webmagic之爬取数据存入HDFS

• 连接HDFS

添加以下的依赖

<dependency>
    <groupId>org.apache.hadoop</groupId>
    <artifactId>hadoop-common</artifactId>
    <version>2.7.3</version>
</dependency>
<dependency>
    <groupId>org.apache.hadoop</groupId>
    <artifactId>hadoop-client</artifactId>
    <version>2.7.3</version>
</dependency>
<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.5</version>
</dependency>
<dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>4.11</version>
    <scope>test</scope>
</dependency>

连接代码

Configuration config = new Configuration();
//(new URI("hdfs://192.168.146.110:9000"),config,"root")
FileSystem fs = FileSystem.get(URI.create("hdfs://192.168.146.110:9000"),config,"root");

注意import的包一定要对！！！

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataOutputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;

 

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开发时遇到下错误以下错误：

maven:java.lang.NoClassDefFoundError: org/apache/commons/io/Charsets

原因是：common-io 2.2下面是没有这个Charsets的，commons-io-2.5 下面就有了这个类，所以要升级commons版本

<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.5</version>
</dependency>

 

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• 将爬去到的数据以TXT写入hdfs文件中

封装连接方法

public static FileSystem connect() throws IOException, InterruptedException {
    Configuration config = new Configuration();
    //(new URI("hdfs://192.168.146.110:9000"),config,"root")
    FileSystem fs = FileSystem.get(URI.create("hdfs://192.168.146.110:9000"),config,"root");
    return fs;
}

封装追加的方法

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1.权限问题

原因：客户端追加写入会报错

java.io.IOException: Failed to replace a bad datanode on the existing pipeline due to no
 more good datanodes being available to try. (Nodes: current=[DatanodeInfoWithStorage[192.168.146.110:50010,DS-34d5abfb-b9c0-4aa7-aaa3-753010d9b3b6,DISK]], original=[DatanodeInfoWithStorage[192.168.146.110:50010,DS-34d5abfb-b9c0-4aa7-aaa3-753010d9b3b6,DISK]]). The current failed datanode replacement policy is DEFAULT, and a client may configure this via 'dfs.client.block.write.replace-datanode-on-failure.policy' in its configuration.

解决办法：

• 在hdfs.xml中添加配置

config.set("dfs.support.append", "true");
config.set("dfs.client.block.write.replace-datanode-on-failure.policy", "NEVER");
config.set("dfs.client.block.write.replace-datanode-on-failure.enable", "true");

• 封装方法，配置需要定义

config.set("dfs.support.append", "true");
config.set("dfs.client.block.write.replace-datanode-on-failure.policy", "NEVER");
config.set("dfs.client.block.write.replace-datanode-on-failure.enable", "true");

2.文件系统不支持问题

原因：ChecksumFileSystem不支持追加，DistributedFileSystem 才是hdfs采用的文件系统，这两个是不一样的文件系统 ，所以实现方式是不同的。也就是说DistributedFileSystem支持append，而它不支持。

解决办法：对filesystem进行类型转化。转化成DistributedFileSystem

又遇到强转报错原因是：程序使用的FileSystem是LocalFileSystem，是这个类org.apache.hadoop.fs.LocalFileSystem，并非org.apache.hadoop.hdfs.DistributedFileSystem这个类，所以强转会报错，你需要在conf中设置fs.default.name这个参数值，默认是file:///，所以FileSystem fs = FileSystem.get(conf);得到的是LocalFileSystem。

解决办法：conf.set("fs.default.name"，”hdfs://master:9000“)；

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完整代码如下：

public static void write(String str)  {
        Configuration config = new Configuration();
        config.set("fs.default.name", "hdfs://192.168.146.110:9000");
        config.set("dfs.support.append", "true");
        config.set("dfs.client.block.write.replace-datanode-on-failure.policy", "NEVER");
        config.set("dfs.client.block.write.replace-datanode-on-failure.enable", "true");

        try {
            DistributedFileSystem fs = (DistributedFileSystem) DistributedFileSystem.get(config);
            //文件必须存在
            FSDataOutputStream outpustream = fs.append(new Path("/hadoop/Zbgg.txt"));

            //System.getProperty("line.separator")换行
            outpustream.writeBytes(System.getProperty("line.separator"));
            outpustream.writeBytes(str);
            outpustream.close();
            fs.close();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }