maven Missing artifact 异常

错误信息如下:
12-7-29 上午11时44分06秒: Missing artifact mysql:mysqlconnectorjava:jar:5.1.19:compile

架构如下:  parent 项目负责下载jar包， 配置如下:
<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/maven-v4_0_0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.wjj.example</groupId>
  <artifactId>example-parent</artifactId>
  <packaging>pom</packaging>
  <version>0.0.1-SNAPSHOT</version>
  <name>example-parent</name>
  <url>http://maven.apache.org</url>
 
  <modules>
  <module>../example-core</module>
  </modules>
 
<properties>
  <project.build.sourceEncoding>UTF8</project.build.sourceEncoding>
  <spring.version>3.1.1.RELEASE</spring.version>
  </properties>

<dependencyManagement>
<dependencies>
<dependency>
  <groupId>${project.groupId}</groupId>
  <artifactId>example-parent</artifactId>
  <version>0.0.1SNAPSHOT</version>
  </dependency>
<dependency>
  <groupId>junit</groupId>
  <artifactId>junit</artifactId>
  <version>4.10</version>
  <scope>test</scope>
  </dependency>
<dependency>
  <groupId>org.springframework</groupId>
  <artifactId>springtest</artifactId>
  <version>${spring.version}</version>
  </dependency>
<dependency>
  <groupId>org.springframework</groupId>
  <artifactId>springorm</artifactId>
  <version>${spring.version}</version>
  </dependency>
<dependency>
  <groupId>org.springframework</groupId>
  <artifactId>springcore</artifactId>
  <version>${spring.version}</version>
  </dependency>
<dependency>
  <groupId>org.springframework</groupId>
  <artifactId>springaop</artifactId>
  <version>${spring.version}</version>
  </dependency>
<dependency>
  <groupId>org.springframework</groupId>
  <artifactId>springbeans</artifactId>
  <version>${spring.version}</version>
  </dependency>
<dependency>
  <groupId>org.springframework</groupId>
  <artifactId>springcontext</artifactId>
  <version>${spring.version}</version>
  </dependency>
<dependency>
  <groupId>org.springframework</groupId>
  <artifactId>springwebmvc</artifactId>
  <version>${spring.version}</version>
  </dependency>
<!--   hibernate start  -->
<dependency>
  <groupId>org.hibernate.javax.persistence</groupId>
  <artifactId>hibernatejpa2.0api</artifactId>
  <version>1.0.1.Final</version>
  </dependency>
<dependency>
  <groupId>org.hibernate</groupId>
  <artifactId>hibernatecore</artifactId>
  <version>3.6.10.Final</version>
  </dependency>
<dependency>
  <groupId>org.slf4j</groupId>
  <artifactId>slf4japi</artifactId>
  <version>1.6.4</version>
  </dependency>
<dependency>
  <groupId>javassist</groupId>
  <artifactId>javassist</artifactId>
  <version>3.12.1.GA</version>
  </dependency>
<!--    hibernate end -->
<!--  database start -->
<dependency>
  <groupId>mysql</groupId>
  <artifactId>mysqlconnectorjava</artifactId>
  <version>5.1.19</version>
  </dependency>
<dependency>
  <groupId>commonsdbcp</groupId>
  <artifactId>commonsdbcp</artifactId>
  <version>1.4</version>
  </dependency>
<!--  database end -->
<!-- j2se -->
<dependency>
  <groupId>com.kenai.nbpwr</groupId>
  <artifactId>javaxinject</artifactId>
  <version>1.0201002241208</version>
  </dependency>
<dependency>
  <groupId>org.hibernate</groupId>
  <artifactId>hibernatevalidator</artifactId>
  <version>4.2.0.Final</version>
<exclusions>
<exclusion>
  <groupId>org.hibernate</groupId>
  <artifactId>hibernatecommonsannotations</artifactId>
  </exclusion>
  </exclusions>
  </dependency>
<dependency>
  <groupId>javax.validation</groupId>
  <artifactId>validationapi</artifactId>
  <version>1.0.0.GA</version>
  </dependency>
<!--   j2se end -->
<dependency>
  <groupId>org.aspectj</groupId>
  <artifactId>aspectjweaver</artifactId>
  <version>1.6.11</version>
  </dependency>
<!--   servlet+jstl+jsp -->
<dependency>
  <groupId>servletapi</groupId>
  <artifactId>servletapi</artifactId>
  <version>2.4</version>
  <scope>provided</scope>
  </dependency>
<dependency>
  <groupId>javax.servlet.jsp</groupId>
  <artifactId>jspapi</artifactId>
  <version>2.2</version>
  <scope>provided</scope>
  </dependency>
<dependency>
  <groupId>jstl</groupId>
  <artifactId>jstl</artifactId>
  <version>1.2</version>
  </dependency>
<dependency>
  <groupId>taglibs</groupId>
  <artifactId>standard</artifactId>
  <version>1.1.1</version>
  </dependency>
<dependency>
  <groupId>commonsio</groupId>
  <artifactId>commonsio</artifactId>
  <version>2.3</version>
  </dependency>
<dependency>
  <groupId>commonslogging</groupId>
  <artifactId>commonslogging</artifactId>
  <version>1.1.1</version>
  </dependency>
<dependency>
  <groupId>commonsfileupload</groupId>
  <artifactId>commonsfileupload</artifactId>
  <version>1.2.2</version>
  </dependency>
<dependency>
  <groupId>jsptags</groupId>
  <artifactId>pagertaglib</artifactId>
  <version>2.0</version>
  </dependency>
<!-- json -->
<dependency>
  <groupId>org.codehaus.jackson</groupId>
  <artifactId>jacksoncoreasl</artifactId>
  <version>1.9.6</version>
  </dependency>
<dependency>
  <groupId>org.codehaus.jackson</groupId>
  <artifactId>jacksonmapperasl</artifactId>
  <version>1.9.6</version>
  </dependency>
  </dependencies>
  </dependencyManagement>
 
<build>
<pluginManagement>
<plugins>
<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>mavencompilerplugin</artifactId>
  <version>2.3.2</version>
<configuration>
  <source>1.6</source>
  <target>1.6</target>
  </configuration>
  </plugin>
<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>mavenresourcesplugin</artifactId>
<configuration>
  <encoding>UTF8</encoding>
  </configuration>
  </plugin>
<plugin>
  <groupId>org.mortbay.jetty</groupId>
<!--   使用的是jettymavenplugin的插件 -->
  <artifactId>jettymavenplugin</artifactId>
<configuration>
  <scanIntervalSeconds>2000</scanIntervalSeconds>
<webApp>
<!--   上下文路径 -->
  <contextPath>/stu</contextPath>
  </webApp>
<connectors>
<connector implementation="org.eclipse.jetty.server.nio.SelectChannelConnector">
<!--   端口号 -->
  <port>8787</port>
  <maxIdleTime>500000</maxIdleTime>
  </connector>
  </connectors>
  </configuration>
  </plugin>
  </plugins>
  </pluginManagement>
  </build>
</project>



子模块配置如下:
<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/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>com.wjj.example</groupId>
<artifactId>example-parent</artifactId>
<version>0.0.1-SNAPSHOT</version>
<relativePath>../example-parent/pom.xml</relativePath>
</parent>



<artifactId>example-core</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>example-core</name>
<url>http://maven.apache.org</url>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysqlconnectorjava</artifactId>
</dependency>
</dependencies>
</project>

就会报上面那个错误。 请教大家一下，解决方案谢谢。!!。