背景

通过maven的GAV完全可以避免同一个构件在项目中使用===》也就是打包出来最终同一个GA的构件一定只有一个

但是除了这种GA构件唯一我们在java项目中还经常碰到class完全相同的场景比如典型的就是mail

参考邮件无法发送之maven项目引入新依赖问题

像这种构件名称不一样导致出现class重复的问题也不再少数

对于这种问题怎么解决呢？？？

对策

其实说难不难说易不易~我们需要做的是将对应的class进行check下是否存在重复即可！

抽象说来就是说一堆文件夹中我们要找到文件路径完全相同的文件

方案1

将所有的jar遍历里面的class文件进行输出后排序发现有重复就输出~

比如我们可以一些第三方脚本show-duplicate-java-classes

在对应目录执行后输出如下

11 (1@3): ./woden-impl-dom-1.0M8.jar ./stax-api-1.0.1.jar ./xml-apis-1.3.04.jar
    1   javax/xml/namespace/QName.class
12 (223@2): ./quartz-all-1.6.1.jar ./quartz-1.6.1.jar
    1   org/quartz/impl/jdbcjobstore/JobStoreSupport$VoidTransactionCallback.class
    2   org/quartz/impl/jdbcjobstore/JobStoreSupport$25.class
    3   org/quartz/impl/StdJobRunShellFactory.class
    4   org/quartz/impl/QuartzServer.class

这样的话完全可以根据对应的问题进行修正

方案2

使用maven插件在编译期就发现问题【当然会忽略一些容器提供的jar】但是绝大部分是OK的比如如下

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-enforcer-plugin</artifactId>
    <version>1.4.1</version>
    <executions>
        <execution>
            <id>enforce-ban-duplicate-classes</id>
            <goals>
                <goal>enforce</goal>
            </goals>
            <configuration>
                <rules>
                    <banDuplicateClasses>
                        <ignoreClasses>
                            <ignoreClass>javax.*</ignoreClass>
                            <ignoreClass>org.junit.*</ignoreClass>
                            <ingoreClass>org.aspectj.*</ingoreClass>
                            <ingoreClass>org.jboss.netty.*</ingoreClass>
                            <ingoreClass>org.apache.juli.*</ingoreClass>
                            <ingoreClass>org.apache.commons.logging.*</ingoreClass>
                            <ingoreClass>org.apache.log4j.*</ingoreClass>
                            <ingoreClass>org.objectweb.asm.*</ingoreClass>
                            <ingoreClass>org.parboiled.*</ingoreClass>
                            <ingoreClass>org.apache.xmlbeans.xml.stream.*</ingoreClass>
                            <ingoreClass>org.json.JSONString</ingoreClass>
                        </ignoreClasses>
                        <findAllDuplicates>true</findAllDuplicates>
                    </banDuplicateClasses>
                </rules>
                <fail>true</fail>
            </configuration>
        </execution>
    </executions>
    <dependencies>
        <dependency>
            <groupId>org.codehaus.mojo</groupId>
            <artifactId>extra-enforcer-rules</artifactId>
            <version>1.0-beta-6</version>
        </dependency>
    </dependencies>
</plugin>

比如某位同学引入了新的依赖导致系统中出现了一些新的class和原先重复了那么在maven编译的过程中就会报错

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-enforcer-plugin:1.4.1:enforce (enforce-ban-duplicate-classes) on project web: Some Enforcer rules have failed. Look above for specific messages explaining why the rule failed. -> [Help 1]
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException
[ERROR]
[ERROR] After correcting the problems, you can resume the build with the command
[ERROR]   mvn <goals> -rf :web

可以查看到详细的报错信息

[INFO] --- maven-enforcer-plugin:1.4.1:enforce (enforce-ban-duplicate-classes) @ web ---
[INFO] Adding ignore: javax.*
[INFO] Adding ignore: org.junit.*
[INFO] Adding ignore: org.aspectj.*
[INFO] Adding ignore: org.jboss.netty.*
[INFO] Adding ignore: org.apache.juli.*
[INFO] Adding ignore: org.apache.commons.logging.*
[INFO] Adding ignore: org.apache.log4j.*
[INFO] Adding ignore: org.objectweb.asm.*
[INFO] Adding ignore: org.parboiled.*
[INFO] Adding ignore: org.apache.xmlbeans.xml.stream.*
[WARNING] Rule 0: org.apache.maven.plugins.enforcer.BanDuplicateClasses failed with message:
Duplicate classes found:
  Found in:
    org.skyscreamer:jsonassert:jar:1.4.0:compile
    org.json:json:jar:20140107:compile
  Duplicate classes:
    org/json/JSONString.class

我们可以知道org.json.JSONString这个类在两个jar中都出现了~需要注意！

maven神器插件enforce查找重复类

背景

对策

方案1

方案2

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