POM使用<exclusions>標(biāo)簽排除多個(gè)依賴包的同一個(gè)依賴時(shí)膳音，需要注意pom依賴的順序問題（當(dāng)然也可以每個(gè)都進(jìn)行排除）。

1 正常場景

以下為SpringBoot相關(guān)的依賴：

<!-- Spring Dependencies -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
            <exclusions>
                <exclusion>
                    <groupId>org.springframework.boot</groupId>
                    <artifactId>spring-boot-starter-logging</artifactId>
                </exclusion>
                <exclusion>
                    <artifactId>spring-boot-starter-json</artifactId>
                    <groupId>org.springframework.boot</groupId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-log4j2</artifactId>
        </dependency>
        <dependency>
            <!-- Commons Logging to Log4j2 -->
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-jcl</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-thymeleaf</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-jdbc</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-aop</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-configuration-processor</artifactId>
            <optional>true</optional>
        </dependency>

運(yùn)行后控制臺(tái)結(jié)果如下：

1.png

2 異常場景

當(dāng)我調(diào)整了pom中Spring的依賴順序后如下（其余保持完全不變）：

<!-- Spring Dependencies -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-thymeleaf</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-jdbc</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-aop</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-configuration-processor</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
            <exclusions>
                <exclusion>
                    <groupId>org.springframework.boot</groupId>
                    <artifactId>spring-boot-starter-logging</artifactId>
                </exclusion>
                <exclusion>
                    <artifactId>spring-boot-starter-json</artifactId>
                    <groupId>org.springframework.boot</groupId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-log4j2</artifactId>
        </dependency>
        <dependency>
            <!-- Commons Logging to Log4j2 -->
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-jcl</artifactId>
        </dependency>

再次啟動(dòng)應(yīng)用時(shí)弟晚，控制臺(tái)打印如下：

2.png

3 疑問和思考

3.png

現(xiàn)象：經(jīng)過依賴分析行楞，確實(shí)日志沖突了（spring-boot-starter-jdbc、spring-boot-starter-thymeleaf）
疑問：難道pom的依賴還有順序的要求锋叨？

經(jīng)過反復(fù)驗(yàn)證菊匿，發(fā)現(xiàn)當(dāng)MAVEN使用<exclusions>標(biāo)簽時(shí)付呕，需要在依賴的第一個(gè)包進(jìn)行排除，如下：

<!-- Spring Dependencies -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-thymeleaf</artifactId>
            <exclusions>
                <exclusion>
                    <groupId>org.springframework.boot</groupId>
                    <artifactId>spring-boot-starter-logging</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-jdbc</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-aop</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-configuration-processor</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-log4j2</artifactId>
        </dependency>
        <dependency>
            <!-- Commons Logging to Log4j2 -->
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-jcl</artifactId>
        </dependency>