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Spring boot doesn't identify html templates without Thymeleaf dependency

I am using spring-boot 2.5.0 and maven as dependency management tool. I have following dependencies as of now in my project.
"<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<optional>true</optional>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>"
I want to use jsp instead of thymeleaf but when I put my "index.html" file inside templates or static sub-folder of resources folder it doesn't recognize the html file and throws white label error.When I added the thymeleaf dependency it worked perfectly and recognized the html file. So, what should I do to make spring-boot detect my html file without adding thymeleaf dependency. By the way I have never used jsp before.

It seems you are missing either of the two things.
you should put below the property with the desired value in the property/yaml file
spring.mvc.view.prefix: <location of html/jsp>
spring.mvc.view.suffix: <.extension>
check at your controller whether you are sending the correct view name or not.

Spring boot application stuck when adding jnpclient maven dependency

I need to load a JNDI resource located in a JBoss server. For this, I am using a jnp-client library:
<dependency>
<groupId>jboss</groupId>
<artifactId>jnp-client</artifactId>
<version>4.2.2.GA</version>
</dependency>
The problem is that as soon as I include this dependency in my pom.xml, the Spring application gets stuck at the start time without any message. Not a single line of logs, like if it is trying to load something forever. The main is not even invoked. Removing this dependency the application runs but I get an expected:
ClassNotFoundException: org.jnp.interfaces.NamingContextFactory
Which is normal because I have removed the dependency that includes this class.
Any clue?
I have tried all version of jnp-client or jbossall-client that also includes this NamingContextFactory
EDIT:
It is the mix of these two dependencies that unfortunately are inherited from required dependencies:
<dependency>
<groupId>org.jboss.naming</groupId>
<artifactId>jnp-client</artifactId>
</dependency>
and spring-webmvc inside
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
If I run with
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
<exclusions>
<exclusion>
<groupId>org.springframework</groupId>
<artifactId>spring-webmvc</artifactId>
</exclusion>
</exclusions>
</dependency>
It works fine.
Now, if I exclude the jnp-client I cannot access the JNDI resource, but if I remove the spring-security-web I cannot access the REST endopoints this service exposes.
EDIT2:
So I thought it could be two classes interfering with each other and I started the java process with -verbose. This is what I found.
org.springframework.boot.context.config.ConfigFileApplicationListener$Loader$$Lambda$165/0x00000001002d8440
source:
org.springframework.boot.context.config.ConfigFileApplicationListener$Loader
[389.020s][info][class,load]
org.springframework.boot.context.config.ConfigFileApplicationListener$Loader$$Lambda$166/0x00000001002d8840
source:
org.springframework.boot.context.config.ConfigFileApplicationListener$Loader
[558.011s][info][class,load]
org.springframework.boot.context.config.ConfigFileApplicationListener$Loader$$Lambda$167/0x00000001002d8c40
source:
org.springframework.boot.context.config.ConfigFileApplicationListener$Loader
[558.012s][info][class,load]
org.springframework.boot.context.config.ConfigFileApplicationListener$Loader$$Lambda$168/0x00000001002d9040
source:
org.springframework.boot.context.config.ConfigFileApplicationListener$Loader
From time to time the application prints, only in verbose, this ConfigFileApplicationListener$Loader
EDIT 3:
It seems that the problem is TimedSocketFactory inside the jnp-client. Somehow, just by having this class inside the jnp-client dependency, the Spring application is blocked and never starts. Removing this from the jnp-client allows the application to start. Of course, it fails later because the JNDI cannot connect to the server.

Change the version of the embedded tomcat using spring starter

The requirement is to use spring boot version 2.2.6.RELEASE however the tomcat version should be 9.0.37.
I tried to do it by excluding the tomcat starter from the spring-boot-starter-web depdendency like so :
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
<version>${spring-boot.version}</version>
<exclusions>
<exclusion>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-logging</artifactId>
</exclusion>
<exclusion>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-tomcat</artifactId>
</exclusion>
</exclusions>
</dependency>
And added the spring-boot-starter-tomcat separately which has the 9.0.37 tomcat version :
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-tomcat</artifactId>
<version>2.3.2.RELEASE</version>
</dependency>
However even after doing so the version is not override and the following gets used :
Mar 11 2020 09:31:38 UTC
Apache Tomcat/9.0.33
9.0.33.0
Do we need to do anything else to override the tomcat version?
Is it possible to override it by excluding started?
Update:
The parent pom is a corporate parent pom and not the spring-boot-starter-parent. As per one of the answers we can simply override the tomcat.version property however my effective pom doesn't show it.

If you're not inheriting from spring-boot-starter-parent I can only guess that you import spring-boot-dependencies in your dependencies management somewhere.
The documentation covers what you need to do to override the tomcat version. Each tomcat artifact should be listed with the overridden version, before you imports spring-boot-dependencies. The list of artifacts can be found in spring-boot-dependencies.
Using a different version of the starter is wrong (you can't mix two Spring Boot versions in the same app) and will have no effect since dependency management is in control anyway. In other words, you'll get spring-boot-starter-web version 2.3.2.RELEASE indeed but all the artefacts that it brings will be managed by the dependency management (the tomcat version defined by version 2.2.6.RELEASE).
In that particular case of yours, upgrading to 2.2.9.RELEASE could also be an option as it provides dependency management for the tomcat version that you need.

Well, this has been already answered.
For you, as you are using maven, you need to override the properties set in parent Spring pom.
<properties>
......
<tomcat.version>your_version</tomcat.version>
......
<properties>
For gradle, it is simple as
ext['tomcat.version'] = '8.5.34'
in your main build.gradle
Source: How to change embedded tomcat's version in existing spring boot app?

Maven - Do you need a main to use a project as a library?

I'm working on a project where I have a "core" and an "API" that are two separate maven projects.
Currently, I'm exporting the API in a jar using Eclipse and I'm linking it in maven like that :
<dependency>
<groupId>com.project.my</groupId>
<artifactId>project-api</artifactId>
<version>1.0.0</version>
<scope>system</scope>
<systemPath>${project.basedir}/src/main/resources/dependencies/project-api.jar</systemPath>
</dependency>
It's working properly and I can use the classes defined in my API.
But now I want to have a better workflow and I'm trying to install the API in my local maven repository and then link it normaly in the core :
<dependency>
<groupId>com.project.my</groupId>
<artifactId>project-api</artifactId>
<version>1.0.0</version>
</dependency>
But when I run maven clean install I'm getting the following error :
Execution default of goal org.springframework.boot:spring-boot-maven-plugin:1.3.3.RELEASE:repackage failed: Unable to find main class
And I indeed don't have a main in my API, since I don't need one.
Note that I use spring-boot for both projects, as I'm using some of their dependencies and it's easier to let them manage the versions (I only use the utility classes in the API).
So I'd like to know if I HAVE to have a main anyway, even if I don't ever use it, or if I'm doing something wrong trying to install my API in the local repository ?
Thanks :)

Thanks to Thilo's wise advices, I managed to get it working.
So what I did was removing all unused spring-boot references from my API project and only keeping the spring dependencies I needed, and I was then able to run mvn clean install properly.
Here's what I got rid of :
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-devtools</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter</artifactId>
</dependency>
and
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>1.3.3.RELEASE</version>
<relativePath/>
</parent>
I had to add the versions to some of the dependencies that were previously managed by spring-boot, but it's now working fine.

How to make thymeleaf spring security namespace available?

I've got a Spring Boot app. From what I understand a boot app will only need the dependency in the pom and all is great. Unfortunately, that's not the case and even when I overcomplicate my configuration it still doesn't work - I can't use the sec namespace in my pages.
In my page the first issue is the namespace URI:
I've tried every option available in the Intellij fix menu and can't get it.
I suppose the result of that issue is the fact that I can't use the sec namespace anywhere. The pictured example may indeed be an invalid use but I've used <div> as well which is straight from the Thymeleaf examples:
Many of the answers here and other sources are relying on xml configuration as well, which is of no use. Still, I've made Java-based beans based on those xml examples with no luck.
What steps are required to use spring security and thymeleaf integration in a spring boot app using only Java based configuration (if that)?
pom.xml
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-mail</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-security</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-thymeleaf</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.thymeleaf.extras</groupId>
<artifactId>thymeleaf-extras-springsecurity4</artifactId>
<version>2.1.2.RELEASE</version>
</dependency>
...
</dependencies>

I have encountered the same issue and for me it helped to define schema locations like this:
<html lang="en"
xmlns:th="http://www.thymeleaf.org"
xmlns:layout="http://www.ultraq.net.nz/thymeleaf/layout"
xmlns:sec="http://www.thymeleaf.org/thymeleaf-extras-springsecurity4"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.thymeleaf.org http://www.thymeleaf.org
http://www.ultraq.net.nz/thymeleaf/layout http://www.ultraq.net.nz/thymeleaf/layout
http://www.thymeleaf.org/thymeleaf-extras-springsecurity4 http://www.thymeleaf.org/thymeleaf-extras-springsecurity4">
...
This includes also additional dialects for layout and spring security 4 which you can remove if you are not using them.