编写Java代码，用hive自定义函数实现，读取MySQL数据并写入hive表

好的，以下是Java代码示例（假设已经导入了相关的MySQL和Hive依赖）：

import java.sql.*;

import org.apache.hadoop.hive.ql.exec.UDFArgumentException;
import org.apache.hadoop.hive.ql.exec.UDFArgumentLengthException;
import org.apache.hadoop.hive.ql.exec.UDFArgumentTypeException;
import org.apache.hadoop.hive.ql.exec.UDFReturnType;
import org.apache.hadoop.hive.ql.metadata.HiveException;
import org.apache.hadoop.hive.ql.udf.generic.GenericUDF;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspectorFactory;
import org.apache.hadoop.hive.serde2.objectinspector.primitive.PrimitiveObjectInspectorFactory;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;

public class MySQLToHive extends GenericUDF {

    private Connection conn;

    @Override
    public ObjectInspector initialize(ObjectInspector[] arguments) throws UDFArgumentException {
        if (arguments.length != 3) {
            throw new UDFArgumentLengthException("The function MySQLToHive requires three arguments: jdbcUrl, username, and password");
        }

        for (ObjectInspector argument : arguments) {
            if (!argument.getTypeName().equals("string")) {
                throw new UDFArgumentTypeException(0, "The arguments to MySQLToHive must all be strings");
            }
        }

        return ObjectInspectorFactory.getStandardListObjectInspector(
                PrimitiveObjectInspectorFactory.writableStringObjectInspector);
    }

    @Override
    public Object evaluate(DeferredObject[] arguments) throws HiveException {
        String jdbcUrl = arguments[0].get().toString();
        String username = arguments[1].get().toString();
        String password = arguments[2].get().toString();

        try {
            if (conn == null || conn.isClosed()) {
                Class.forName("com.mysql.jdbc.Driver");
                conn = DriverManager.getConnection(jdbcUrl, username, password);
            }

            Statement stmt = conn.createStatement();
            ResultSet rs = stmt.executeQuery("SELECT * FROM my_table");

            List<Text> values = new ArrayList<Text>();
            while (rs.next()) {
                Text value = new Text(rs.getString("col1") + "\t" + rs.getString("col2") + "\t" + rs.getString("col3"));
                values.add(value);
            }

            return values;
        } catch (Exception e) {
            throw new HiveException(e);
        }
    }

    @Override
    public String getDisplayString(String[] children) {
        return "MySQLToHive(jdbcUrl, username, password)";
    }

    @Override
    public ObjectInspector getObjectInspector() throws UDFArgumentException {
        return ObjectInspectorFactory.getStandardListObjectInspector(
                PrimitiveObjectInspectorFactory.writableStringObjectInspector);
    }

    @Override
    public UDFReturnType getReturnType() {
        return UDFReturnType.LIST;
    }
}

这是一个自定义Hive函数，它将从MySQL中读取数据并将其写入Hive表。它需要三个参数：MySQL数据库的JDBC URL，用户名和密码。它将返回一个包含所有MySQL行数据的列表。修改SQL查询语句以适应你的表格结构。

在编译和打包Java代码后，将JAR文件上传到Hive服务器上，并在Hive中注册该函数：

ADD JAR /path/to/my_jar.jar;
CREATE TEMPORARY FUNCTION mysql_to_hive AS 'MySQLToHive';

现在你可以在Hive中使用该函数：

INSERT INTO my_hive_table SELECT * FROM TABLE(mysql_to_hive('jdbc:mysql://localhost:3306/my_database', 'my_username', 'my_password'));

这将从MySQL中读取所有行并将它们插入到名为 my_hive_table 的Hive表中。