【maven】maven聚合工程如何打包 解决maven pom.xml各种报错问题 规范pom文件

导入别人项目或者自己搭建项目时，每次必不可少都会遇到maven报错问题 （当然有可能是别人的项目pom写的不规范 自信点可能不是你的问题 但我们需要学会解决）。 这些问题 百度都不知道怎么查，最近着手自己搭建了一个springcloud聚合工程的demo 应该算是比较有代表性了,当然 springboot也可差不多 主要是理解maven的使用, 终于把这些给理解了个大概。文章有点长 原创不易

项目结构介绍： MySpringCloud为父模块，本文以红框内的模块举例， file为业务模块 调用了user-api工具模块，user-api引入了framework工具模块，两个工具模块被common模块管理

本文从多个层面分析maven综合报错问题：

1. 首先一个比较低级的错误 一般有了开发经验不会犯 但是入门者可能会踩坑 要确保maven配置里面的maven仓库地址是可用的，典型错误：早期maven中央仓库是http传输的，后来改成了https, 网上可能还存在很多错误的mirrors配置 换句话说 仓库地址都是错误的 所以会导致所有依赖下载失败，此外 不同的仓库地址 某些依赖的groupId有可能会不同

2. 确保了地址是可用的 groupId 和 artifactId都是无误:

   maven遇到的主要错误 应该属以下几个

   .A  Cannot resolve xxxx 错误 
   .B  Could not find artifact 错误
   .C  must be "pom" but is "jar"错误
   .D  程序包XXX 不存在
   .E Unable to find main class
   

解决方式：

1. 低级错误1：找到本地maven仓库路径 查找 .lastUpdated 结尾的文件 全部删除 ，出现这种文件的情况可能由于网络不好，下载错误 并且它会阻止下次下载；
2. 低级错误2：如果网络正常 且每次下载都是这个文件，那么很可能就是依赖版本号不正确，远程仓库根本没有这个包,所以一直都是 lastUpdated 。
   
3. 正文开始 用一个父子多模块maven项目 pom.xml文件实际举例 重点都在注释上面，顺便写了个英文版注释，因为xml比较容易乱码，项目几经周转很可能注释就乱了，这些注释就不复制出来了 研究这玩意 我累了。

父pom

<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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0modelVersion>
    <parent>
        <groupId>org.springframework.bootgroupId>
        <artifactId>spring-boot-starter-parentartifactId>
        <version>2.3.4.RELEASEversion>
        <relativePath/> 
    parent>
    
    <packaging>pompackaging>
    <groupId>com.demogroupId>
    <artifactId>MySpringCloudartifactId>
    <version>0.0.1-SNAPSHOTversion>
    <name>MySpringCloudname>
    <description>Demo project for Spring Bootdescription>

    
    <properties>
        <java.version>1.8java.version>
        <project.build.sourceEncoding>UTF-8project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8project.reporting.outputEncoding>

        <spring-cloud.version>Hoxton.SR8spring-cloud.version>
        <spring-cloud-alibaba.version>2.2.1.RELEASEspring-cloud-alibaba.version>

        <nacos.version>1.3.0nacos.version>
        <sentinel.version>1.8.2sentinel.version>
        <openfeign.version>2.2.5.RELEASEopenfeign.version>
        <netflix-hystrix.version>2.2.5.RELEASEnetflix-hystrix.version>

        <fastjson.version>1.2.76fastjson.version>
        <servlet.version>4.0.1servlet.version>
    properties>

    
    
    

    
    
    <dependencyManagement>

        <dependencies>
           
            
            <dependency>
                <groupId>org.springframework.cloudgroupId>
                <artifactId>spring-cloud-dependenciesartifactId>
                <version>${spring-cloud.version}version>
                
                
                <type>pomtype>
            dependency>

            
            <dependency>
                <groupId>com.alibaba.cloudgroupId>
                <artifactId>spring-cloud-alibaba-dependenciesartifactId>
                <version>${spring-cloud-alibaba.version}version>
                <type>pomtype>
                
                
                
                
                <scope>importscope>
            dependency>



            
            <dependency>
                <groupId>org.projectlombokgroupId>
                <artifactId>lombokartifactId>
                <optional>trueoptional>
                <version>${lombok.version}version>
            dependency>

            
            <dependency>
                <groupId>com.alibabagroupId>
                <artifactId>fastjsonartifactId>
                <version>${fastjson.version}version>
            dependency>

            
            <dependency>
                <groupId>com.alibaba.nacosgroupId>
                <artifactId>nacos-clientartifactId>
                <version>${nacos.version}version>
            dependency>


            
            <dependency>
                <groupId>com.alibaba.cspgroupId>
                <artifactId>sentinel-coreartifactId>
                <version>${sentinel.version}version>
            dependency>

            
            <dependency>
                <groupId>com.alibaba.cspgroupId>
                <artifactId>sentinel-transport-simple-httpartifactId>
                <version>${sentinel.version}version>
            dependency>

            
            <dependency>
                <groupId>org.springframework.cloudgroupId>
                <artifactId>spring-cloud-starter-openfeignartifactId>
                <version>${openfeign.version}version>
            dependency>

            
            <dependency>
                <groupId>org.springframework.cloudgroupId>
                <artifactId>spring-cloud-starter-netflix-hystrixartifactId>
                <version>${netflix-hystrix.version}version>
            dependency>

            
            <dependency>
                <groupId>javax.servletgroupId>
                <artifactId>javax.servlet-apiartifactId>
                <version>${servlet.version}version>
            dependency>
            
           
            <dependency>
                <groupId>org.apache.skywalkinggroupId>
                <artifactId>apm-toolkit-traceartifactId>
                
                <version>${skywalking.version}version>
            dependency>

            
            <dependency>
                <groupId>org.apache.skywalkinggroupId>
                <artifactId>apm-toolkit-logback-1.xartifactId>
                <version>${skywalking.version}version>
            dependency>

        dependencies>
    dependencyManagement>

    
    <modules>
        <module>commonmodule>
        <module>usermodule>
        <module>filemodule>
    modules>

	 


















project>

子pom

<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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0modelVersion>
    <parent>
        <groupId>com.demogroupId>
        <artifactId>MySpringCloudartifactId>
        <version>0.0.1-SNAPSHOTversion>
    parent>

    
    <packaging>jarpackaging>
    <groupId>com.qkjgroupId>
    <artifactId>fileartifactId>
    <version>0.0.1-SNAPSHOTversion>
    <name>filename>
    <description>Demo project for Spring Bootdescription>
    <properties>
        <java.version>1.8java.version>
    properties>
    <dependencies>

        
        <dependency>
            <groupId>org.springframework.bootgroupId>
            <artifactId>spring-boot-starter-webartifactId>
        dependency>

        <dependency>
            <groupId>org.springframework.cloudgroupId>
            <artifactId>spring-cloud-dependenciesartifactId>
            
            
            
            
            <version>${spring-cloud.version}version>
            <type>pomtype>
        dependency>

        
        <dependency>
            <groupId>com.alibaba.cloudgroupId>
            <artifactId>spring-cloud-alibaba-dependenciesartifactId>
            <version>${spring-cloud-alibaba.version}version>
            <type>pomtype>
        dependency>

        
        <dependency>
            <groupId>org.projectlombokgroupId>
            <artifactId>lombokartifactId>
            <optional>trueoptional>
        dependency>

        
        <dependency>
            <groupId>com.alibabagroupId>
            <artifactId>fastjsonartifactId>
            <version>${fastjson.version}version>
        dependency>

        
        <dependency>
            <groupId>com.alibaba.nacosgroupId>
            <artifactId>nacos-clientartifactId>
        dependency>

        
        <dependency>
            <groupId>com.alibaba.cspgroupId>
            <artifactId>sentinel-coreartifactId>
        dependency>

        
        <dependency>
            <groupId>com.alibaba.cspgroupId>
            <artifactId>sentinel-transport-simple-httpartifactId>
        dependency>

        
        <dependency>
            <groupId>org.springframework.cloudgroupId>
            <artifactId>spring-cloud-starter-openfeignartifactId>
        dependency>

        
        <dependency>
            <groupId>org.springframework.cloudgroupId>
            <artifactId>spring-cloud-starter-netflix-hystrixartifactId>
        dependency>


        
        
        
        <dependency>
            <groupId>com.alibaba.cloudgroupId>
            <artifactId>spring-cloud-starter-alibaba-nacos-discoveryartifactId>
        dependency>

        
        <dependency>
            <groupId>com.alibaba.cloudgroupId>
            <artifactId>spring-cloud-starter-alibaba-nacos-configartifactId>
        dependency>

        
        <dependency>
            <groupId>org.apache.skywalkinggroupId>
            <artifactId>apm-toolkit-traceartifactId>
        dependency>

        
        <dependency>
            <groupId>org.apache.skywalkinggroupId>
            <artifactId>apm-toolkit-logback-1.xartifactId>
        dependency>
        <dependency>
            <groupId>com.qkjgroupId>
            <artifactId>user-apiartifactId>
            <version>0.0.1-SNAPSHOTversion>
            
            
            <scope>compilescope>
        dependency>


    dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.bootgroupId>
                <artifactId>spring-boot-maven-pluginartifactId>
                <configuration>
                    <excludes>
                        <exclude>
                            <groupId>org.projectlombokgroupId>
                            <artifactId>lombokartifactId>
                        exclude>
                    excludes>
                configuration>
                <version>2.3.4.RELEASEversion>
            plugin>
        plugins>
    build>

project>

工具类父pom :common.pom

<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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0modelVersion>
    <parent>
        <groupId>com.demogroupId>
        <artifactId>MySpringCloudartifactId>
        <version>0.0.1-SNAPSHOTversion>
    parent>

    <packaging>pompackaging>

    <groupId>com.qkjgroupId>
    <artifactId>commonartifactId>
    <version>0.0.1-SNAPSHOTversion>
    <name>commonname>
    <description>Demo project for Spring Bootdescription>
    <properties>
        <java.version>1.8java.version>
    properties>

    <modules>
        <module>file-apimodule>
        <module>user-apimodule>
        <module>frameworkmodule>
    modules>


    
project>

工具类子pom : user-api.pom

<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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0modelVersion>
    <parent>
        <groupId>com.qkjgroupId>
        <artifactId>commonartifactId>
        <version>0.0.1-SNAPSHOTversion>
    parent>

    <packaging>jarpackaging>
    <artifactId>user-apiartifactId>
    <version>0.0.1-SNAPSHOTversion>
    <name>user-apiname>

    <properties>
        <java.version>1.8java.version>
    properties>

    <dependencies>
        
        <dependency>
            <groupId>org.springframework.cloudgroupId>
            <artifactId>spring-cloud-starter-openfeignartifactId>
        dependency>


        <dependency>
            <groupId>org.springframework.bootgroupId>
            <artifactId>spring-boot-starterartifactId>
        dependency>

        <dependency>
            <groupId>com.qkjgroupId>
            <artifactId>frameworkartifactId>
            <version>0.0.1-SNAPSHOTversion>
            
            
            <scope>compilescope>

        dependency>

        
    dependencies>



project>

工具类子pom: framework.pom

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>com.qkj</groupId>
        <artifactId>common</artifactId>
        <version>0.0.1-SNAPSHOT</version>
    </parent>

    <packaging>jar</packaging>
    <artifactId>framework</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>framework</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <!--feign 依赖-->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-openfeign</artifactId>
        </dependency>

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

        <!-- servlet -->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
        </dependency>

    </dependencies>


</project>

什么时候可以不写version？

父pom dependencyManagement 里面声明了version, 而子pom继承了 父pom(parent 节点声明继承关系) ，子pom依赖不声明版本，则使用父pom依赖版本，这在多子模块项目中方便管理。 而整个pom不存在parent时，version是一定要写的，如果不写则会报错

type: 默认为jar 因为我们的是聚合工程，所以父模块要声明为pom,否则会报must be “pom” but is "jar"错误

总结：

1. maven仓库地址有误或下载缓慢 网络不好 （推荐使用阿里仓库）
2. 版本号错误 或缺少版本号
3. 多模块项目中未正确声明父模块groupId artifactId
4. pom工程中 未正确声明type
5. 父模块中声明了maven打包插件 而子模块含有工具类模块