resolution will not be reattempted until the update interval of nexus has elapsed or updates are forced

Maven在执行中报错：

- Failure to transfer org.slf4j:slf4j-api:jar:1.7.24 from http://localhost:8081/nexus/content/groups/public/ was cached in the local repository, 
    resolution will not be reattempted until the update interval of nexus has elapsed or updates are forced. 

原因是有些jar包没有完全下载下来，在编译中找不到jar包。

解决方法是 在setting.xml中增加一个更新策略，如下：

  <profiles>
    <profile>
　　<id>nexus</id>
    <!--所有请求均通过镜像 -->
    <repositories>
         <repository>
            <id>central</id>
            <url>http://central</url>
            <releases><enabled>true</enabled><updatePolicy>always</updatePolicy></releases>
            <snapshots><enabled>true</enabled><updatePolicy>always</updatePolicy></snapshots>
         </repository>
    </repositories>
    <pluginRepositories>
          <pluginRepository>
             <id>central</id>
             <url>http://central</url>
             <releases><enabled>true</enabled><updatePolicy>always</updatePolicy></releases>
             <snapshots><enabled>true</enabled><updatePolicy>always</updatePolicy></snapshots>
          </pluginRepository>
     </pluginRepositories>
    </profile>
    
    <profile>   
        <id>jdk-1.7</id>   
        <activation>   
          <activeByDefault>true</activeByDefault>   
          <jdk>1.7</jdk>   
        </activation>   
        <properties>   
            <maven.compiler.source>1.7</maven.compiler.source>   
            <maven.compiler.target>1.7</maven.compiler.target>   
            <maven.compiler.compilerVersion>1.7</maven.compiler.compilerVersion>   
        </properties>   
    </profile>
  </profiles>