如果我们添加适当的jar引用，为什么Spring Boot不支持jsp却可以呈现页面，为什么它不支持jsp

Question

到处都写有Spring Boot不支持jsp视图。在其正式文件中有三个原因

• 对于Jetty和Tomcat，如果使用战争包装，它应该可以工作。与java -jar一起启动时，可执行的war将起作用，并且还将可部署到任何标准容器中。使用可执行jar时，不支持JSP。
• Undertow不支持JSP。
• 创建定制的error.jsp页面不会覆盖默认视图以进行错误处理。应改用自定义错误页面。

对于第一项，“使用可执行jar时不支持JSP”。但是，当我添加对tomcat-embed-jasper的引用并在application.properties中设置正确的资源路径时，jsp文件也可以很好地呈现。

我想这可能意味着如果不调用其他参考库（例如tomcat-embed-jasper），Spring Boot将不支持jsp。

但是对于百里香，我们还必须导入spring-boot-starter-thymeleaf。为什么我们可以说Spring Boot通过附加的库来支持thymleaf。

那么我如何理解文档中的第一项呢？

Answer 1

Embedded Tomcat package (which is used in springboot to create executable jar)does not include JSP by default, we must add the module “org.apache.tomcat.embed:tomcat-embed-jasper” as well.That is the reason why we are adding tomcat-embed-jasper as dependency in springboot, so that we can use the jstl tags in jsp.

The main reason why springboot does not work properly with jsp as view resolver , when *jar is used as packaging is because of a hard coded file pattern in Tomcat.The issue is that when you are using java -*.jar to deploy a springboot application , the jsp files will not be present in the embedded tomcat and while trying to serve the request you will get a 404 PAGE NOT FOUND. This is because of the jar packaging ,that the jsp files are not getting copied from the WEB-INF folder.If you keep the jsp files under the META-INF/resources folder while using jar as packaging it should work.

Thymeleaf allows using templates as prototypes, meaning they can be viewed as static files and put in resources/templates folder for spring to pick up.But jsp files will have jstl tags etc which needs to be transpiled by the jasper before rendering , so they cannot be set as static files according to my knowledge.

When using a WAR(Webapplication archive), the packing will automatically take the resources from the following project structure :

 |-- pom.xml
 `-- src
     `-- main
         |-- java
         |   `-- com
         |       `-- example
         |           `-- projects
         |               `-- SampleAction.java
         |-- resources
         |   `-- images
         |       `-- sampleimage.jpg
         `-- webapp
             |-- WEB-INF
             |   `-- web.xml
             |-- index.jsp
             `-- jsp
                 `-- websource.jsp

Guides and official sample for using springboot with jsp : Guide , Sample Repo

The WAR packaging structure insists on keeping jsp files under webapp/ folder and it will work as expected. The maven war goal will copy the files from the webapp folder to the WEB-INF and all resource files like jsp will be at the root of the war packaging.From here, the maven-repackage goal or spring boot repackaging takes care of making the jar/war executable.So, if the files are present in the orginal war , it will be in the executable one as well.The springboot executable war structure is as follows :

example.war
 |
 +-META-INF
 |  +-MANIFEST.MF
 +-org
 |  +-springframework
 |     +-boot
 |        +-loader
 |           +-<spring boot loader classes>
 +-WEB-INF
    +-classes
    |  +-com
    |     +-mycompany
    |        +-project
    |           +-YourClasses.class
    +-lib
    |  +-dependency1.jar
    |  +-dependency2.jar
    +-lib-provided
       +-servlet-api.jar
       +-dependency3.jar

So for the comment :

If you put your jsp files in the folder src/main/resources , anything that is put in this directory will be automatically copied to the WEB-INF/classes as per the WAR documentation.

So , if you keep your jsp files under src/main/resources and configure the following in yml or property file, it should work for WAR archives.I haven't tried it so not sure.

spring.mvc.view.prefix = /WEB-INF/classes/templates
spring.mvc.view.suffix = .jsp