job.setmapperclass报错

如果您在使用 Hadoop MapReduce 进行开发时，调用 `job.setMapperClass` 时出现错误，请检查以下几点：

1. 是否正确导入了 `org.apache.hadoop.mapreduce.Job` 类和 `org.apache.hadoop.mapreduce.Mapper` 类。

2. 是否正确继承了 Mapper 类，且实现了 `map` 函数。例如：

public static class MyMapper extends Mapper<LongWritable, Text, Text, IntWritable>{
    @Override
    public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
        // TODO: 实现 map 函数
    }
}

3. 是否正确设置了 Mapper 类，例如：

Job job = new Job(conf, "myjob");
job.setMapperClass(MyMapper.class);
job.setMapOutputKeyClass(Text.class);
job.setMapOutputValueClass(IntWritable.class);

如果您已经检查了以上几点，仍然无法解决问题，请提供更多详细信息，我会尽力帮助您解决问题。

相关问题

Configuration conf = new Configuration(); Job job = Job.getInstance(conf, "word count"); job.setJarByClass(WordCountDriver.class); job.setMapperClass(WordCountMapper.class); job.setCombinerClass(WordCountReducer.class); job.setReducerClass(WordCountReducer.class); job.setOutputKeyClass(Text.class); job.setOutputValueClass(IntWritable.class); FileInputFormat.addInputPath(job, new Path(args[0])); FileOutputFormat.setOutputPath(job, new Path(args[1])); System.exit(job.waitForCompletion(true) ? 0 : 1);

这是一个使用Hadoop MapReduce框架实现的Word Count程序的驱动程序代码。其中`job.setMapperClass(WordCountMapper.class)`指定了Map阶段使用的Mapper类，`job.setReducerClass(WordCountReducer.class)`指定了Reduce阶段使用的Reducer类，`FileInputFormat.addInputPath(job, new Path(args[0]))`指定输入路径，`FileOutputFormat.setOutputPath(job, new Path(args[1]))`指定输出路径。程序最后调用`job.waitForCompletion(true)`提交作业并等待作业完成，`System.exit(job.waitForCompletion(true) ? 0 : 1)`表示当作业完成时退出程序并返回0，否则返回1。

public class MarketShareDriver { public static void main(String[] args) throws Exception { Configuration conf = new Configuration(); Job job = Job.getInstance(conf); job.setJarByClass(MarketShareDriver.class); job.setMapperClass(MarketShareMapper.class); job.setReducerClass(MarketShareReducer.class); job.setMapOutputKeyClass(Text.class); job.setMapOutputValueClass(Text.class); job.setOutputKeyClass(Text.class); job.setOutputValueClass(Text.class); Path inPath = new Path("data/phone.txt"); FileInputFormat.setInputPaths(job,inPath); Path outPath = new Path("data/PhoneMarketShare"); FileSystem fs = outPath.getFileSystem(conf); if (fs.exists(outPath)){ fs.delete(outPath,true); } FileOutputFormat.setOutputPath(job,outPath); boolean b = job.waitForCompletion(true); System.exit(b ? 0 : 1); } } 这段代码怎么修改才能把数据也存到MySQL中

要将数据存储到MySQL中，需要在Mapper或Reducer中添加连接MySQL的代码，并将结果写入MySQL中。以下是一个简单的示例：

1. 添加MySQL连接信息

// 定义MySQL连接信息
String driver = "com.mysql.jdbc.Driver";
String url = "jdbc:mysql://localhost:3306/test";
String username = "root";
String password = "password";

// 注册JDBC驱动程序
Class.forName(driver);

// 获取数据库连接
Connection conn = DriverManager.getConnection(url, username, password);

// 创建Statement对象
Statement stmt = conn.createStatement();

2. 在Mapper或Reducer中将结果写入MySQL中

// 将结果写入MySQL中
while (values.hasNext()) {
    // 获取一条记录
    Text value = values.next();
    String[] fields = value.toString().split(",");

    // 插入数据
    String sql = "INSERT INTO PhoneMarketShare (brand, marketShare) VALUES ('" + fields[0] + "', '" + fields[1] + "')";
    stmt.executeUpdate(sql);
}

完整代码如下所示：

public class MarketShareDriver {
    public static void main(String[] args) throws Exception {
        Configuration conf = new Configuration();
        Job job = Job.getInstance(conf);
        job.setJarByClass(MarketShareDriver.class);
        job.setMapperClass(MarketShareMapper.class);
        job.setReducerClass(MarketShareReducer.class);
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(Text.class);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(Text.class);
        Path inPath = new Path("data/phone.txt");
        FileInputFormat.setInputPaths(job,inPath);
        Path outPath = new Path("data/PhoneMarketShare");
        FileSystem fs = outPath.getFileSystem(conf);
        if (fs.exists(outPath)){
            fs.delete(outPath,true);
        }
        FileOutputFormat.setOutputPath(job,outPath);
        boolean b = job.waitForCompletion(true);

        // 将结果写入MySQL中
        if (b) {
            // 定义MySQL连接信息
            String driver = "com.mysql.jdbc.Driver";
            String url = "jdbc:mysql://localhost:3306/test";
            String username = "root";
            String password = "password";

            // 注册JDBC驱动程序
            Class.forName(driver);

            // 获取数据库连接
            Connection conn = DriverManager.getConnection(url, username, password);

            // 创建Statement对象
            Statement stmt = conn.createStatement();

            // 将结果写入MySQL中
            Iterator<OutputFormat> it = job.getOutputFormatClass().newInstance().getRecordWriter(null, job, null, null).asInstanceOf[FileOutputFormat<Text, Text>].getRecordWriter(job).asInstanceOf[SequenceFileRecordWriter[Text, Text]].getValues().iterator()
            while (it.hasNext()) {
                // 获取一条记录
                Text value = it.next();
                String[] fields = value.toString().split(",");

                // 插入数据
                String sql = "INSERT INTO PhoneMarketShare (brand, marketShare) VALUES ('" + fields[0] + "', '" + fields[1] + "')";
                stmt.executeUpdate(sql);
            }
        }

        System.exit(b ? 0 : 1);
    }
}

注意：以上代码仅作为示例，实际使用时需要根据实际情况进行修改和调整。