HttpServletRequest读取body只可读取一次的解决方案

HttpServletRequest读取body只可读取一次的解决方案

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什么时候需要读取多次body：

当过滤器、拦截器、控制器需要使用请求的body两次以上；前两者执行的操作一般为对数据的验证与提前处理，而控制器执行的操作为对业务的处理。

为什么HttpServletRequest对象的请求体body只读取一次：

HttpServletRequest使用getInputStream()与getReader()获取输入流因为读取时数据流指针的单向移动导致请求的body内容只可读取一次。

怎么解决HttpServletRequest对象的请求体body只读取一次：

使用包装类以继承方式包装HttpServletRequest类，将请求body的内容提前读取到包装类新属性body，并重写getInputStream()与getReader()的方法将对请求数据流的使用转为对body的使用。

包装类代码：

package com.common.filters;

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

//包装类，HttpServletRequestWrapper实现HttpServletRequest
public class RequestWrapper extends HttpServletRequestWrapper {

    private final String body;

    public RequestWrapper(HttpServletRequest request) throws IOException {
        super(request);
        StringBuilder stringBuilder = new StringBuilder();
        BufferedReader bufferedReader = null;
        try {
            InputStream inputStream = request.getInputStream();
            if (inputStream != null) {
                bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
                char[] charBuffer = new char[128];
                int bytesRead = -1;
                while ((bytesRead = bufferedReader.read(charBuffer)) > 0) {
                    stringBuilder.append(charBuffer, 0, bytesRead);
                }
            } else {
                stringBuilder.append("");
            }
        } catch (IOException ex) {
            throw ex;
        } finally {
            if (bufferedReader != null) {
                try {
                    bufferedReader.close();
                } catch (IOException ex) {
                    throw ex;
                }
            }
        }
        body = stringBuilder.toString();
    }
    
//每个getInputStream的方法都是根据body字符串创建新输入流
    @Override
    public ServletInputStream getInputStream() throws IOException {
        final ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(body.getBytes());
        ServletInputStream servletInputStream = new ServletInputStream() {
            public int read() throws IOException {
                return byteArrayInputStream.read();
            }
        };
        return servletInputStream;
    }

//每个getBufferReader的方法都是根据body字符串创建新Reader读取流
    @Override
    public BufferedReader getReader() throws IOException {
        return new BufferedReader(new InputStreamReader(this.getInputStream()));
    }

//获取body字符串，单例
    public String getBody() {
        return this.body;
    }
}

怎么将包装类对象替换原HttpServletRequest对象：

包装类对象替换原HttpServletRequest对象，根据SpringMVC的执行顺序与参数传递，在过滤器Filter的chain.doFilter()中完成替换。注意，不可在拦截器中，因为拦截器无法以代码方式进行HttpServletRequest对象替换。

过滤器代码如下：

package com.common.filters;

import javax.servlet.*;
import org.springframework.stereotype.Component;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import java.io.IOException;


@Component
@WebFilter(filterName = "RequestWrapperFilter", urlPatterns = "/*")
public class RequestWrapperFilter implements Filter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {

        ServletRequest requestWrapper = null;
        if (request instanceof HttpServletRequest) {
            requestWrapper = new RequestWrapper((HttpServletRequest) request);
        }
        if (null == requestWrapper) {
            chain.doFilter(request, response);
        } else {
            chain.doFilter(requestWrapper, response);
        }

    }

    @Override
    public void destroy() {

    }
}