Request的包装类HttpServletRequestWrapper的使用

忘是亡心i 2022-05-27 13:52 221阅读 0赞

在使用zuul进行鉴权的时候，我们希望从请求Request中获取输入流，解析里面的内容，奈何InputStream只能被读取一次。为啥呢？源码里是这样说的：

> public int read(byte\[\] b,int off, int len)  
> 　　　Reads up to len bytes of data into an array of bytes from this input stream. Ifpos equals count, then -1 is returned to indicate end of file. Otherwise, the number k of bytes read is equal to the smaller of len and count-pos.If k is positive, then bytes buf\[pos\] through buf\[pos+k-1\] are copied into b\[off\] through b\[off+k-1\] in the manner performed by System.arraycopy. The value k is added into pos and k is returned.  
> 　　　  
> 大致的意思是：在InputStream读取的时候，会有一个pos指针，它指示每次读取之后下一次要读取的起始位置。在每次读取后会更新pos的值，当你下次再来读取的时候是从pos的位置开始的，而不是从头开始，所以第二次获取String中的值的时候是不全的，API中提供了一个解决办法：reset()。但我发现在inputStream和servlet中根本不起作用。提示 mark/reset not supported 。意思是只有重写过markSupported()方法的IO流才可以用。所以一般我们使用inputStream，最好在一次内处理完所有逻辑。

那么就没法在中途获取请求流中的数据么？当然有办法了，我可是PPZ，只需要重写Request缓存一下流中的数据就好了，实现代码如下：

BodyReaderHttpServletRequestWrapper.java
    
    package com.neo.authUtils;
    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 java.util.NoSuchElementException;
    
    import javax.servlet.ReadListener;
    import javax.servlet.ServletInputStream;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletRequestWrapper;  
    
    public class BodyReaderHttpServletRequestWrapper extends HttpServletRequestWrapper {   
    
       // private final byte[] body; 
         -----》private byte[] body;《------- 
    
        public BodyReaderHttpServletRequestWrapper(HttpServletRequest request) throws IOException {  
            super(request);  
            System.out.println("-------------------打印请求的头信息------------------------------");    
            Enumeration<?> e = request.getHeaderNames()   ;    
             while(e.hasMoreElements()){    
                 String name = (String) e.nextElement();    
                 String value = request.getHeader(name);    
                // System.out.println(name+" = "+value); 
    
             }
             -----》获取流中的数据缓存到字节数组中，以后要读数据就用这里的《------
            body = HttpHelper.getBodyString(request).getBytes(Charset.forName("UTF-8"));  
        }
    
        /** * 从请求的头部获取用户的身份识别id; * @param request * @return */
        public String getJsessionidFromHeader(HttpServletRequest request) {
            String jsessionid = null;//识别用户身份的id;
            Enumeration<?> e = request.getHeaderNames()   ;    
            while(e.hasMoreElements()){    
                String name = (String) e.nextElement();    
                String value = request.getHeader(name);
                //cookie = JSESSIONID=B926F6024438D4C693A5E5881595160C; SESSION=458e80dc-e354-4af3-a501-74504a873e70
                if("cookie".equals(name)) {
                    jsessionid = value.split(";")[0].split("=")[1];
                }
                System.out.println(name+"="+value);
            }
           // System.out.println("======jsessionid========>"+jsessionid);
            return jsessionid;
        }
    
        @Override  
        public BufferedReader getReader() throws IOException {  
            return new BufferedReader(new InputStreamReader(getInputStream()));  
        }  
    
        @Override  
        public ServletInputStream getInputStream() throws IOException {  
             ------》从缓存的数据中读取数据《------
            final ByteArrayInputStream bais = new ByteArrayInputStream(body);  
    
            return new ServletInputStream() {  
                public int read() throws IOException {  
                    return bais.read();  
                }
    
                @Override
                public boolean isFinished() {
                    // TODO Auto-generated method stub
                    return false;
                }
    
                @Override
                public boolean isReady() {
                    // TODO Auto-generated method stub
                    return false;
                }
    
                @Override
                public void setReadListener(ReadListener listener) {
                    // TODO Auto-generated method stub
    
                }  
            };  
        }  
    
        @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); } */
    
        /** * content-type=text/plain;charset=UTF-8 * 重写getHeaders方法，实现自定义Content-Type; */
        @Override  
        public Enumeration<String> getHeaders(String name) {  
            if ((null != name && name.equals("Content-Type"))||(null != name && name.equals("content-type"))) {  
                return new Enumeration<String>() {  
                    private boolean hasGetted = false;  
    
                    @Override  
                    public String nextElement() {  
                        if (hasGetted) {  
                            throw new NoSuchElementException();  
                        } else {  
                            hasGetted = true;
                            return "application/json;charset=utf-8";  
                        }  
                    }  
    
                    @Override  
                    public boolean hasMoreElements() {  
                        return !hasGetted;  
                    }  
                };  
            }  
            return super.getHeaders(name);  
        }  
    
        /** * 添加自定义信息到请求体; * @param customMsg：自定义的添加到请求体中的信息; */
        public void appendCustomMsgToReqBody(String customMsg) {
            String oldBodyString = HttpHelper.getBodyString(this);//oldBodyString一定是通过当前对象的输入流解析得来的，否则接收时会报EOFException；
            String appendMsg = HttpHelper.appendCustomMsgToReqBody(customMsg);
            String requestBodyAfterAppend = appendMsg + "," +oldBodyString;
            //this.body = HttpHelper.appendCustomMsgToReqBody(HttpHelper.appendCustomMsgToReqBody(customMsg)+(HttpHelper.getBodyString(this))).getBytes(Charset.forName("UTF-8"));
            //this.body = HttpHelper.appendCustomMsgToReqBody((HttpHelper.getBodyString(this))).getBytes(Charset.forName("UTF-8"));
            this.body = HttpHelper.appendCustomMsgToReqBody(requestBodyAfterAppend).getBytes(Charset.forName("UTF-8"));
        } 
    }  
    
    
    HttpHelper.java
    
    package com.neo.authUtils;
    
    import java.io.BufferedReader;
    import java.io.ByteArrayInputStream;
    import java.io.IOException;
    import java.io.InputStream;
    import java.io.InputStreamReader;
    import java.io.UnsupportedEncodingException;
    import java.nio.charset.Charset;
    
    import javax.servlet.ServletRequest;
    
    public class HttpHelper { 
        /** * 获取post请求中的Body * * @param request * @return */
        public static String getBodyString(ServletRequest request) {
            StringBuilder sb = new StringBuilder();
            InputStream inputStream = null;
            BufferedReader reader = null;
            try {
                inputStream = request.getInputStream();
                //读取流并将流写出去,避免数据流中断;
                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();
        }
    
        //添加自定义的信息到请求体中;
        public static String appendCustomMsgToReqBody(String newReqBodyStr) {
            StringBuilder sb = new StringBuilder();
            InputStream inputStream = null;
            BufferedReader reader = null;
            String newReqBody = null;
            try {
                //通过字符串构造输入流;
                inputStream = String2InputStream(newReqBodyStr);
                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();
                    }
                }
            }
            //返回字符串;
            newReqBody = sb.toString();
            return newReqBody;
    
        }
    
        //将字符串转化为输入流;
        public static InputStream String2InputStream(String str) {
            ByteArrayInputStream stream = null;
            try {
                stream = new ByteArrayInputStream(str.getBytes("UTF-8"));
            } catch (UnsupportedEncodingException e) {
                e.printStackTrace();
            }
            return stream;
        }
    }

上述方案解决了使用request.getInpuStream()方法读取流中的数据只能读取一次的问题，其实当我们在使用第三方接口时，如果请求头信息和我们的服务所需不一致，例如第三方接口中头部信息为：content-type=text/plain;charset=UTF-8  
而我们需要的是：”application/json;charset=utf-8”时，我们也是可以通过重写对应的方法对请求的头部信息进行修改的，代码如下：

/** * content-type=text/plain;charset=UTF-8 * 重写getHeaders方法，实现自定义Content-Type; */
        @Override  
        public Enumeration<String> getHeaders(String name) {  
            if ((null != name && name.equals("Content-Type"))||(null != name && name.equals("content-type"))) {  
                return new Enumeration<String>() {  
                    private boolean hasGetted = false;  
    
                    @Override  
                    public String nextElement() {  
                        if (hasGetted) {  
                            throw new NoSuchElementException();  
                        } else {  
                            hasGetted = true;
                            return "application/json;charset=utf-8";  
                        }  
                    }  
    
                    @Override  
                    public boolean hasMoreElements() {  
                        return !hasGetted;  
                    }  
                };  
            }  
            return super.getHeaders(name);  
        }

当我们在后端设置了头部信息后，如果不出意外，前端发送的请求将变为简单请求，这样，服务器的处理机制将简单很多。