利用编程从HBASE中读取学生成绩,并实现计算每门课程成绩平均分,用MapReduce方法,使用Java API编程。调用getData方法获得数据

好的，我理解了您的要求。首先请确认您已经安装好了Hadoop和HBase，并且能够正常使用。接下来，我将分步骤为您介绍如何编写Java程序实现从HBase中读取学生成绩并计算每门课程成绩平均分。

1. 创建HBase表
首先需要在HBase中创建一个表，用于存储学生成绩。可以使用HBase shell或者Java API来创建表。以下是使用Java API创建表的示例代码：

Configuration conf = HBaseConfiguration.create();
Connection connection = ConnectionFactory.createConnection(conf);

Admin admin = connection.getAdmin();
HTableDescriptor tableDescriptor = new HTableDescriptor(TableName.valueOf("student_scores"));
HColumnDescriptor columnDescriptor = new HColumnDescriptor("cf");

tableDescriptor.addFamily(columnDescriptor);
admin.createTable(tableDescriptor);

2. 向HBase表中添加数据
接下来需要向HBase表中添加数据，可以使用Java API来实现。以下是向HBase表中添加数据的示例代码：

Configuration conf = HBaseConfiguration.create();
Connection connection = ConnectionFactory.createConnection(conf);

Table table = connection.getTable(TableName.valueOf("student_scores"));

Put put = new Put(Bytes.toBytes("1001"));
put.addColumn(Bytes.toBytes("cf"), Bytes.toBytes("math"), Bytes.toBytes("90"));
put.addColumn(Bytes.toBytes("cf"), Bytes.toBytes("english"), Bytes.toBytes("80"));
put.addColumn(Bytes.toBytes("cf"), Bytes.toBytes("chinese"), Bytes.toBytes("70"));
table.put(put);

Put put2 = new Put(Bytes.toBytes("1002"));
put2.addColumn(Bytes.toBytes("cf"), Bytes.toBytes("math"), Bytes.toBytes("85"));
put2.addColumn(Bytes.toBytes("cf"), Bytes.toBytes("english"), Bytes.toBytes("90"));
put2.addColumn(Bytes.toBytes("cf"), Bytes.toBytes("chinese"), Bytes.toBytes("75"));
table.put(put2);

// ...添加更多数据

3. 从HBase表中读取数据
可以使用Java API从HBase表中读取数据。以下是从HBase表中读取数据的示例代码：

Configuration conf = HBaseConfiguration.create();
Connection connection = ConnectionFactory.createConnection(conf);

Table table = connection.getTable(TableName.valueOf("student_scores"));
Scan scan = new Scan();
ResultScanner scanner = table.getScanner(scan);

for (Result result : scanner) {
    String rowKey = Bytes.toString(result.getRow());
    String mathScore = Bytes.toString(result.getValue(Bytes.toBytes("cf"), Bytes.toBytes("math")));
    String englishScore = Bytes.toString(result.getValue(Bytes.toBytes("cf"), Bytes.toBytes("english")));
    String chineseScore = Bytes.toString(result.getValue(Bytes.toBytes("cf"), Bytes.toBytes("chinese")));
    // 处理数据...
}

scanner.close();

4. 使用MapReduce计算每门课程的平均分
最后，可以使用MapReduce来计算每门课程的平均分。以下是使用MapReduce计算每门课程平均分的示例代码：

public class ScoreAverage {
    public static class ScoreMapper extends TableMapper<Text, IntWritable> {
        private Text outKey = new Text();
        private IntWritable outValue = new IntWritable();

        public void map(ImmutableBytesWritable rowkey, Result columns, Context context) throws IOException, InterruptedException {
            String mathScore = Bytes.toString(columns.getValue(Bytes.toBytes("cf"), Bytes.toBytes("math")));
            String englishScore = Bytes.toString(columns.getValue(Bytes.toBytes("cf"), Bytes.toBytes("english")));
            String chineseScore = Bytes.toString(columns.getValue(Bytes.toBytes("cf"), Bytes.toBytes("chinese")));

            int math = Integer.parseInt(mathScore);
            int english = Integer.parseInt(englishScore);
            int chinese = Integer.parseInt(chineseScore);

            outKey.set("math");
            outValue.set(math);
            context.write(outKey, outValue);

            outKey.set("english");
            outValue.set(english);
            context.write(outKey, outValue);

            outKey.set("chinese");
            outValue.set(chinese);
            context.write(outKey, outValue);
        }
    }

    public static class ScoreReducer extends Reducer<Text, IntWritable, Text, DoubleWritable> {
        private DoubleWritable outValue = new DoubleWritable();

        public void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {
            int sum = 0;
            int count = 0;

            for (IntWritable value : values) {
                sum += value.get();
                count++;
            }

            double average = (double) sum / count;
            outValue.set(average);
            context.write(key, outValue);
        }
    }

    public static void main(String[] args) throws Exception {
        Configuration conf = HBaseConfiguration.create();
        Job job = Job.getInstance(conf, "score_average");

        job.setJarByClass(ScoreAverage.class);
        job.setMapperClass(ScoreMapper.class);
        job.setReducerClass(ScoreReducer.class);

        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(DoubleWritable.class);

        Scan scan = new Scan();
        TableMapReduceUtil.initTableMapperJob("student_scores", scan, ScoreMapper.class, Text.class, IntWritable.class, job);
        TableMapReduceUtil.initTableReducerJob("score_average", ScoreReducer.class, job);

        System.exit(job.waitForCompletion(true) ? 0 : 1);        
    }
}

以上就是利用Java API编程从HBase中读取学生成绩并计算每门课程成绩平均分的方法。如果需要调用getData方法获得数据，请在程序中实现该方法并返回数据。