Why maven sometimes can't resolve dependencies?-CodePudding

I have a multimodule Maven project where parent pom is as follows

<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>groupId</groupId>
    <artifactId>poc</artifactId>
    <packaging>pom</packaging>
    <version>1.0-SNAPSHOT</version>
    <description>Root Maven project</description>
    <modules>
         <module>Spring</module>
         <module>SpringBootLocalstack</module>
    </modules>
</project>

and Spring module pom is (without mention any version) :

<?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">
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.6.1</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <modelVersion>4.0.0</modelVersion>
    <artifactId>Spring</artifactId>
    <dependencies>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-beans</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-autoconfigure</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.data</groupId>
            <artifactId>spring-data-redis</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-redis</artifactId>
        </dependency>
        <dependency>
            <groupId>redis.clients</groupId>
            <artifactId>jedis</artifactId>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <artifactId>maven-dependency-plugin</artifactId>
                <version>3.2.0</version>
                <executions>
                    <execution>
                        <id>analyze</id>
                        <goals>
                            <goal>analyze-only</goal>
                        </goals>
                        <configuration>
                            <failOnWarning>true</failOnWarning>
                            <outputXML>true</outputXML>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
            <plugin>
                <groupId>org.codehaus.mojo</groupId>
                <artifactId>versions-maven-plugin</artifactId>
                <version>2.7</version>
                <configuration>
                    <excludes>
                        <exclude>org.apache.commons:commons-collections4</exclude>
                    </excludes>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

SpringBootLocalstack module pom is :

<?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">
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.6.1</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>SpringBootLocalstack</artifactId>

    <properties>
        <maven.compiler.source>11</maven.compiler.source>
        <maven.compiler.target>11</maven.compiler.target>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
        </dependency>
        <dependency>
            <groupId>com.amazonaws</groupId>
            <artifactId>aws-java-sdk-dynamodb</artifactId>
            <version>1.11.356</version>
        </dependency>
        <dependency>
            <groupId>com.amazonaws</groupId>
            <artifactId>aws-java-sdk-ssm</artifactId>
            <version>1.11.665</version>
            <scope>compile</scope>
        </dependency>
        <dependency>
            <groupId>io.awspring.cloud</groupId>
            <artifactId>spring-cloud-aws-messaging</artifactId>
            <version>2.3.0</version>
        </dependency>
        <dependency>
            <groupId>com.amazonaws</groupId>
            <artifactId>aws-java-sdk-core</artifactId>
            <version>1.11.356</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-messaging</artifactId>
            <version>5.2.19.RELEASE</version>
        </dependency>

        <dependency>
            <groupId>io.awspring.cloud</groupId>
            <artifactId>spring-cloud-starter-aws-messaging</artifactId>
            <version>2.3.0</version>
        </dependency>
        <dependency>
            <groupId>commons-io</groupId>
            <artifactId>commons-io</artifactId>
            <version>2.11.0</version>
        </dependency>

        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-to-slf4j</artifactId>
            <version>2.11.1</version>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.4</version>
        </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>junit</groupId>
            <artifactId>junit</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-autoconfigure</artifactId>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <artifactId>maven-dependency-plugin</artifactId>
                <version>2.8</version>
                <executions>
                    <execution>
                        <id>analyze</id>
                        <goals>
                            <goal>analyze-only</goal>
                        </goals>
                        <configuration>
                            <failOnWarning>true</failOnWarning>
                            <outputXML>true</outputXML>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
            <plugin>
                <groupId>org.asciidoctor</groupId>
                <artifactId>asciidoctor-maven-plugin</artifactId>
                <version>1.5.8</version>
                <executions>
                    <execution>
                        <id>generate-docs</id>
                        <phase>prepare-package</phase>
                        <goals>
                            <goal>process-asciidoc</goal>
                        </goals>
                        <configuration>
                            <backend>html</backend>
                            <doctype>book</doctype>
                        </configuration>
                    </execution>
                </executions>
                <dependencies>
                    <dependency>
                        <groupId>org.springframework.restdocs</groupId>
                        <artifactId>spring-restdocs-asciidoctor</artifactId>
                        <version>${spring-restdocs.version}</version>
                    </dependency>
                </dependencies>
            </plugin>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
            </plugin>
            <plugin>
                <groupId>org.codehaus.mojo</groupId>
                <artifactId>versions-maven-plugin</artifactId>
                <version>2.7</version>
                <configuration>
                    <excludes>
                        <exclude>org.apache.commons:commons-collections4</exclude>
                    </excludes>
                </configuration>
            </plugin>

        </plugins>
    </build>
</project>

For Spring Module, When I reload all maven projects from IntelliJ, it successfully resolve all dependencies but for SpringBootLocalstack if I remove "version" tag from pom file it failed to resolve, Example:

     <dependency>
            <groupId>com.amazonaws</groupId>
            <artifactId>aws-java-sdk-core</artifactId>
              </dependency>

I am getting:

Cannot resolve com.amazonaws:aws-java-sdk-core:unknown

I don't want to mention any specific version here. Now my questions are:

why sometimes maven can resolve dependencies like the above "Spring" Module and sometimes can't?(SpringBootLocalstack module where I didn't mention version no)
How can we achieve compatibility safety for our maven dependencies? Is there any plugin (already tried dependency analyzer and version maven plugin but no luck)
How can we upgrade our old project to new maven dependencies without breaking the existing project feature?

Thanks in advance.

CodePudding user response：

You have declared 'org.springframework.boot' as the parent module of both modules. So if some jars and artifacts like 'com.amazonaws' do not exist in 'org.springframework.boot', they won't be resolved in your project. These dependencies are not announced in 'Spring' module in your project and whatever you have declared in it, can be found in 'org.springframework.boot', then resolved. If you do not declare a 'version' tag in your pom, I guess the version of the parent (here 2.6.1) will be considered for your module version.

CodePudding user response：

I think BOM (Bill of Materials) may come into rescue. If we use BOM, we don't need to specify version numbers each time we add dependencies under same parent POM. For example:

<!-- https://mvnrepository.com/artifact/com.amazonaws/aws-java-sdk-bom -->
<dependency>
    <groupId>com.amazonaws</groupId>
    <artifactId>aws-java-sdk-bom</artifactId>
    <version>1.12.138</version>
    <type>pom</type>
    <scope>import</scope>
</dependency>