使用AOP在切面逻辑中无法获取到requesetBody

使用场景：在接口处理之前，我们需要拿到请求参数，对参数进行校验。注意，这里需要拿到的是原始的请求信息！

一般的获取方式

ServletInputStream inputStream = request.getInputStream();
StringBuilder stringBuilder = new StringBuilder();
try (BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream, request.getCharacterEncoding()))) {
    String line;
    while ((line = reader.readLine()) != null) {
        stringBuilder.append(line);
    }
} catch (IOException e) {
    e.printStackTrace();
}
String requestBody = stringBuilder.toString();

获取requestBody的代码大同小异，可自行搜索。代码没有问题，但是无法获取到requestBody，就要考虑接口方法是否使用了@RequestBody。

在Spring MVC框架中，当你使用@RequestBody注解时，Spring会在将请求转发到控制器方法之前，从HTTP请求体中读取数据并将其反序列化为Java对象。这一处理过程是由HttpMessageConverter完成的，它负责将请求体中的JSON、XML或其他格式的数据转换为Java对象。

请求体只能被读取一次：HTTP请求体是一个输入流，它只能被读取一次。一旦HttpMessageConverter读取了请求体，输入流就被“消耗”掉了，无法再次被读取。因此，当切面尝试访问请求体时，它发现输入流已经为空或不可用。

解决方法：

import javax.servlet.ReadListener;
import javax.servlet.ServletInputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.nio.charset.StandardCharsets;

public class CachedBodyHttpServletRequestWrapper extends HttpServletRequestWrapper {

    private final byte[] cachedBody;

    public CachedBodyHttpServletRequestWrapper(HttpServletRequest request) throws IOException {
        super(request);
        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
        InputStream inputStream = request.getInputStream();
        byte[] buffer = new byte[1024];
        int bytesRead;
        while ((bytesRead = inputStream.read(buffer)) != -1) {
            outputStream.write(buffer, 0, bytesRead);
        }
        cachedBody = outputStream.toByteArray();
    }

    @Override
    public ServletInputStream getInputStream() throws IOException {
        final ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(cachedBody);
        return new ServletInputStream() {
            @Override
            public boolean isFinished() {
                return byteArrayInputStream.available() == 0;
            }

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

            @Override
            public void setReadListener(ReadListener readListener) {
            }

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

    public String getCachedBody() {
        return new String(cachedBody, StandardCharsets.UTF_8);
    }
}

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 java.io.IOException;

public class CachedBodyFilter implements Filter {

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

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        if (request instanceof HttpServletRequest) {
            HttpServletRequest httpRequest = (HttpServletRequest) request;
            CachedBodyHttpServletRequestWrapper cachedBodyRequestWrapper = new CachedBodyHttpServletRequestWrapper(httpRequest);
            chain.doFilter(cachedBodyRequestWrapper, response);
        } else {
            chain.doFilter(request, response);
        }
    }

    @Override
    public void destroy() {
    }
}

import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class FilterConfig {

    @Bean
    public FilterRegistrationBean<CachedBodyFilter> loggingFilter(){
        FilterRegistrationBean<CachedBodyFilter> registrationBean 
          = new FilterRegistrationBean<>();

        registrationBean.setFilter(new CachedBodyFilter());
        registrationBean.addUrlPatterns("/*");

        return registrationBean;    
    }
}

然后在切面里利用CachedBodyHttpServletRequestWrapper 去获取requestBody就可以了。