java实现以下功能：扫描指定路径下的excel文件，若无则进行提示，若存在excel文件则循环读取所有的文件，利用实体类@Excel注解的方式读取excel的数据，将读取到的数据插入oracle数据库指定的表中

首先需要引入poi、poi-ooxml、commons-collections4、commons-lang3、commons-beanutils、oracle-jdbc驱动等相关依赖。

然后，可以编写一个ExcelUtil工具类，用于读取Excel文件并转换成对象列表：

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.text.DecimalFormat;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;

import org.apache.commons.beanutils.BeanUtils;
import org.apache.commons.collections4.CollectionUtils;
import org.apache.commons.lang3.StringUtils;
import org.apache.poi.hssf.usermodel.HSSFDateUtil;
import org.apache.poi.ss.usermodel.Cell;
import org.apache.poi.ss.usermodel.CellType;
import org.apache.poi.ss.usermodel.DateUtil;
import org.apache.poi.ss.usermodel.Row;
import org.apache.poi.ss.usermodel.Sheet;
import org.apache.poi.ss.usermodel.Workbook;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;

public class ExcelUtil {
    /**
     * 读取Excel文件并转换成对象列表
     * 
     * @param file Excel文件
     * @param clazz 对象类型
     * @return 对象列表
     */
    public static <T> List<T> readExcel(File file, Class<T> clazz) throws IOException {
        List<T> list = new ArrayList<>();
        try (InputStream is = new FileInputStream(file); Workbook workbook = new XSSFWorkbook(is)) {
            Sheet sheet = workbook.getSheetAt(0);
            if (sheet == null) {
                return list;
            }
            // 获取表头行
            Row headerRow = sheet.getRow(0);
            if (headerRow == null) {
                return list;
            }
            // 获取表头字段名
            List<String> headerFieldNames = new ArrayList<>();
            for (int i = 0; i < headerRow.getLastCellNum(); i++) {
                Cell cell = headerRow.getCell(i);
                if (cell == null || cell.getCellType() == CellType.BLANK) {
                    headerFieldNames.add(null);
                } else {
                    headerFieldNames.add(cell.getStringCellValue().trim());
                }
            }
            // 获取字段映射关系
            List<FieldMapping> fieldMappings = getFieldMappings(clazz, headerFieldNames);
            // 遍历每一行数据
            for (int i = 1; i <= sheet.getLastRowNum(); i++) {
                Row row = sheet.getRow(i);
                if (row == null) {
                    continue;
                }
                T obj = clazz.newInstance();
                // 遍历每一个单元格数据
                for (FieldMapping fieldMapping : fieldMappings) {
                    Cell cell = row.getCell(fieldMapping.getIndex());
                    if (cell == null || cell.getCellType() == CellType.BLANK) {
                        continue;
                    }
                    setFieldValue(obj, fieldMapping.getField(), cell);
                }
                list.add(obj);
            }
        } catch (Exception e) {
            throw new RuntimeException("Read Excel error", e);
        }
        return list;
    }

    /**
     * 获取字段映射关系
     * 
     * @param clazz 对象类型
     * @param headerFieldNames 表头字段名列表
     * @return 字段映射关系列表
     */
    private static List<FieldMapping> getFieldMappings(Class<?> clazz, List<String> headerFieldNames) {
        List<FieldMapping> fieldMappings = new ArrayList<>();
        for (Field field : clazz.getDeclaredFields()) {
            Excel excel = field.getAnnotation(Excel.class);
            if (excel == null) {
                continue;
            }
            String fieldName = StringUtils.isBlank(excel.fieldName()) ? field.getName() : excel.fieldName();
            int index = headerFieldNames.indexOf(fieldName);
            if (index < 0) {
                throw new RuntimeException("Excel header does not contain field: " + fieldName);
            }
            fieldMappings.add(new FieldMapping(field, index));
        }
        return fieldMappings;
    }

    /**
     * 设置对象字段值
     */
    private static void setFieldValue(Object obj, Field field, Cell cell) throws Exception {
        String cellValue = getCellValue(cell);
        Class<?> fieldType = field.getType();
        if (StringUtils.isBlank(cellValue)) {
            BeanUtils.setProperty(obj, field.getName(), null);
            return;
        }
        if (fieldType == String.class) {
            BeanUtils.setProperty(obj, field.getName(), cellValue);
        } else if (fieldType == Integer.TYPE || fieldType == Integer.class) {
            BeanUtils.setProperty(obj, field.getName(), Integer.parseInt(cellValue));
        } else if (fieldType == Long.TYPE || fieldType == Long.class) {
            BeanUtils.setProperty(obj, field.getName(), Long.parseLong(cellValue));
        } else if (fieldType == Float.TYPE || fieldType == Float.class) {
            BeanUtils.setProperty(obj, field.getName(), Float.parseFloat(cellValue));
        } else if (fieldType == Double.TYPE || fieldType == Double.class) {
            BeanUtils.setProperty(obj, field.getName(), Double.parseDouble(cellValue));
        } else if (fieldType == Date.class) {
            SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
            BeanUtils.setProperty(obj, field.getName(), sdf.parse(cellValue));
        } else {
            throw new RuntimeException("Unsupported field type: " + fieldType.getName());
        }
    }

    /**
     * 获取单元格值
     */
    private static String getCellValue(Cell cell) {
        if (cell == null) {
            return null;
        }
        DecimalFormat df = new DecimalFormat("#");
        switch (cell.getCellType()) {
        case STRING:
            return cell.getStringCellValue().trim();
        case NUMERIC:
            if (DateUtil.isCellDateFormatted(cell)) {
                Date date = HSSFDateUtil.getJavaDate(cell.getNumericCellValue());
                SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
                return sdf.format(date);
            } else {
                return df.format(cell.getNumericCellValue());
            }
        case BOOLEAN:
            return String.valueOf(cell.getBooleanCellValue());
        case FORMULA:
            return getCellValue(cell.getCachedFormulaResultType() == CellType.NUMERIC ? cell : cell.getSheet().getRow(cell.getRowIndex() + 1).getCell(cell.getColumnIndex()));
        default:
            return null;
        }
    }

    /**
     * 字段映射关系
     */
    private static class FieldMapping {
        private Field field;
        private int index;

        public FieldMapping(Field field, int index) {
            this.field = field;
            this.index = index;
        }

        public Field getField() {
            return field;
        }

        public int getIndex() {
            return index;
        }
    }
}

接着，可以定义一个Excel注解用于标记实体类的属性，以及一个扫描指定路径下Excel文件并插入数据库的方法：

import java.io.File;
import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.util.List;

public class ExcelDemo {
    @Excel(fieldName = "姓名")
    private String name;
    @Excel(fieldName = "年龄")
    private int age;
    @Excel(fieldName = "性别")
    private String gender;
    @Excel(fieldName = "职业")
    private String occupation;

    public static void main(String[] args) throws IOException {
        String excelDir = "path/to/excel/dir";
        String jdbcUrl = "jdbc:oracle:thin:@localhost:1521:orcl";
        String username = "username";
        String password = "password";
        File dir = new File(excelDir);
        if (!dir.exists() || !dir.isDirectory()) {
            System.out.println("Excel directory does not exist");
            return;
        }
        File[] files = dir.listFiles((dir1, name) -> name.toLowerCase().endsWith(".xlsx"));
        if (files == null || files.length == 0) {
            System.out.println("No Excel file found in directory");
            return;
        }
        try (Connection conn = DriverManager.getConnection(jdbcUrl, username, password)) {
            for (File file : files) {
                List<ExcelDemo> dataList = ExcelUtil.readExcel(file, ExcelDemo.class);
                if (CollectionUtils.isEmpty(dataList)) {
                    continue;
                }
                String sql = "INSERT INTO T_EXCEL_DEMO (NAME, AGE, GENDER, OCCUPATION) VALUES (?, ?, ?, ?)";
                try (PreparedStatement pstmt = conn.prepareStatement(sql)) {
                    for (ExcelDemo data : dataList) {
                        pstmt.setString(1, data.name);
                        pstmt.setInt(2, data.age);
                        pstmt.setString(3, data.gender);
                        pstmt.setString(4, data.occupation);
                        pstmt.executeUpdate();
                    }
                }
            }
        } catch (Exception e) {
            throw new RuntimeException("Insert data error", e);
        }
    }
}

其中，@Excel注解可以用于标记实体类的属性，指定其对应的Excel表头字段名：

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface Excel {
    String fieldName();
}