利用编程从HBASE中读取学生成绩,并实现计算每个学生成绩平均分和每门课程成绩平均分,用MapReduce方法,使用Java API编程。表中的内容是学号作为行键,姓名和学科作为列族,学科有语文数学英语物理,以及成绩
时间: 2023-12-10 09:06:11 浏览: 58
好的,这里是基于你给出的数据结构,利用Java API编程从HBase中读取学生成绩并实现计算每个学生成绩平均分和每门课程成绩平均分的步骤。
1. 定义HBase的配置信息和表名
```java
Configuration conf = HBaseConfiguration.create();
TableName tableName = TableName.valueOf("student_scores");
```
2. 创建HBase连接和表对象
```java
Connection connection = ConnectionFactory.createConnection(conf);
Table table = connection.getTable(tableName);
```
3. 定义MapReduce作业
```java
Job job = Job.getInstance(conf, "CalculateScores");
job.setJarByClass(CalculateScores.class);
job.setMapperClass(ScoreMapper.class);
job.setReducerClass(ScoreReducer.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(FloatWritable.class);
```
4. 实现Mapper类,读取HBase中的数据,并将每个学生的成绩和课程作为键值对传递给Reducer类
```java
public static class ScoreMapper extends TableMapper<Text, FloatWritable> {
private Text outKey = new Text();
private FloatWritable outValue = new FloatWritable();
public void map(ImmutableBytesWritable row, Result value, Context context) throws IOException, InterruptedException {
String studentId = new String(row.get());
String name = new String(value.getValue(Bytes.toBytes("name"), Bytes.toBytes("name")));
String course = new String(value.getColumnLatestCell(Bytes.toBytes("score"), Bytes.toBytes("course")).getValue());
float score = Float.parseFloat(new String(value.getColumnLatestCell(Bytes.toBytes("score"), Bytes.toBytes(course)).getValue()));
outKey.set(studentId + "," + name + "," + course);
outValue.set(score);
context.write(outKey, outValue);
}
}
```
5. 实现Reducer类,计算每个学生的平均分和每门课程的平均分
```java
public static class ScoreReducer extends Reducer<Text, FloatWritable, Text, FloatWritable> {
private FloatWritable outValue = new FloatWritable();
public void reduce(Text key, Iterable<FloatWritable> values, Context context) throws IOException, InterruptedException {
float sum = 0;
int count = 0;
for (FloatWritable value : values) {
sum += value.get();
count++;
}
float avg = sum / count;
outValue.set(avg);
context.write(key, outValue);
}
}
```
6. 运行MapReduce作业并输出结果
```java
if (job.waitForCompletion(true)) {
Scan scan = new Scan();
ResultScanner scanner = table.getScanner(scan);
float sum = 0;
int count = 0;
float chineseSum = 0;
int chineseCount = 0;
float mathSum = 0;
int mathCount = 0;
float englishSum = 0;
int englishCount = 0;
float physicsSum = 0;
int physicsCount = 0;
for (Result result : scanner) {
String studentId = new String(result.getRow());
String name = new String(result.getValue(Bytes.toBytes("name"), Bytes.toBytes("name")));
String course = new String(result.getColumnLatestCell(Bytes.toBytes("score"), Bytes.toBytes("course")).getValue());
float score = Float.parseFloat(new String(result.getColumnLatestCell(Bytes.toBytes("score"), Bytes.toBytes(course)).getValue()));
sum += score;
count++;
if (course.equals("语文")) {
chineseSum += score;
chineseCount++;
} else if (course.equals("数学")) {
mathSum += score;
mathCount++;
} else if (course.equals("英语")) {
englishSum += score;
englishCount++;
} else if (course.equals("物理")) {
physicsSum += score;
physicsCount++;
}
}
System.out.println("Average score: " + sum / count);
System.out.println("Chinese average score: " + chineseSum / chineseCount);
System.out.println("Math average score: " + mathSum / mathCount);
System.out.println("English average score: " + englishSum / englishCount);
System.out.println("Physics average score: " + physicsSum / physicsCount);
}
```
以上就是利用Java API编程从HBase中读取学生成绩并实现计算每个学生成绩平均分和每门课程成绩平均分的步骤。