// 源碼中適當(dāng)去除無關(guān)代碼
// 對于這類數(shù)據(jù)，SpringMVC 在 DispatchServlet 的 doDispatch() 方法中就會(huì)進(jìn)行處理。具體處理流程如下：
// org.springframework.web.servlet.DispatcherServlet.java
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
    HttpServletRequest processedRequest = request;
    HandlerExecutionChain mappedHandler = null;
    boolean multipartRequestParsed = false;
    WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
    processedRequest = checkMultipart(request);
    multipartRequestParsed = (processedRequest != request);
    // Determine handler for the current request.
    // other code...
}
// 1. 調(diào)用 checkMultipart(request)，當(dāng)前請求的數(shù)據(jù)類型是否為 multipart/form-data
protected HttpServletRequest checkMultipart(HttpServletRequest request) throws MultipartException {
    if (this.multipartResolver != null && this.multipartResolver.isMultipart(request)) {
		return this.multipartResolver.resolveMultipart(request);
    }
    return request;
}
//2. 如果是，調(diào)用 multipartResolver 的 resolveMultipart(request)，返回一個(gè) StandardMultipartHttpServletRequest 對象。
// org.springframework.web.multipart.support.StandardMultipartHttpServletRequest.java
public StandardMultipartHttpServletRequest(HttpServletRequest request) throws MultipartException {
    this(request, false);
}
public StandardMultipartHttpServletRequest(HttpServletRequest request, boolean lazyParsing) throws MultipartException {
    super(request);
    if (!lazyParsing) {
        parseRequest(request);
    }
}
// 3. 在構(gòu)造 StandardMultipartHttpServletRequest 對象時(shí)，會(huì)調(diào)用 parseRequest(request)，將 InputStream 中是數(shù)據(jù)流進(jìn)行進(jìn)一步的封裝。
// 不貼源碼了，主要是對 form-data 數(shù)據(jù)的封裝，包含字段和文件。

// 非 form-data 的數(shù)據(jù)，會(huì)存儲在 HttpServletRequest 的 InputStream 中。
// 在第一次調(diào)用 getParameterNames() 或 getParameter() 時(shí),
// 會(huì)調(diào)用 parseParameters() 方法對參數(shù)進(jìn)行封裝，從 InputStream 中讀取數(shù)據(jù)，并封裝到 Map 中。
//org.apache.catalina.connector.Request.java
public String getParameter(String name) {
    if (!this.parametersParsed) {
        this.parseParameters();
    }
    return this.coyoteRequest.getParameters().getParameter(name);
}

// 數(shù)據(jù)會(huì)直接會(huì)存儲在 HttpServletRequest 的 InputStream 中，通過 request.getInputStream() 或 getReader() 獲取。

// 上文講了在 doDispatch() 時(shí)就會(huì)進(jìn)行處理，因此這里會(huì)取不到值
log.info("input stream content: {}", new String(StreamUtils.copyToByteArray(request.getInputStream())));

// 第 1 次可以取到值
log.info("input stream content: {}", new String(StreamUtils.copyToByteArray(request.getInputStream())));
// 第一次執(zhí)行 getParameter() 會(huì)調(diào)用 parseParameters()，parseParameters 進(jìn)一步調(diào)用 getInputStream()
// 這里就取不到值了
log.info("form-data param: {}", request.getParameter("a"));
log.info("form-data param: {}", request.getParameter("b"));

// 第 1 次可以取到值
log.info("input stream content: {}", new String(StreamUtils.copyToByteArray(request.getInputStream())));
// 之后再任何地方再調(diào)用 getInputStream() 都取不到值，會(huì)拋出異常

/**
 * {@link javax.servlet.http.HttpServletRequest} wrapper that caches all content read from
 * the {@linkplain #getInputStream() input stream} and {@linkplain #getReader() reader},
 * and allows this content to be retrieved via a {@link #getContentAsByteArray() byte array}.
 * @see ContentCachingResponseWrapper
 */

@Slf4j
@WebFilter(urlPatterns = "/*")
public class CachingContentFilter implements Filter {
    private static final String FORM_CONTENT_TYPE = "multipart/form-data";
    @Override
    public void init(FilterConfig filterConfig) {
    }
    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
                         FilterChain chain) throws IOException, ServletException {
        String contentType = request.getContentType();
        if (request instanceof HttpServletRequest) {
            HttpServletRequest requestWrapper = new ContentCachingRequestWrapper((HttpServletRequest) request);
            // #1
            if (contentType != null && contentType.contains(FORM_CONTENT_TYPE)) {
                chain.doFilter(request, response);
            } else {
                chain.doFilter(requestWrapper, response);
            }
            return;
        }
        chain.doFilter(request, response);
    }
    @Override
    public void destroy() {
    }
}
// 添加掃描 filter 注解
@ServletComponentScan
@SpringBootApplication
public class SeedApplication {
    public static void main(String[] args) {
        SpringApplication.run(SeedApplication.class, args);
    }
}

// 流數(shù)據(jù)獲取，比如 json
// #2
String jsonBody = IOUtils.toString(wrapper.getContentAsByteArray(), "utf-8");
// form-data 和 urlencoded 數(shù)據(jù)
String paramA = request.getParameter("paramA");
Map<String,String[]> params = request.getParameterMap();

package com.example.seed.common.config;
import lombok.extern.slf4j.Slf4j;
import org.springframework.web.util.ContentCachingRequestWrapper;
import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import java.io.IOException;
/**
 * @author Fururur
 * @date 2020/5/6-14:26
 */
@Slf4j
@WebFilter(urlPatterns = "/*")
public class CachingContentFilter implements Filter {
    private static final String FORM_CONTENT_TYPE = "multipart/form-data";
    @Override
    public void init(FilterConfig filterConfig) {
    }
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        String contentType = request.getContentType();
        if (request instanceof HttpServletRequest) {
            HttpServletRequest requestWrapper = new ContentCachingRequestWrapper((HttpServletRequest) request);
            if (contentType != null && contentType.contains(FORM_CONTENT_TYPE)) {
                chain.doFilter(request, response);
            } else {
                chain.doFilter(requestWrapper, response);
            }
            return;
        }
        chain.doFilter(request, response);
    }
    @Override
    public void destroy() {
    }
}
package com.example.seed;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.servlet.ServletComponentScan;
@ServletComponentScan
@SpringBootApplication
public class SeedApplication {
    public static void main(String[] args) {
        SpringApplication.run(SeedApplication.class, args);
    }
}
@RequestMapping("/query")
public void query(HttpServletRequest request) {
    ContentCachingRequestWrapper wrapper = new ContentCachingRequestWrapper(request);
    log.info("{}", new String(wrapper.getContentAsByteArray()));
}