解決在Filter中讀取Request中的流後，後續controller或restful介面中無法獲取流的問題
阿新 • • 發佈：2019-01-02
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，獲取請求中的某個引數，進行相應的邏輯處理：比如我要獲取所有請求中的公共引數 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 ,若提交型別不是這種方式就獲取不到param的值
2、獲取請求物件中的資料流，通過解析流資訊來獲取提交的內容；程式碼示例如下：
/** * 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 字串的形式；然後再對字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 資料 （至於另外一種帶檔案的請求：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字串（對應第二種），可能是xml的字串（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物件的時候，裡面的請求流為空，導致責任鏈模式下，其他下游的鏈無法獲取請求的body,從而導致程式無法正常執行，這也使得我們的這個filter雖然可以獲取請求資訊，但是它會導致整個應用程式不可用，那麼它也就失去了意義；
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：將取出來的字串，再次轉換成流，然後把它放入到新request 物件中，在chain.doFiler方法中 傳遞新的request物件；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體中的字串轉換為位元組流（它實質上返回的是一個ServletInputStream
物件）；然後通過getReader()呼叫---->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物件進行再次封裝；再通過BodyReaderHttpServletRequestWrapper物件去做dofilter(req,res)的req物件；
涉及的三個類的程式碼如下：
自定義的HttpServletRequestWrapper
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.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")){
//影象上傳的請求，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 引數
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();
}*/
}