Spring Boot整合jsp后必须通过spring-boot:run方式启动?

7

为什么整合jsp后必须通过spring-boot:run方式启动?

背景

Spring Boot - 整合Jsp/FreeMarker这篇文章中,我们用了两种启动方式

  1. mvn clean spring-boot:run
  2. main方法启动
    测试发现,通过maven启动能够正常渲染jsp页面,而通过main方法启动无法渲染,本文分析下原因。

分析

我们代码没有调整,只是启动方式不同,那么怀疑是classpath不一致!

  • mvn启动classpath
/Users/wanye/Code/springboot/target/classes/
/Users/wanye/.m2/repository/ch/qos/logback/logback-classic/1.1.9/logback-classic-1.1.9.jar
/Users/wanye/.m2/repository/ch/qos/logback/logback-core/1.1.9/logback-core-1.1.9.jar
/Users/wanye/.m2/repository/com/fasterxml/classmate/1.3.3/classmate-1.3.3.jar
/Users/wanye/.m2/repository/com/fasterxml/jackson/core/jackson-annotations/2.8.0/jackson-annotations-2.8.0.jar
/Users/wanye/.m2/repository/com/fasterxml/jackson/core/jackson-core/2.8.6/jackson-core-2.8.6.jar
/Users/wanye/.m2/repository/com/fasterxml/jackson/core/jackson-databind/2.8.6/jackson-databind-2.8.6.jar
/Users/wanye/.m2/repository/javax/servlet/jstl/1.2/jstl-1.2.jar
/Users/wanye/.m2/repository/javax/validation/validation-api/1.1.0.Final/validation-api-1.1.0.Final.jar
/Users/wanye/.m2/repository/org/apache/tomcat/embed/tomcat-embed-core/8.5.11/tomcat-embed-core-8.5.11.jar
/Users/wanye/.m2/repository/org/apache/tomcat/embed/tomcat-embed-el/8.5.11/tomcat-embed-el-8.5.11.jar
/Users/wanye/.m2/repository/org/apache/tomcat/embed/tomcat-embed-jasper/8.5.11/tomcat-embed-jasper-8.5.11.jar
/Users/wanye/.m2/repository/org/apache/tomcat/embed/tomcat-embed-websocket/8.5.11/tomcat-embed-websocket-8.5.11.jar
/Users/wanye/.m2/repository/org/hibernate/hibernate-validator/5.3.4.Final/hibernate-validator-5.3.4.Final.jar
/Users/wanye/.m2/repository/org/jboss/logging/jboss-logging/3.3.0.Final/jboss-logging-3.3.0.Final.jar
/Users/wanye/.m2/repository/org/slf4j/jcl-over-slf4j/1.7.22/jcl-over-slf4j-1.7.22.jar
/Users/wanye/.m2/repository/org/slf4j/jul-to-slf4j/1.7.22/jul-to-slf4j-1.7.22.jar
/Users/wanye/.m2/repository/org/slf4j/log4j-over-slf4j/1.7.22/log4j-over-slf4j-1.7.22.jar
/Users/wanye/.m2/repository/org/slf4j/slf4j-api/1.7.22/slf4j-api-1.7.22.jar
/Users/wanye/.m2/repository/org/springframework/boot/spring-boot-autoconfigure/1.5.1.RELEASE/spring-boot-autoconfigure-1.5.1.RELEASE.jar
/Users/wanye/.m2/repository/org/springframework/boot/spring-boot-starter-logging/1.5.1.RELEASE/spring-boot-starter-logging-1.5.1.RELEASE.jar
/Users/wanye/.m2/repository/org/springframework/boot/spring-boot-starter-tomcat/1.5.1.RELEASE/spring-boot-starter-tomcat-1.5.1.RELEASE.jar
/Users/wanye/.m2/repository/org/springframework/boot/spring-boot-starter-web/1.5.1.RELEASE/spring-boot-starter-web-1.5.1.RELEASE.jar
/Users/wanye/.m2/repository/org/springframework/boot/spring-boot-starter/1.5.1.RELEASE/spring-boot-starter-1.5.1.RELEASE.jar
/Users/wanye/.m2/repository/org/springframework/boot/spring-boot/1.5.1.RELEASE/spring-boot-1.5.1.RELEASE.jar
/Users/wanye/.m2/repository/org/springframework/spring-aop/4.3.6.RELEASE/spring-aop-4.3.6.RELEASE.jar
/Users/wanye/.m2/repository/org/springframework/spring-beans/4.3.6.RELEASE/spring-beans-4.3.6.RELEASE.jar
/Users/wanye/.m2/repository/org/springframework/spring-context/4.3.6.RELEASE/spring-context-4.3.6.RELEASE.jar
/Users/wanye/.m2/repository/org/springframework/spring-core/4.3.6.RELEASE/spring-core-4.3.6.RELEASE.jar
/Users/wanye/.m2/repository/org/springframework/spring-expression/4.3.6.RELEASE/spring-expression-4.3.6.RELEASE.jar
/Users/wanye/.m2/repository/org/springframework/spring-web/4.3.6.RELEASE/spring-web-4.3.6.RELEASE.jar
/Users/wanye/.m2/repository/org/springframework/spring-webmvc/4.3.6.RELEASE/spring-webmvc-4.3.6.RELEASE.jar
/Users/wanye/.m2/repository/org/yaml/snakeyaml/1.17/snakeyaml-1.17.jar
  • Main启动classpath
/Users/wanye/Code/springboot/target/classes/
/Users/wanye/.m2/repository/ch/qos/logback/logback-classic/1.1.9/logback-classic-1.1.9.jar
/Users/wanye/.m2/repository/ch/qos/logback/logback-core/1.1.9/logback-core-1.1.9.jar
/Users/wanye/.m2/repository/com/fasterxml/classmate/1.3.3/classmate-1.3.3.jar
/Users/wanye/.m2/repository/com/fasterxml/jackson/core/jackson-annotations/2.8.0/jackson-annotations-2.8.0.jar
/Users/wanye/.m2/repository/com/fasterxml/jackson/core/jackson-core/2.8.6/jackson-core-2.8.6.jar
/Users/wanye/.m2/repository/com/fasterxml/jackson/core/jackson-databind/2.8.6/jackson-databind-2.8.6.jar
/Users/wanye/.m2/repository/javax/servlet/jstl/1.2/jstl-1.2.jar
/Users/wanye/.m2/repository/javax/validation/validation-api/1.1.0.Final/validation-api-1.1.0.Final.jar
/Users/wanye/.m2/repository/org/apache/tomcat/embed/tomcat-embed-core/8.5.11/tomcat-embed-core-8.5.11.jar
/Users/wanye/.m2/repository/org/apache/tomcat/embed/tomcat-embed-el/8.5.11/tomcat-embed-el-8.5.11.jar
/Users/wanye/.m2/repository/org/apache/tomcat/embed/tomcat-embed-websocket/8.5.11/tomcat-embed-websocket-8.5.11.jar
/Users/wanye/.m2/repository/org/hibernate/hibernate-validator/5.3.4.Final/hibernate-validator-5.3.4.Final.jar
/Users/wanye/.m2/repository/org/jboss/logging/jboss-logging/3.3.0.Final/jboss-logging-3.3.0.Final.jar
/Users/wanye/.m2/repository/org/slf4j/jcl-over-slf4j/1.7.22/jcl-over-slf4j-1.7.22.jar
/Users/wanye/.m2/repository/org/slf4j/jul-to-slf4j/1.7.22/jul-to-slf4j-1.7.22.jar
/Users/wanye/.m2/repository/org/slf4j/log4j-over-slf4j/1.7.22/log4j-over-slf4j-1.7.22.jar
/Users/wanye/.m2/repository/org/slf4j/slf4j-api/1.7.22/slf4j-api-1.7.22.jar
/Users/wanye/.m2/repository/org/springframework/boot/spring-boot-autoconfigure/1.5.1.RELEASE/spring-boot-autoconfigure-1.5.1.RELEASE.jar
/Users/wanye/.m2/repository/org/springframework/boot/spring-boot-starter-logging/1.5.1.RELEASE/spring-boot-starter-logging-1.5.1.RELEASE.jar
/Users/wanye/.m2/repository/org/springframework/boot/spring-boot-starter-tomcat/1.5.1.RELEASE/spring-boot-starter-tomcat-1.5.1.RELEASE.jar
/Users/wanye/.m2/repository/org/springframework/boot/spring-boot-starter-web/1.5.1.RELEASE/spring-boot-starter-web-1.5.1.RELEASE.jar
/Users/wanye/.m2/repository/org/springframework/boot/spring-boot-starter/1.5.1.RELEASE/spring-boot-starter-1.5.1.RELEASE.jar
/Users/wanye/.m2/repository/org/springframework/boot/spring-boot/1.5.1.RELEASE/spring-boot-1.5.1.RELEASE.jar
/Users/wanye/.m2/repository/org/springframework/spring-aop/4.3.6.RELEASE/spring-aop-4.3.6.RELEASE.jar
/Users/wanye/.m2/repository/org/springframework/spring-beans/4.3.6.RELEASE/spring-beans-4.3.6.RELEASE.jar
/Users/wanye/.m2/repository/org/springframework/spring-context/4.3.6.RELEASE/spring-context-4.3.6.RELEASE.jar
/Users/wanye/.m2/repository/org/springframework/spring-core/4.3.6.RELEASE/spring-core-4.3.6.RELEASE.jar
/Users/wanye/.m2/repository/org/springframework/spring-expression/4.3.6.RELEASE/spring-expression-4.3.6.RELEASE.jar
/Users/wanye/.m2/repository/org/springframework/spring-web/4.3.6.RELEASE/spring-web-4.3.6.RELEASE.jar
/Users/wanye/.m2/repository/org/springframework/spring-webmvc/4.3.6.RELEASE/spring-webmvc-4.3.6.RELEASE.jar
/Users/wanye/.m2/repository/org/yaml/snakeyaml/1.17/snakeyaml-1.17.jar
  • 对比
192:~ wanye$ diff Desktop/mainsort Desktop/mvnsort
12a13
> /Users/wanye/.m2/repository/org/apache/tomcat/embed/tomcat-embed-jasper/8.5.11/tomcat-embed-jasper-8.5.11.jar

对比后发现,通过main启动后classpath缺少tomcat-embed-jasper.jar;定位到这里,我们就可以解决这个问题了。

  • 解决方法:去掉将pom.xml中tomcat-embed-jasper依赖<scope>provided</scope>,依赖调整如下
<dependency>
    <groupId>org.apache.tomcat.embed</groupId>
    <artifactId>tomcat-embed-jasper</artifactId>
    <!--
    <scope>provided</scope>
    -->
</dependency>

还原现场,分析Spring Boot启动流程

在IDE里,直接运行的main函数:

@SpringBootApplication
public class Start {
    public static void main(String[] args) {
        SpringApplication.run(Start.class, args);
    }
}

Embead Tomcat的Servlet加载流程

  1. 判断是否在web环境,略,大家自己查阅相关资料,不是本文重点。
  2. spring boot通过TomcatEmbeddedServletContainerFactory来启动对应的web服务器。
//TomcatEmbeddedServletContainerFactory
    @Override
    public EmbeddedServletContainer getEmbeddedServletContainer(
            ServletContextInitializer... initializers) {
        Tomcat tomcat = new Tomcat();
        File baseDir = (this.baseDirectory != null ? this.baseDirectory
                : createTempDir("tomcat"));
        tomcat.setBaseDir(baseDir.getAbsolutePath());
        Connector connector = new Connector(this.protocol);
        tomcat.getService().addConnector(connector);
        customizeConnector(connector);
        tomcat.setConnector(connector);
        tomcat.getHost().setAutoDeploy(false);
        configureEngine(tomcat.getEngine());
        for (Connector additionalConnector : this.additionalTomcatConnectors) {
            tomcat.getService().addConnector(additionalConnector);
        }
        // 初始化上下文,加载Servlet
        prepareContext(tomcat.getHost(), initializers);
        return getTomcatEmbeddedServletContainer(tomcat);
    }

初始化Servlet

protected void prepareContext(Host host, ServletContextInitializer[] initializers) {
    ……
    if (isRegisterDefaultServlet()) {
        addDefaultServlet(context);
    }
    // 初始化JspServlet
    if (shouldRegisterJspServlet()) {
        addJspServlet(context);
        addJasperInitializer(context);
        context.addLifecycleListener(new StoreMergedWebXmlListener());
    }
    ……
}
// 判断是否加载jspServlet
protected boolean shouldRegisterJspServlet() {
    return this.jspServlet != null && this.jspServlet.getRegistered() && ClassUtils
            .isPresent(this.jspServlet.getClassName(), getClass().getClassLoader());
}

shouldRegisterJspServlet是重点了,这里ClassUtils.isPresent会去classLoader里面加载jspServlet(org.apache.jasper.servlet.JspServlet),但是classpath里面没有这个类。addJspServlet没有被执行

被吃掉的异常

图片描述

继续跟进(如果addJspServlet被执行)

图片描述

jspServlet对象被添加到Tomcat上下文中,并且以jsp扩展名为key放到HashMap中,接下来猜想,当有web请求会通过jsp扩展名去找到jspServlet对象,然后执行jsp。

验证

  • 访问http://localhost:8080/jsp/home,请求首先被tomcat容器拦截到,然后查找适合的servlet来处理(Tomcat本身是Servlet容器,通过servlet来响应请求,Spring也是通过注册servlet到tomcat才能处理请求的,当然Jsp也就是servlet),我们来看下核心类org.apache.catalina.mapper.Mapper
public void map(MessageBytes host, MessageBytes uri, String version,
                MappingData mappingData) throws IOException {

    if (host.isNull()) {
        host.getCharChunk().append(defaultHostName);
    }
    host.toChars();
    uri.toChars();
        // 通过uri,找servlet映射
    internalMap(host.getCharChunk(), uri.getCharChunk(), version,
            mappingData);
}
// 匹配servlet的核心方法
private final void internalMapWrapper(ContextVersion contextVersion,
                                      CharChunk path,
                                      MappingData mappingData) throws IOException {
      // 很多匹配规则,这我们关注 Extension Match (扩展名)
    // Rule 3 -- Extension Match
    MappedWrapper[] extensionWrappers = contextVersion.extensionWrappers;
    if (mappingData.wrapper == null && !checkJspWelcomeFiles) {
        internalMapExtensionWrapper(extensionWrappers, path, mappingData,
                true);
    }
    // Rule 7 -- Default servlet
    if (mappingData.wrapper == null && !checkJspWelcomeFiles) {
        if (contextVersion.defaultWrapper != null) {
              // 默认使用org.springframework.web.servlet.DispatcherServlet
            mappingData.wrapper = contextVersion.defaultWrapper.object;
     }}
}

我们的请求path是:/jsp/home,所以没有匹配Rule 3,而是使用默认servlet,那么这个请求被spring的dispatcherServlet接管,然后执行controller

@RequestMapping("/jsp/home")
public String home() {
    return "home";
}

方法执行完毕,spring会去加载home这个view,由于我们整合了jsp,所以通过配置spring.mvc.view.prefix=/WEB-INF/jsp/ 这个路径下,寻找home.jsp文件,然后将请求转发(这里大家需要了解一下,请求转发和重定向的区别)到/WEB-INF/jsp/home.jsp。

  • 处理jsp请求
    请求(WEB-INF/jsp/home.jsp)被Tomcat再次拦截,匹配Rule 3,通过扩展名jsp,在map中获取到jspServlet对象,给大家截图

图片描述

总结

简单总结一下,本文阐述的问题并不是日常开发中的主要问题(可能连主要问题都算不上,谁会用main去调试??),但是遇到了就花时间来研究一下,还是有所收获的。

  1. 分析问题思路
  2. Spring Boot 初始化的部分流程
  3. 请求转发和重定向的区别

另外大家注意如果pom文件中<scope>去掉,再正常部署到tomcat容器中,会有jar冲突,建议大家试验过后,修改回去。

最后

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图片描述

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taolive · 2017年08月18日

测试了好多次,现在发现是这样的:

  1. 如果main 方法所在的项目是maven顶级项目,则用main方法运行,可以访问jsp

  2. 如果main方法所在的项目是maven的子模块项目(如 Main-Parent项目中,包含maven-A子模块,正好main方法就在maven-A 模块中)则main方法运行,无法访问jsp

+1 回复

0

你说的对,我卡在这好久,总404... 那你解决这个问题了吗

star_sky · 2018年05月08日
taolive · 2017年08月16日

作者确定是从main方法启动?我根据你的操作,从main方法启动,jsp还是不能访问,但是spring-boot:run 则可以访问jsp

回复

0

确定,看看pom是不是漏了,重新编译一下

刘忠旭 作者 · 2017年08月16日
1

@万夜 能否把你的用例放到git上,分享出来呢?我确定pom.xml都有了呀

taolive · 2017年08月16日
0

@taolive 代码没保留。多尝试一下,肯定可以的

刘忠旭 作者 · 2017年08月17日
moonbow · 2月27日

刘老师,您好,请问如何查看两种方式时的classpath。

回复

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