Spring Boot整合jsp後必須經過spring-boot:run方式啓動？
爲何整合jsp後必須經過spring-boot:run方式啓動？
背景
在Spring Boot - 整合Jsp/FreeMarker這篇文章中，咱們用了兩種啓動方式java
- mvn clean spring-boot:run
- main方法啓動
測試發現，經過maven啓動可以正常渲染jsp頁面，而經過main方法啓動沒法渲染，本文分析下緣由。
分析
咱們代碼沒有調整，只是啓動方式不一樣，那麼懷疑是classpath不一致！web
- mvn啓動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啓動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
- 對比
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
對比後發現，經過main啓動後classpath缺乏tomcat-embed-jasper.jar；定位到這裏，咱們就能夠解決這個問題了。spring
- 解決方法：去掉將pom.xml中tomcat-embed-jasper依賴<scope>provided</scope>，依賴調整以下
<dependency>
<groupId>org.apache.tomcat.embed</groupId>
<artifactId>tomcat-embed-jasper</artifactId>
<!--
<scope>provided</scope>
-->
</dependency>
還原現場，分析Spring Boot啓動流程
在IDE裏，直接運行的main函數：express
@SpringBootApplication
public class Start {
public static void main(String[] args) {
SpringApplication.run(Start.class, args);
}
}
Embead Tomcat的Servlet加載流程
- 判斷是否在web環境，略，你們本身查閱相關資料，不是本文重點。
- spring boot經過TomcatEmbeddedServletContainerFactory來啓動對應的web服務器。
//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，加載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());
}
……
}
// 判斷是否加載jspServlet
protected boolean shouldRegisterJspServlet() {
return this.jspServlet != null && this.jspServlet.getRegistered() && ClassUtils
.isPresent(this.jspServlet.getClassName(), getClass().getClassLoader());
}
shouldRegisterJspServlet是重點了，這裏ClassUtils.isPresent會去classLoader裏面加載jspServlet（org.apache.jasper.servlet.JspServlet)，可是classpath裏面沒有這個類。addJspServlet沒有被執行apache
被吃掉的異常
繼續跟進（若是addJspServlet被執行）
jspServlet對象被添加到Tomcat上下文中，而且以jsp擴展名爲key放到HashMap中，接下來猜測，當有web請求會經過jsp擴展名去找到jspServlet對象，而後執行jsp。segmentfault
驗證
- 訪問http://localhost:8080/jsp/home，請求首先被tomcat容器攔截到，而後查找適合的servlet來處理（Tomcat自己是Servlet容器，經過servlet來響應請求，Spring也是經過註冊servlet到tomcat才能處理請求的，固然Jsp也就是servlet），咱們來看下核心類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();
// 經過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 {
// 不少匹配規則，這咱們關注 Extension Match （擴展名）
// 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) {
// 默認使用org.springframework.web.servlet.DispatcherServlet
mappingData.wrapper = contextVersion.defaultWrapper.object;
}}
}
咱們的請求path是：/jsp/home，因此沒有匹配Rule 3，而是使用默認servlet，那麼這個請求被spring的dispatcherServlet接管，而後執行controllerapi
@RequestMapping("/jsp/home")
public String home() {
return "home";
}
方法執行完畢，spring會去加載home這個view，因爲咱們整合了jsp，因此經過配置spring.mvc.view.prefix=/WEB-INF/jsp/ 這個路徑下，尋找home.jsp文件，而後將請求轉發（這裏你們須要瞭解一下，請求轉發和重定向的區別）到/WEB-INF/jsp/home.jsp。tomcat
- 處理jsp請求
請求（WEB-INF/jsp/home.jsp）被Tomcat再次攔截，匹配Rule 3，經過擴展名jsp，在map中獲取到jspServlet對象，給你們截圖
總結
簡單總結一下，本文闡述的問題並非平常開發中的主要問題（可能連主要問題都算不上，誰會用main去調試？？），可是遇到了就花時間來研究一下，仍是有所收穫的。springboot
- 分析問題思路
- Spring Boot 初始化的部分流程
- 請求轉發和重定向的區別
另外你們注意若是pom文件中<scope>去掉，再正常部署到tomcat容器中，會有jar衝突，建議你們試驗事後，修改回去。服務器
最後
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