MapReduce实现矩阵相乘java代码

以下是使用MapReduce实现矩阵相乘的Java代码：

Mapper类：

public class MatrixMapper extends Mapper<LongWritable, Text, Text, Text> {
    private Text keyOut = new Text();
    private Text valueOut = new Text();
    private int k;

    @Override
    protected void setup(Context context) throws IOException, InterruptedException {
        super.setup(context);
        Configuration configuration = context.getConfiguration();
        k = configuration.getInt("k", 0);
    }

    @Override
    protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
        String[] values = value.toString().split(",");
        if (values.length != 3) {
            throw new IOException("Invalid input format");
        }
        int i = Integer.parseInt(values[0]);
        int j = Integer.parseInt(values[1]);
        int v = Integer.parseInt(values[2]);
        if (i < 0 || i >= k || j < 0 || j >= k) {
            throw new IOException("Invalid input format");
        }
        keyOut.set(String.valueOf(j));
        valueOut.set("A," + i + "," + v);
        context.write(keyOut, valueOut);
        keyOut.set(String.valueOf(i));
        valueOut.set("B," + j + "," + v);
        context.write(keyOut, valueOut);
    }
}

Reducer类：

public class MatrixReducer extends Reducer<Text, Text, Text, IntWritable> {
    private IntWritable valueOut = new IntWritable();
    private Map<Integer, Integer> aMap = new HashMap<>();
    private Map<Integer, Integer> bMap = new HashMap<>();

    @Override
    protected void reduce(Text key, Iterable<Text> values, Context context) throws IOException, InterruptedException {
        for (Text value : values) {
            String[] fields = value.toString().split(",");
            if (fields.length != 3) {
                throw new IOException("Invalid input format");
            }
            String matrixName = fields[0];
            int i = Integer.parseInt(fields[1]);
            int v = Integer.parseInt(fields[2]);
            if ("A".equals(matrixName)) {
                aMap.put(i, v);
            } else if ("B".equals(matrixName)) {
                bMap.put(i, v);
            } else {
                throw new IOException("Invalid input format");
            }
        }
        int sum = 0;
        for (Map.Entry<Integer, Integer> entry : aMap.entrySet()) {
            int i = entry.getKey();
            int a = entry.getValue();
            Integer b = bMap.get(i);
            if (b != null) {
                sum += a * b;
            }
        }
        valueOut.set(sum);
        context.write(key, valueOut);
        aMap.clear();
        bMap.clear();
    }
}

Driver类：

public class MatrixMultiplication {
    public static void main(String[] args) throws Exception {
        if (args.length != 3) {
            System.err.println("Usage: MatrixMultiplication <inputPath> <outputPath> <k>");
            System.exit(1);
        }
        Configuration configuration = new Configuration();
        configuration.setInt("k", Integer.parseInt(args[2]));
        Job job = Job.getInstance(configuration, "Matrix Multiplication");
        job.setJarByClass(MatrixMultiplication.class);
        job.setMapperClass(MatrixMapper.class);
        job.setReducerClass(MatrixReducer.class);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(Text.class);
        FileInputFormat.addInputPath(job, new Path(args[0]));
        FileOutputFormat.setOutputPath(job, new Path(args[1]));
        System.exit(job.waitForCompletion(true) ? 0 : 1);
    }
}

这里假设输入文件的格式为每行三个用逗号分隔的数字，分别表示矩阵A或矩阵B的行、列和值。例如，输入文件中的一行可能是`0,0,1`，表示A矩阵的第0行第0列的值为1。