); }*/ }
解決在Filter中讀取Request中的流後，後續controller或restful接口中無法獲取流的問題