Spring Boot causes WebAppContext error when deployed to GAE

Question

I'm building out a REST API for a personal project, using Spring Boot to do so, and deploying onto Google App Engine. The project compiles and runs locally with no issues, and I can deploy to GAE with no build errors. However, when I navigate to my URI after I deploy to GAE, a 404 is thrown with the following message:

No context on this server matched or handled this request.
Contexts known to this server are:
/ ---> o.e.j.w.WebAppContext@56ef9176{/,file:///var/lib/jetty/webapps/root/,UNAVAILABLE}{/root.war} [failed]

I have both a build.gradle and pom.xml file, and dependencies have to be declared in both, which I believe is the issue.

My pom.xml contains:

<dependencyManagement>
  <dependencies>
    <dependency>
      <!-- Import dependency management from Spring Boot -->
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-dependencies</artifactId>
      <version>2.0.1.RELEASE</version>
      <type>pom</type>
      <scope>import</scope>
    </dependency>
  </dependencies>
</dependencyManagement>

<dependencies>
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
  </dependency>
</dependencies>

My build.gradle contains:

plugins {
  id 'org.springframework.boot' version '2.0.1.RELEASE'
}
apply plugin: 'io.spring.dependency-management'
dependencies {
  compile 'org.springframework.boot:spring-boot-starter-web'
}

When I remove both of the spring boot dependencies from both, the error disappears.

Any ideas?

Answer 1

Figured it out myself in the end, but will leave this up for anyone else who stumbles across the same error.
As I found in the docs: if you're using a WAR as your deployable (instead of a .jar file) then you must also import spring-boot-starter-tomcat as a provided dependency.

My pom.xml now looks like:

<dependencyManagement>
  <dependencies>
    <dependency>
      <!-- Import dependency management from Spring Boot -->
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-dependencies</artifactId>
      <version>2.0.1.RELEASE</version>
      <type>pom</type>
      <scope>import</scope>
    </dependency>
  </dependencies>
</dependencyManagement>

<dependencies>
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
  </dependency>
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-tomcat</artifactId>
    <scope>provided</scope>
  </dependency>
</dependencies>

And my build.gradle now looks like:

plugins {
  id 'org.springframework.boot' version '2.0.1.RELEASE'
}
apply plugin: 'io.spring.dependency-management'
dependencies {
  compile 'org.springframework.boot:spring-boot-starter-web'
  providedRuntime 'org.springframework.boot:spring-boot-starter-tomcat'
}