RequestBody只能讀取一次的問題

一、為什么只能讀一次

原因很簡單：因為是流。想想看，java中的流也是只能讀一次，因為讀完之后，position就到末尾了。

二、解決辦法

思路：第一次讀的時候，把流數據暫存起來。后面需要的時候，直接把暫存的數據返回出去。

實現邏輯：

1. 自定義一個HttpServletRequestWrapper，覆寫getInputStream()和getReader()方法。
2. 增加一個Filter，在doFilter()中啟用自定義的Wrapper

三、代碼

1、自定義的Wrapper

import javax.servlet.ReadListener;
import javax.servlet.ServletInputStream;
import javax.servlet.ServletRequest;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.nio.charset.Charset;

public class BodyReaderHttpServletRequestWrapper extends HttpServletRequestWrapper {
    private final byte[] body;

    public BodyReaderHttpServletRequestWrapper(HttpServletRequest request) throws IOException {
        super(request);
        String sessionStream = getBodyString(request);
        body = sessionStream.getBytes(Charset.forName("UTF-8"));
    }

    private String getBodyString(ServletRequest request) throws IOException {
        StringBuilder sb = new StringBuilder();
        InputStream ins = request.getInputStream();

        try (BufferedReader isr = new BufferedReader(new InputStreamReader(ins, Charset.forName("UTF-8")));) {
            String line = "";
            while ((line = isr.readLine()) != null) {
                sb.append(line);
            }
        } catch (IOException e) {
            throw e;
        }
        return sb.toString();
    }

    @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 boolean isFinished() {
                return bais.available() == 0;
            }

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

            @Override
            public void setReadListener(ReadListener readListener) {
            }
        };
    }
}

2、加個Filter來啟用wrapper

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.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import java.io.IOException;

// 啟用Filter需要在Springboot的啟動類加@ServletComponentScan
@WebFilter(filterName = "bodyReaderFilter", urlPatterns = "/*")
public class BodyReaderFilter implements Filter {

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

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest httpServletRequest = (HttpServletRequest) servletRequest;
        ServletRequest requestWrapper = new BodyReaderHttpServletRequestWrapper(httpServletRequest);
        filterChain.doFilter(requestWrapper, servletResponse);
    }

    @Override
    public void destroy() {
    }

}