解决：Server IPC version 9 cannot communicate with client version 4

使用idea的maven项目运行mapreduce程序Server IPC version 9 cannot communicate with client version 4

原因：

Java初始化hdfs client时出现的，原因是maven依赖的版本和hdfs的版本不一致

maven仓库中的hadoop-core最高只有1.2.1版本， 不能加这个配置， 使用hadoop-common + hadoop-hdfs + hadoop-client的2.7.1版本即可

我的pom文件：

<?xml version="1.0" encoding="UTF-8"?>
<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/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>hadoop01</groupId>
    <artifactId>hadoop01</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>
        <!--<dependency>-->
            <!--<groupId>org.apache.hadoop</groupId>-->
            <!--<artifactId>hadoop-core</artifactId>-->
            <!--<version>1.2.1</version>-->
        <!--</dependency>-->
        <dependency>
            <groupId>org.apache.hadoop</groupId>
            <artifactId>hadoop-common</artifactId>
            <version>2.7.1</version>
        </dependency>
        <dependency>
            <groupId>org.apache.hadoop</groupId>
            <artifactId>hadoop-hdfs</artifactId>
            <version>2.7.1</version>
        </dependency>

        <dependency>
            <groupId>org.apache.hadoop</groupId>
            <artifactId>hadoop-client</artifactId>
            <version>2.7.1</version>

        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <artifactId>maven-dependency-plugin</artifactId>
                <configuration>
                    <excludeTransitive>false</excludeTransitive>
                    <stripVersion>true</stripVersion>
                    <outputDirectory>./lib</outputDirectory>
                </configuration>

            </plugin>
        </plugins>
    </build>
</project>