Failure when deploying Spring App to Heroku - spring

Question

I am trying to deploy my spring application to heroku but there is some error in maven plugins I believe. Have tried every possible version combination, things worked locally but not when deploying.
When i'm running :
git push heroku master
Following is the error:
pom.xml
<?xml version="1.0" encoding="UTF-8"?>
4.0.0
org.springframework.boot
spring-boot-starter-parent
2.3.3.RELEASE
com.project
techupdate
0.0.1-SNAPSHOT
techupdate
Demo project for Spring Boot
<properties>
<java.version>1.8</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>com.h2database</groupId>
<artifactId>h2</artifactId>
<scope>runtime</scope>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
<exclusions>
<exclusion>
<groupId>org.junit.vintage</groupId>
<artifactId>junit-vintage-engine</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>org.springframework.security</groupId>
<artifactId>spring-security-test</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-security</artifactId>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
</dependency>
<dependency>
<groupId>com.auth0</groupId>
<artifactId>java-jwt</artifactId>
<version>3.4.0</version>
</dependency>
<!-- https://mvnrepository.com/artifact/com.google.code.gson/gson -->
<dependency>
<groupId>com.google.code.gson</groupId>
<artifactId>gson</artifactId>
<version>2.8.5</version>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-surefire-plugin</artifactId>
<version>2.19.1</version>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>9</source>
<target>9</target>
</configuration>
</plugin>
<plugin>
<artifactId>maven-dependency-plugin</artifactId>
</plugin>
</plugins>
</build>

Answer 1

Java 9 is not supported by Heroku, you can choose between 1.7, 1.8, 11, 13, 15 and 16, where 1.8 is the default. See Heroku Supported Java Versions.
If you do not want to use the default 1.8 you can change the Java version placing a file called system.properties in the project root setting the desired JDK:
java.runtime.version=16