【发布时间】：2019-09-13 08:24:57
【问题描述】：
我一直在研究部署在 Heroku 上的应用程序。我已经部署了几个星期，它运行良好，但前几天它开始出现错误：
错误：无法找到或加载主类 MainView
我认为这可能是由于最近的依赖项更改造成的，所以我将我的代码恢复了 2 周后，恢复到我确信可以正常工作的版本 - 但我得到了同样的错误。这可能是什么原因造成的？为什么 heroku 会停止看到我的 MainView 类？
我的过程文件：
web: java -cp target/classes/com/vaadin/app MainView
还有我的 pom.xml：
<?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>com.vaadin.app</groupId>
<artifactId>wonderapp</artifactId>
<name>Wonderapp</name>
<version>1.0-SNAPSHOT</version>
<packaging>war</packaging>
<properties>
<maven.compiler.source>1.8</maven.compiler.source>
<maven.compiler.target>1.8</maven.compiler.target>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<failOnMissingWebXml>false</failOnMissingWebXml>
<vaadin.version>13.0.5</vaadin.version>
</properties>
<repositories>
<!-- Maven central - reduces first-time build time -->
<repository>
<id>central</id>
<url>https://repo1.maven.org/maven2/</url>
<snapshots><enabled>false</enabled></snapshots>
</repository>
<!-- Repository used by many Vaadin add-ons -->
<repository>
<id>Vaadin Directory</id>
<url>http://maven.vaadin.com/vaadin-addons</url>
</repository>
<!-- Repository needed for prerelease versions of Vaadin -->
<repository>
<id>vaadin-prereleases</id>
<url>https://maven.vaadin.com/vaadin-prereleases</url>
</repository>
</repositories>
<!-- <plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-dependency-plugin</artifactId>
<version>2.4</version>
<executions>
<execution>
<id>copy-dependencies</id>
<phase>package</phase>
<goals><goal>copy-dependencies</goal></goals>
</execution>
</executions>
</plugin> -->
<pluginRepositories>
<!-- Maven central - reduces first-time build time -->
<pluginRepository>
<id>central</id>
<url>https://repo1.maven.org/maven2/</url>
<snapshots><enabled>false</enabled></snapshots>
</pluginRepository>
<!-- Repository needed for prerelease versions of Vaadin -->
<pluginRepository>
<id>vaadin-prereleases</id>
<url>https://maven.vaadin.com/vaadin-prereleases</url>
<snapshots><enabled>false</enabled></snapshots>
</pluginRepository>
</pluginRepositories>
<dependencyManagement>
<dependencies>
<dependency>
<groupId>com.vaadin</groupId>
<artifactId>vaadin-charts-flow</artifactId>
</dependency>
<!-- I added this -->
<dependency>
<groupId>com.heroku.sdk</groupId>
<artifactId>heroku-maven-plugin</artifactId>
<version>7.26.2</version>
</dependency>
<!-- I added this -->
<dependency>
<groupId>com.vaadin</groupId>
<artifactId>vaadin-bom</artifactId>
<type>pom</type>
<scope>import</scope>
<version>${vaadin.version}</version>
</dependency>
</dependencies>
</dependencyManagement>
<dependencies>
<dependency>
<groupId>com.vaadin</groupId>
<artifactId>vaadin-core</artifactId>
</dependency>
<!-- Added to provide logging output as Flow uses -->
<!-- the unbound SLF4J no-operation (NOP) logger implementation -->
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-simple</artifactId>
</dependency>
<!-- JavaFX depencdency -->
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>javax.servlet-api</artifactId>
<version>3.1.0</version>
<scope>provided</scope>
</dependency>
<!-- JavaFX depencdency -->
</dependencies>
<build>
<plugins>
<!-- Here for hopefully heroku to work -->
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-dependency-plugin</artifactId>
<version>2.4</version>
<executions>
<execution>
<id>copy-dependencies</id>
<phase>package</phase>
<goals><goal>copy-dependencies</goal></goals>
</execution>
</executions>
</plugin>
<!-- heroku maven plugin -->
<plugin>
<groupId>com.heroku.sdk</groupId>
<artifactId>heroku-maven-plugin</artifactId>
<version>7.26.2</version>
</plugin>
<!-- heroku maven plugin -->
<!-- Jetty plugin for easy testing without a server -->
<plugin>
<groupId>org.eclipse.jetty</groupId>
<artifactId>jetty-maven-plugin</artifactId>
<version>9.4.11.v20180605</version>
<configuration>
<scanIntervalSeconds>1</scanIntervalSeconds>
</configuration>
</plugin>
</plugins>
</build>
<profiles>
<profile>
<!-- Production mode can be activated with either property or profile -->
<id>production-mode</id>
<activation>
<property>
<name>vaadin.productionMode</name>
</property>
</activation>
<properties>
<vaadin.productionMode>true</vaadin.productionMode>
</properties>
<dependencies>
<dependency>
<groupId>com.vaadin</groupId>
<artifactId>flow-server-production-mode</artifactId>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>com.vaadin</groupId>
<artifactId>vaadin-maven-plugin</artifactId>
<version>${vaadin.version}</version>
<executions>
<execution>
<goals>
<goal>copy-production-files</goal>
<goal>package-for-production</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
</profile>
</profiles>
</project>
【问题讨论】：