详解 maven的pom.xml用<exclusion>解决版本问题

<!-- Struts2 --> 
    <dependency> 
      <groupId>org.apache.struts</groupId> 
      <artifactId>struts2-core</artifactId> 
      <version>${struts.version}</version> 
      <exclusions> 
        <exclusion> 
          <groupId>javassist</groupId> 
          <artifactId>javassist</artifactId> 
        </exclusion> 
        <exclusion> <!-- we prefer our explicit version, though it should be the same --> 
          <groupId>asm</groupId> 
          <artifactId>asm</artifactId> 
        </exclusion> 
        <exclusion> <!-- we prefer our explicit version, though it should be the same --> 
          <groupId>asm</groupId> 
          <artifactId>asm-commons</artifactId> 
        </exclusion> 
        <exclusion> <!-- we prefer our explicit version, though it should be the same --> 
          <groupId>org.ow2.asm</groupId> 
          <artifactId>asm</artifactId> 
        </exclusion> 
        <exclusion> <!-- we prefer our explicit version, though it should be the same --> 
          <groupId>org.ow2.asm</groupId> 
          <artifactId>asm-commons</artifactId> 
        </exclusion> 
      </exclusions> 
    </dependency>