首先我们来描述一下在开发中遇到的问题，场景如下：
比如我们要拦截所有请求，获取请求中的某个参数，进行相应的逻辑处理：比如我要获取所有请求中的公共参数 token,clientVersion等等；这个时候我们通常有两种做法
前提条件是我们实现Filter类，重写doFilter方法
1、通过getParameter方法获得
HttpServletRequest hreq = (HttpServletRequest) req;
String param = hreq.getParameter("param");
这种方法有缺陷：它只能获取 POST 提交方式中的
Content-Type: application/x-www-form-urlencoded;
这种提交方式中，key为param ,若提交类型不是这种方式就获取不到param的值
2、获取请求对象中的数据流，通过解析流信息来获取提交的内容；代码示例如下：
[java] view plain copy
/**
* 获取请求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();
}
通过这种简单的解析方式，将http请求中的body解析成 字符串的形式；然后再对字符串的格式进行业务解析；
这种处理方式的优点是：能解析 出content-Type 为 application/x-www-form-urlencoded ，application/json , text/xml 这三种提交方式的 数据 （至于另外一种带文件的请求：multipart/form-data ，本人没有亲自测试过，等后期遇到此类为题再来解决）。 上述方法返回的可能是key,value(对应第一种content-type),可能是json字符串（对应第二种），可能是xml的字符串（对应第三种）
但是这种方式有一个很大的缺点：那就是当从请求中获取流以后，流被filter中的这个 inputStreamToString(InputStream in) 这个方法处理后就被“消耗”了，这会导致，chain.doFilter(request, res)这个链在传递 request对象的时候，里面的请求流为空，导致责任链模式下，其他下游的链无法获取请求的body,从而导致程序无法正常运行，这也使得我们的这个filter虽然可以获取请求信息，但是它会导致整个应用程序不可用，那么它也就失去了意义；
针对第二种方式的缺陷：流一旦被读取，就无法向下传递整个问题，有如下解决方案；
解决思路如下：将取出来的字符串，再次转换成流，然后把它放入到新request 对象中，在chain.doFiler方法中 传递新的request对象；要实现这种思路，需要自定义一个类
继承HttpServletRequestWrapper，然后重写public BufferedReader getReader()方法，public ServletInputStream getInputStream()方法；（这两个方法的重写实现逻辑如下：getInputStream（）方法中将body体中的字符串转换为字节流（它实质上返回的是一个ServletInputStream 对象）；然后通过getReader()调用---->getInputStream（）方法；），继承实现重写逻辑以后，在自定义分filter（VersionCheckFilter）中，使用自定义的HttpServletRequestWrapper（BodyReaderHttpServletRequestWrapper）将原始的HttpServletRequest对象进行再次封装；再通过BodyReaderHttpServletRequestWrapper对象去做dofilter(req,res)的req对象；
涉及的三个类的代码如下：
自定义的HttpServletRequestWrapper
[java] view plain copy
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、辅助类
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 {
/**
* 获取请求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.自定义的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")){
//图像上传的请求，不做处理
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请求则需要获取 param 参数
String param = URLDecoder.decode(body,"utf-8");
//String param = hreq.getParameter("param");
//json串 转换为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请求直接放行
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();
}*/
}