springboot使用undertow作为web容器而引发的中文乱码问题

 先说一下出现这种情况的场景。该场景在使用jetty,tomcat作为容器时是可以正常运行的。首先是表单提交。

 springmvc控制器代码如下:

@RequestMapping("test")
@Controller
public class TestController {

    @RequestMapping("aa.html")
    public String aa(Model model, RedirectAttributes redirectAttributes) {
        redirectAttributes.addAttribute("a","李四");
        return  "redirect:bb.html";
    }

    @RequestMapping("bb.html")
    public String bb(Model model, HttpServletRequest request) {
        String a=request.getParameter("a");
        return "login";
    }
}

 aa方法做了一次重定向，重定向时传参是中文，到进入bb方法时，获取到的string a则为乱码。

查看项目已使用了spring提供的字符集设置过滤器CharacterEncodingFilter。强制设置字符集为utf-8。却依然出现乱码问题。

     没办法，只能查看springmvc的源码。跟踪源码后发现，在RedirectView类的createTargetUrl方法里，会去为重定向拼装url字符串：

protected final String createTargetUrl(Map model, HttpServletRequest request)
			throws UnsupportedEncodingException {

		// Prepare target URL.
		StringBuilder targetUrl = new StringBuilder();
		if (this.contextRelative && getUrl().startsWith("/")) {
			// Do not apply context path to relative URLs.
			targetUrl.append(request.getContextPath());
		}
		targetUrl.append(getUrl());

		String enc = this.encodingScheme;
		if (enc == null) {
			enc = request.getCharacterEncoding();
		}
		if (enc == null) {
			enc = WebUtils.DEFAULT_CHARACTER_ENCODING;
		}

		if (this.expandUriTemplateVariables && StringUtils.hasText(targetUrl)) {
			Map variables = getCurrentRequestUriVariables(request);
			targetUrl = replaceUriTemplateVariables(targetUrl.toString(), model, variables, enc);
		}
		if (isPropagateQueryProperties()) {
		 	appendCurrentQueryParams(targetUrl, request);
		}
		if (this.exposeModelAttributes) {
			appendQueryProperties(targetUrl, model, enc);
		}

		return targetUrl.toString();
	}

 debug发现，在使用post做form表单提交时，request.getCharacterEncoding()获得的是null，故导致执行到了enc = WebUtils.DEFAULT_CHARACTER_ENCODING这行代码

public static final String DEFAULT_CHARACTER_ENCODING = "ISO-8859-1";

 使用了ISO-8859-1，故导致重定向的url字符串里没有使用utf-8字符集，导致了乱码。

      那为什么request.getCharacterEncoding()获得的是null呢。在CharacterEncodingFilter过滤器里，

@Override
	protected void doFilterInternal(
			HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
			throws ServletException, IOException {

		String encoding = getEncoding();
		if (encoding != null) {
			if (isForceRequestEncoding() || request.getCharacterEncoding() == null) {
				request.setCharacterEncoding(encoding);
			}
			if (isForceResponseEncoding()) {
				response.setCharacterEncoding(encoding);
			}
		}
		filterChain.doFilter(request, response);
	}

 该过滤器会强制使用utf-8。在debug之后，发现request.setCharacterEncoding(encoding)这行代码确实有执行到。再看request.setCharacterEncoding方法里的实现，io.undertow.servlet.spec.HttpServletRequestImpl:

@Override
    public void setCharacterEncoding(final String env) throws UnsupportedEncodingException {
        if (readStarted) {
            return;
        }
        try {
            characterEncoding = Charset.forName(env);

            final ManagedServlet originalServlet = exchange.getAttachment(ServletRequestContext.ATTACHMENT_KEY).getOriginalServletPathMatch().getServletChain().getManagedServlet();
            final FormDataParser parser = originalServlet.getFormParserFactory().createParser(exchange);
            if (parser != null) {
                parser.setCharacterEncoding(env);
            }
        } catch (UnsupportedCharsetException e) {
            throw new UnsupportedEncodingException();
        }
    }

 debug发现，readStarted为true。故CharacterEncodingFilter过滤器设置request.setCharacterEncoding无效。

注意，HttpServletRequestImpl是undertow容器的实现，springboot集成了undertow作为web服务器。

     在HttpServletRequestImpl的private FormData parseFormData()方法上设置断点，发现在进入CharacterEncodingFilter过滤器前，undertow容器会先进入parseFormData方法，调用堆栈如下：

at io.undertow.servlet.spec.HttpServletRequestImpl.parseFormData(HttpServletRequestImpl.java:750)
	  at io.undertow.servlet.spec.HttpServletRequestImpl.getParameter(HttpServletRequestImpl.java:636)
	  at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:70)
	  at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
	  at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61)
	  at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131)
	  at io.undertow.servlet.handlers.FilterHandler.handleRequest(FilterHandler.java:84)
	  at io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:62)
	  at io.undertow.servlet.handlers.ServletDispatchingHandler.handleRequest(ServletDispatchingHandler.java:36)
	  at io.undertow.servlet.handlers.security.SSLInformationAssociationHandler.handleRequest(SSLInformationAssociationHandler.java:131)
	  at io.undertow.servlet.handlers.security.ServletAuthenticationCallHandler.handleRequest(ServletAuthenticationCallHandler.java:57)
	  at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
	  at io.undertow.security.handlers.AbstractConfidentialityHandler.handleRequest(AbstractConfidentialityHandler.java:46)
	  at io.undertow.servlet.handlers.security.ServletConfidentialityConstraintHandler.handleRequest(ServletConfidentialityConstraintHandler.java:64)
	  at io.undertow.security.handlers.AuthenticationMechanismsHandler.handleRequest(AuthenticationMechanismsHandler.java:60)
	  at io.undertow.servlet.handlers.security.CachedAuthenticatedSessionHandler.handleRequest(CachedAuthenticatedSessionHandler.java:77)
	  at io.undertow.security.handlers.AbstractSecurityContextAssociationHandler.handleRequest(AbstractSecurityContextAssociationHandler.java:43)
	  at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
	  at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
	  at io.undertow.servlet.handlers.ServletInitialHandler.handleFirstRequest(ServletInitialHandler.java:285)
	  at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:264)
	  at io.undertow.servlet.handlers.ServletInitialHandler.access$000(ServletInitialHandler.java:81)
	  at io.undertow.servlet.handlers.ServletInitialHandler$1.handleRequest(ServletInitialHandler.java:175)
	  at io.undertow.server.Connectors.executeRootHandler(Connectors.java:207)
	  at io.undertow.server.HttpServerExchange$1.run(HttpServerExchange.java:802)
	  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
	  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	  at java.lang.Thread.run(Thread.java:744)

 parseFormData()如下：

private FormData parseFormData() {
        if (parsedFormData == null) {
            if (readStarted) {
                return null;
            }
            final ManagedServlet originalServlet = exchange.getAttachment(ServletRequestContext.ATTACHMENT_KEY).getCurrentServlet().getManagedServlet();
            final FormDataParser parser = originalServlet.getFormParserFactory().createParser(exchange);
            if (parser == null) {
                return null;
            }
            readStarted = true;
            try {
                return parsedFormData = parser.parseBlocking();
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
        return parsedFormData;
    }

 注意，该方法把readStarted设置为true，所以在进入CharacterEncodingFilter过滤器后，调用request.setCharacterEncoding时，其实什么都没有处理，则导致springmvc在拼装重定向url字符串时，没有使用utf-8字符集，导致出现了乱码。至此出现乱码的原因分析完毕。至于为什么容器会去调用 parseFormData()，大家可以查看调用堆栈里每一步的实现，看看是怎么一步步调用到parseFormData()，我觉得这是undertow容器的一个bug。

        分析完原因，给出解决方案，这样才完整。我这里的解决方案是添加一个web过滤器，利用装饰器模式，改写request.getCharacterEncoding()方法，当该方法获得为空时，默认返回utf-8。

Utf8EncodingFilter：

package com.onlyou.superp2b;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.web.filter.GenericFilterBean;

import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import java.io.IOException;

/**
 * 默认使用utf-8字符集
 * Created by cd_huang on 2017/7/25.
 */
public class Utf8EncodingFilter extends GenericFilterBean {
	private static Logger logger = LoggerFactory.getLogger(Utf8EncodingFilter.class);
	@Override
	public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
		Utf8EncodingRequest request =new Utf8EncodingRequest((HttpServletRequest)servletRequest);
		filterChain.doFilter(request,servletResponse);
	}

	protected void initFilterBean() throws ServletException {
		logger.info("---加载Utf8EncodingFilter！---");
	}
}

 Utf8EncodingRequest：

package com.onlyou.superp2b;

import org.apache.commons.lang3.StringUtils;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;

/**
 * 默认使用utf-8字符集
 * Created by cd_huang on 2017/7/25.
 */
public class Utf8EncodingRequest extends HttpServletRequestWrapper {

	public Utf8EncodingRequest(HttpServletRequest request) {
		super(request);
	}
	@Override
	public String getCharacterEncoding() {
		String characterEncoding =this.getRequest().getCharacterEncoding();
		return StringUtils.isBlank(characterEncoding)?"utf-8":characterEncoding;
	}
}

 最后，测试了下，确实解决了使用undertow作为web容器带来的中文乱码的问题。