java - Spring Boot Maven 不会构建可执行 Jar，因为它发现重复项

Question

因此，我尝试运行 mvn clean package 为我的 Spring Boot 应用程序构建可执行 jar，但它失败了，因为它发现了重复项。

以下是出现的错误消息的示例。其中大部分似乎与 Tomcat 相关:

[WARNING] Found duplicate (but equal) classes in [org.apache.tomcat.embed:tomcat-embed-core:8.5.20, org.apache.tomcat:tomcat-juli:8.5.20]:

这些重复项从哪里来？和我的pom.xml有什么关系吗？

<?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>
    <!-- Output to jar format -->
    <packaging>jar</packaging>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starters</artifactId>
        <version>1.5.7.RELEASE</version>
    </parent>
    <artifactId>spring-boot-starter-web</artifactId>
    <name>Spring Boot Web Starter</name>
    <description>Starter for building web, including RESTful, applications using Spring
        MVC. Uses Tomcat as the default embedded container
    </description>
    <url>http://projects.spring.io/spring-boot/</url>
    <organization>
        <name>Pivotal Software, Inc.</name>
        <url>http://www.spring.io</url>
    </organization>
    <properties>
        <main.basedir>${basedir}/../..</main.basedir>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-tomcat</artifactId>
        </dependency>
        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-validator</artifactId>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-webmvc</artifactId>
        </dependency>
        <!-- JPA Data (for using Repositories, Entities, Hibernate, etc...) -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <!-- Use MySQL Connector-J -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
            <version>1.5.7.RELEASE</version>
            <scope>test</scope>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>com.h2database</groupId>
            <artifactId>h2</artifactId>
            <version>1.4.194</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-thymeleaf</artifactId>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <executions>
                    <execution>
                        <goals>
                            <goal>repackage</goal>
                        </goals>
                        <configuration>
                            <classifier>spring-boot</classifier>
                                <mainClass>
                                    app.ContactRunner
                                </mainClass>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
        <testResources>
            <testResource>
                <directory>src/test/resources</directory>
            </testResource>
        </testResources>
    </build>

    <repositories>
        <repository>
            <id>spring-releases</id>
            <url>https://repo.spring.io/libs-release</url>
        </repository>
    </repositories>
    <pluginRepositories>
        <pluginRepository>
            <id>spring-releases</id>
            <url>https://repo.spring.io/libs-release</url>
        </pluginRepository>
    </pluginRepositories>
</project>

也许是因为我导入了太多入门项目或其他什么？真的只是不确定。

编辑

使用更完整的堆栈跟踪运行它，它说我没有定义任何目标，尽管我的 POM 显然有一个目标:

org.apache.maven.lifecycle.NoGoalSpecifiedException: No goals have been specified for this build. You must specify a valid lifecycle phase or a goal in the format : or :[:]:.

但我认为这是由于出现了所有重复的依赖关系。我看过一些关于删除它们的帖子，但它们都没有意义，因为依赖项会通过一些更大的、包罗万象的 <dependency> 自动进入。标签

例如，一个警告是这样说的:

[WARNING] Found duplicate and different classes in [org.apache.tomcat.embed:tomcat-embed-core:8.5.20, org.hibernate.javax.persistence:hibernate-jpa-2.1-api:1.0.0.Final]:
[WARNING]   javax.persistence.PersistenceContext
[WARNING]   javax.persistence.PersistenceContextType

我需要 tomcat 和 jpa 依赖项，并且我没有专门添加 PersistenceContext，它们会自动添加。如何防止依赖项重复或防止错误？

Answer 1

删除<scope>test</scope>来自此依赖项:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <version>1.5.7.RELEASE</version>
    <scope>test</scope>
</dependency>

删除这些依赖项:

<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-web</artifactId>
</dependency>
<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-webmvc</artifactId>
</dependency>

总而言之:依靠spring-boot-starter-* Artifact 为您提供正确的传递依赖项，而不是尝试添加(可能存在冲突的)单独的 Spring 依赖项。

更新 1 对此的回应:

when I get rid of those dependencies, it causes the @GetMapping or @ResponseBody annotations to not be found in the project

GetMapping和ResponseBody接口(interface)位于 org.springframework:spring-web这是通过 org.springframework.boot:spring-boot-starter-web 提供的人工制品。所以，只要你去掉了<scope>test</scope>来自您的spring-boot-starter-web依赖，那么你就会拥有这些。尝试从命令行重建项目和/或在进行我建议的更改之后将其重新导入到 IDE 中。

您也可以删除此...

<dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-validator</artifactId>
</dependency>

...因为它是由 spring-boot-starter-web 提供的

并且，如果 h2是 mysql 的仅测试替代品那么你应该添加 <scope>test</scope>对此依赖项:

<dependency>
    <groupId>com.h2database</groupId>
    <artifactId>h2</artifactId>
    <version>1.4.194</version>
</dependency>

最后，我建议使用其中一个或两个教程以小规模、安全的方式尝试 Spring Boot 的这些方面:

• https://spring.io/guides/gs/accessing-data-jpa/
• https://spring.io/guides/gs/accessing-data-rest/