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
时间: 2024-02-25 13:58:49 浏览: 37
以下是从HBase中读取学生成绩并计算平均分的Java代码示例:
```java
import java.io.IOException;
import java.util.*;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hbase.Cell;
import org.apache.hadoop.hbase.CellUtil;
import org.apache.hadoop.hbase.HBaseConfiguration;
import org.apache.hadoop.hbase.TableName;
import org.apache.hadoop.hbase.client.*;
import org.apache.hadoop.hbase.filter.*;
import org.apache.hadoop.hbase.util.Bytes;
import org.apache.hadoop.io.*;
import org.apache.hadoop.mapreduce.*;
import org.apache.hadoop.mapreduce.lib.input.*;
import org.apache.hadoop.mapreduce.lib.output.*;
public class HBaseAverageScore {
private static Configuration conf = null;
private static Connection conn = null;
private static Admin admin = null;
private static Table table = null;
// 初始化HBase配置
static {
conf = HBaseConfiguration.create();
conf.set("hbase.zookeeper.quorum", "localhost");
try {
conn = ConnectionFactory.createConnection(conf);
admin = conn.getAdmin();
table = conn.getTable(TableName.valueOf("scores"));
} catch (IOException e) {
e.printStackTrace();
}
}
// 关闭资源
private static void close() {
if (admin != null) {
try {
admin.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if (conn != null) {
try {
conn.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if (table != null) {
try {
table.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
// 从HBase中读取学生成绩
public static class HBaseMapper extends TableMapper<Text, IntWritable> {
private static final IntWritable one = new IntWritable(1);
private Text keyText = new Text();
private IntWritable valueInt = new IntWritable();
// 读取学生成绩
public void map(ImmutableBytesWritable row, Result value, Context context) throws IOException, InterruptedException {
for (Cell cell : value.rawCells()) {
String[] items = Bytes.toString(CellUtil.cloneQualifier(cell)).split("_");
String course = items[0];
String student = Bytes.toString(CellUtil.cloneRow(cell));
int score = Bytes.toInt(CellUtil.cloneValue(cell));
// 计算每个学生的平均分
keyText.set(student);
valueInt.set(score);
context.write(keyText, valueInt);
// 计算每门课程的平均分
keyText.set(course);
valueInt.set(score);
context.write(keyText, valueInt);
}
}
}
// 计算平均分
public static class HBaseReducer extends Reducer<Text, IntWritable, Text, DoubleWritable> {
private DoubleWritable result = new DoubleWritable();
public void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {
int sum = 0;
int count = 0;
for (IntWritable val : values) {
sum += val.get();
count++;
}
double average = (double) sum / count;
result.set(average);
context.write(key, result);
}
}
// 主函数
public static void main(String[] args) throws Exception {
// 配置MapReduce作业
Job job = Job.getInstance(conf, "HBaseAverageScore");
job.setJarByClass(HBaseAverageScore.class);
Scan scan = new Scan();
scan.setCaching(500);
scan.setCacheBlocks(false);
FilterList filters = new FilterList(FilterList.Operator.MUST_PASS_ALL);
filters.addFilter(new FamilyFilter(CompareFilter.CompareOp.EQUAL, new BinaryComparator(Bytes.toBytes("info"))));
scan.setFilter(filters);
TableMapReduceUtil.initTableMapperJob("scores", scan, HBaseMapper.class, Text.class, IntWritable.class, job);
job.setReducerClass(HBaseReducer.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(DoubleWritable.class);
FileOutputFormat.setOutputPath(job, new Path(args[0]));
System.exit(job.waitForCompletion(true) ? 0 : 1);
close();
}
}
```
在该代码中,我们使用了HBase的Java API来读取学生成绩数据,并使用MapReduce方法计算每个学生的平均分和每门课程的平均分。具体实现中,我们首先使用TableMapper来读取HBase表中的数据,并将其转换成MapReduce作业所需的键值对格式。然后,我们使用Reducer来计算每个学生和每门课程的平均分。最后,我们将计算结果输出到指定路径下的文件中。
需要注意的是,由于HBase是一种分布式数据库,因此我们需要配置HBase的相关参数,如zookeeper的地址等。另外,由于HBase的表结构是动态的,我们需要对表的列族和列名进行相应的过滤和处理,以便正确地读取数据。