Unable to start local HTTP API before maven test execution

I've developed an HTTP API which I'm trying to test using Maven. Example test looks like this:

@Test
public void firstExampleTest() {
    RestAssured.port = 8080;
    RestAssured.baseURI = "http://127.0.0.1";
    given().
    when().
        get("/something").
    then().
        statusCode(404);
}

When executed, it throws firstExampleTest(my.app.AppTest): Connection refused: connect. It works fine when I run API manually first using mvn exec:java. I've added exec-maven-plugin to my POM.xml, but still no luck. How can I run the API first before executing tests? My POM.xml file:

<?xml version="1.0" encoding="UTF-8"?>

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>my.app</groupId>
  <artifactId>my-app</artifactId>
  <version>1.0-SNAPSHOT</version>

  <name>my-app</name>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <maven.compiler.source>1.7</maven.compiler.source>
    <maven.compiler.target>1.7</maven.compiler.target>
  </properties>

  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.11</version>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>org.json</groupId>
      <artifactId>json</artifactId>
      <version>20180813</version>
    </dependency>
    <dependency>
      <groupId>io.rest-assured</groupId>
      <artifactId>rest-assured</artifactId>
      <version>3.3.0</version>
      <scope>test</scope>
    </dependency>
  </dependencies>

  <build>
    <pluginManagement>
      <plugins>
        <plugin>
          <groupId>org.codehaus.mojo</groupId>
          <artifactId>exec-maven-plugin</artifactId>
          <version>1.4.0</version>
          <executions>
            <execution>
              <phase>generate-test-resources</phase>
              <goals>
                <goal>exec</goal>
              </goals>
            </execution>
          </executions>
          <configuration>
            <mainClass>my.app.App</mainClass>
          </configuration>
        </plugin>
      </plugins>
    </pluginManagement>
  </build>
</project>