ContentCachingRequestWrapper个人理解

ContentCachingRequestWrapper个人理解，如有理解错误的地方，欢迎指正

参考这篇博客

https://blog.youkuaiyun.com/f641385712/article/details/87814153

背景：request.getInputStream()获取请求body里面的内容只能被获取一次，ContentCachingRequestWrapper通过这个类能够解决解决HttpServletRequest inputStream只能读取一次的问题，但是这个类有缺陷（前提必须是doFilter之前不能使用request.getInputStream()方法）

分析：

cachedContent来缓存body体里面的内容。但最重要的是，什么时候才会向cachedCotent里面写内容呢？

1.程序在运行过程中会调用ContentCachingRequestWrapper的getInputStream()方法

    public ServletInputStream getInputStream() throws IOException {
        if (this.inputStream == null) {
            this.inputStream = new ContentCachingRequestWrapper.ContentCachingInputStream(this.getRequest().getInputStream());
        }

        return this.inputStream;
    }

注意，这里使用了一次getInputStream()方法

2.随后调用请求流的read()方法，把内容缓存起来（@RequestBody注解的参数解析器(RequestResponseBodyMethodProcessor)就是调用了read()方法去获取到内容的）

private class ContentCachingInputStream extends ServletInputStream {
        private final ServletInputStream is;

        public ContentCachingInputStream(ServletInputStream is) {
            this.is = is;
        }

        public int read() throws IOException {
            int ch = this.is.read();
            if (ch != -1) {
                ContentCachingRequestWrapper.this.cachedContent.write(ch);
            }

            return ch;
        }
    }

改善这种缺陷的方案：第一次读取了inputStream之后，缓存起来，然后再通过重写getInputStream()方法再将数据写回去

下面这个代码是参考上面那个链接的

public class ContentCachingRequestWrapper extends HttpServletRequestWrapper{
    
    private byte[] body;
    
    private BufferedReader reader;

    private ServletInputStream inputStream;

    public ContentCachingRequestWrapper(HttpServletRequest request) throws IOException{
        super(request);
        //读一次 然后缓存起来
        body = IOUtils.toByteArray(request.getInputStream());
        inputStream = new RequestCachingInputStream(body);
    }
    
    public byte[] getBody() {
        return body;
    }
    
    @Override
    public ServletInputStream getInputStream() throws IOException {
        if (inputStream != null) {          
            return inputStream;
        }
        return super.getInputStream();
    }

    @Override
    public BufferedReader getReader() throws IOException {
        if (reader == null) {
            reader = new BufferedReader(new InputStreamReader(inputStream, getCharacterEncoding()));
        }
        return reader;
    }
    
    //代理一下ServletInputStream 里面真是内容为当前缓存的bytes
    private static class RequestCachingInputStream extends ServletInputStream {
        
        private final ByteArrayInputStream inputStream;

        public RequestCachingInputStream(byte[] bytes) {
            inputStream = new ByteArrayInputStream(bytes);
        }
        @Override
        public int read() throws IOException {
            return inputStream.read();
        }

        @Override
        public boolean isFinished() {
            return inputStream.available() == 0;
        }

        @Override
        public boolean isReady() {
            return true;
        }

        @Override
        public void setReadListener(ReadListener readlistener) {
        }

    }
    
}

或者我这种写法

import org.springframework.util.StringUtils;

import javax.servlet.ReadListener;
import javax.servlet.ServletInputStream;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import java.io.*;


public class RequestWrapper extends HttpServletRequestWrapper {

    private String requestBody = null;
    HttpServletRequest req = null;
    private Cookie[] cookies;

    public RequestWrapper(HttpServletRequest request, String requestBody) throws IOException {
        super(request);
        this.requestBody = requestBody;
        this.req = request;
    }
    @Override
    public BufferedReader getReader() throws IOException {
        return new BufferedReader(new StringReader(requestBody));
    }

    @Override
    public ServletInputStream getInputStream() throws IOException {
        return new ServletInputStream() {
            @Override
            public boolean isFinished() {
                return false;
            }

            @Override
            public boolean isReady() {
                return false;
            }

            @Override
            public void setReadListener(ReadListener readListener) {

            }

            private InputStream in = new ByteArrayInputStream(
                    requestBody.getBytes(StringUtils.isEmpty(req.getCharacterEncoding())?"UTF-8":req.getCharacterEncoding()));

            @Override
            public int read() throws IOException {
                return in.read();
            }
        };
    }

    @Override
    public Cookie[] getCookies() {
        return cookies;
    }

    public void setCookies(Cookie[] cookies) {
        this.cookies = cookies;
    }
}