hadoop3.x：Sequence File序列化文件-读文件-马育民老师

# 创建maven工程

略

[idea创建maven工程必须修改idea配置](https://www.malaoshi.top/show_1IXSDwcJyst.html "idea创建maven工程必须修改idea配置")

# pom.xml

```
<dependencies>
	<dependency>
		<groupId>org.apache.hadoop</groupId>
		<artifactId>hadoop-common</artifactId>
		<version>3.0.3</version>
	</dependency>
	<dependency>
		<groupId>org.apache.hadoop</groupId>
		<artifactId>hadoop-hdfs</artifactId>
		<version>3.0.3</version>
	</dependency>
	<dependency>
		<groupId>org.apache.hadoop</groupId>
		<artifactId>hadoop-client</artifactId>
		<version>3.0.3</version>
	</dependency>
</dependencies>
```

在 pom.xml 点击右键 -> 【maven】 -> 【reimport】 导入依赖

# log4j.properties

打印 hadoop debug 信息

在 `resources` 文件夹下创建 `log4j.properties` 文件，内容如下：

```
log4j.rootLogger=DEBUG, stdout
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d %p [%c] - %m%n
```

# java

```
package top.malaoshi;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IOUtils;
import org.apache.hadoop.io.SequenceFile;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.util.ReflectionUtils;

public class Read {    
	
	public static void main(String[] args) throws Exception {
        //设置客户端运行身份 以root去操作访问HDFS
        System.setProperty("HADOOP_USER_NAME","root");
        //Configuration 用于指定相关参数属性
        Configuration conf = new Configuration();

//指定要读取的文件
        Path path=new Path("hdfs://hadoop1:8020/4.txt.gz");
        SequenceFile.Reader.Option option1 = SequenceFile.Reader.file(path);

SequenceFile.Reader reader = null;
        try {
            reader = new SequenceFile.Reader(conf,option1);
            //通过反射创建key
            Writable key = (Writable) ReflectionUtils.newInstance(
                    reader.getKeyClass(), conf);
            //通过反射创建value
            Writable value = (Writable) ReflectionUtils.newInstance(
                    reader.getValueClass(), conf);

while (reader.next(key, value)) {
                System.out.println(key+"===="+value);
            }
        } finally {
            IOUtils.closeStream(reader);
        }
    }
	
}

```

原文出处：/show_1IX2AIIojnL0.html