【Java高级篇】基于反射+注解实现抽象JDBC工具类BaseDao

业界资讯 2023-08-13 03:41:51 阅读次数: 0

【Java高级篇】基于反射+注解实现抽象JDBC工具类BaseDao

Pom

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.11</version>
</dependency>

注解

@TableName

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface TableName {
    
    
    String value();
}

@Id

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

@Column

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface Column {
    
    
    /**
     * 字段名称
     */
    String value();
    /**
     * 字段的类型
     * @return
     */
    Class<?> type() default String.class;
    /**
     * 字段的长度
     * @return
     */
    int length() default 0;
}

抽象Dao层

BaseDao

public interface BaseDao<T> {
    
    


    void save(T t) throws Exception;

    void deleteById(Object id, Class<T> clazz) throws Exception;

    void updateById(T t) throws Exception;

    T getById(Object id, Class<T> clazz) throws Exception;

    /**
     * 根据条件查询
     *
     * @param sqlWhereMap key：条件字段名 value：条件字段值
     * @param clazz
     * @return
     * @throws Exception
     */
    List<T> findAllByConditions(Map<String, Object> sqlWhereMap, Class<T> clazz) throws Exception;
}

BaseDaoImpl

import java.beans.IntrospectionException;
import java.beans.PropertyDescriptor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.sql.*;
import java.util.*;
import java.util.Date;

public abstract class BaseDaoImpl<T> implements BaseDao<T> {
    
    

    //表的别名
    private static final String TABLE_ALIAS = "t";

    @Override
    public void save(T t) throws Exception {
    
    
        Class<?> clazz = t.getClass();
        //获得表名
        String tableName = getTableName(clazz);
        //获得字段
        StringBuilder fieldNames = new StringBuilder();        //字段名
        List<Object> fieldValues = new ArrayList<Object>();    //字段值
        StringBuilder placeholders = new StringBuilder();    //占位符

        Field[] fields = clazz.getDeclaredFields();
        for (Field field : fields) {
    
    
            PropertyDescriptor pd = new PropertyDescriptor(field.getName(), clazz);
            if (field.isAnnotationPresent(Id.class)) {
    
    
                fieldNames.append(field.getAnnotation(Id.class).value()).append(",");
                fieldValues.add(pd.getReadMethod().invoke(t));
            } else if (field.isAnnotationPresent(Column.class)) {
    
    
                fieldNames.append(field.getAnnotation(Column.class).value()).append(",");
                fieldValues.add(pd.getReadMethod().invoke(t));
            }
            placeholders.append("?").append(",");
        }
        //删除最后一个逗号
        fieldNames.deleteCharAt(fieldNames.length() - 1);
        placeholders.deleteCharAt(placeholders.length() - 1);
        //拼接sql
        StringBuilder sql = new StringBuilder("");
        sql.append("insert into ").append(tableName)
                .append(" (").append(fieldNames.toString())
                .append(") values (").append(placeholders).append(")");
        PreparedStatement ps = JdbcDaoHelper.getConnection().prepareStatement(sql.toString());
        //设置SQL参数占位符的值
        setParameter(fieldValues, ps, false);
        //执行SQL
        ps.execute();
        JdbcDaoHelper.release(ps, null);
        System.out.println(sql + "\n" + clazz.getSimpleName() + "添加成功!");
    }

    @Override
    public void deleteById(Object id, Class<T> clazz) throws Exception {
    
    
        //获得表名
        String tableName = getTableName(clazz);
        //获得ID字段名和值
        String idFieldName = "";
        boolean flag = false;
        Field[] fields = clazz.getDeclaredFields();
        for (Field field : fields) {
    
    
            if (field.isAnnotationPresent(Id.class)) {
    
    
                idFieldName = field.getAnnotation(Id.class).value();
                flag = true;
                break;
            }
        }
        if (!flag) {
    
    
            throw new NotFoundAnnotationException(clazz.getName() + " object not found id property.");
        }
        //拼装sql
        String sql = "delete from " + tableName + " where " + idFieldName + "=?";
        PreparedStatement ps = JdbcDaoHelper.getConnection().prepareStatement(sql);
        ps.setObject(1, id);
        //执行SQL
        ps.execute();
        JdbcDaoHelper.release(ps, null);
        System.out.println(sql + "\n" + clazz.getSimpleName() + "删除成功!");
    }

    @Override
    public void updateById(T t) throws Exception {
    
    
        Class<?> clazz = t.getClass();
        //获得表名
        String tableName = getTableName(clazz);
        //获得字段
        List<Object> fieldNames = new ArrayList<Object>();    //字段名
        List<Object> fieldValues = new ArrayList<Object>();    //字段值
        List<String> placeholders = new ArrayList<String>();//占位符
        String idFieldName = "";
        Object idFieldValue = "";
        Field[] fields = clazz.getDeclaredFields();
        for (Field field : fields) {
    
    
            PropertyDescriptor pd = new PropertyDescriptor(field.getName(), t.getClass());
            if (field.isAnnotationPresent(Id.class)) {
    
    
                if (Objects.isNull(pd.getReadMethod().invoke(t))) {
    
    
                    throw new RuntimeException(field.getName() + " Value cannot be empty.");
                }
                idFieldName = field.getAnnotation(Id.class).value();
                idFieldValue = pd.getReadMethod().invoke(t);
            } else if (field.isAnnotationPresent(Column.class)) {
    
    
                if (Objects.nonNull(pd.getReadMethod().invoke(t))) {
    
    
                    fieldNames.add(field.getAnnotation(Column.class).value());
                    fieldValues.add(pd.getReadMethod().invoke(t));
                    placeholders.add("?");
                }
            }
        }
        //ID作为更新条件，放在集合中的最后一个元素
        fieldNames.add(idFieldName);
        fieldValues.add(idFieldValue);
        placeholders.add("?");
        //拼接sql
        StringBuilder sql = new StringBuilder("");
        sql.append("update ").append(tableName).append(" set ");
        int index = fieldNames.size() - 1;
        for (int i = 0; i < index; i++) {
    
    
            sql.append(fieldNames.get(i)).append("=").append(placeholders.get(i)).append(",");
        }
        sql.deleteCharAt(sql.length() - 1).append(" where ").append(fieldNames.get(index)).append("=").append("?");
        //设置SQL参数占位符的值
        PreparedStatement ps = JdbcDaoHelper.getConnection().prepareStatement(sql.toString());
        setParameter(fieldValues, ps, false);
        //执行SQL
        ps.execute();
        JdbcDaoHelper.release(ps, null);
        System.out.println(sql + "\n" + clazz.getSimpleName() + "修改成功.");
    }

    @Override
    public T getById(Object id, Class<T> clazz) throws Exception {
    
    
        String idFieldName = "";
        Field[] fields = clazz.getDeclaredFields();
        boolean flag = false;
        for (Field field : fields) {
    
    
            if (field.isAnnotationPresent(Id.class)) {
    
    
                idFieldName = field.getAnnotation(Id.class).value();
                flag = true;
                break;
            }
        }
        if (!flag) {
    
    
            throw new NotFoundAnnotationException(clazz.getName() + " object not found id property.");
        }
        //拼装SQL
        Map<String, Object> sqlWhereMap = new HashMap<String, Object>();
        sqlWhereMap.put(TABLE_ALIAS + "." + idFieldName, id);
        List<T> list = findAllByConditions(sqlWhereMap, clazz);
        return list.size() > 0 ? list.get(0) : null;
    }

    @Override
    public List<T> findAllByConditions(Map<String, Object> sqlWhereMap, Class<T> clazz) throws Exception {
    
    
        List<T> list = new ArrayList<T>();
        String tableName = getTableName(clazz);
        String idFieldName = "";
        //存储所有字段的信息
        //通过反射获得要查询的字段
        StringBuffer fieldNames = new StringBuffer();
        Field[] fields = clazz.getDeclaredFields();
        for (Field field : fields) {
    
    
            String propertyName = field.getName();
            if (field.isAnnotationPresent(Id.class)) {
    
    
                idFieldName = field.getAnnotation(Id.class).value();
                fieldNames.append(TABLE_ALIAS + "." + idFieldName)
                        .append(" as ").append(propertyName).append(",");
            } else if (field.isAnnotationPresent(Column.class)) {
    
    
                fieldNames.append(TABLE_ALIAS + "." + field.getAnnotation(Column.class).value())
                        .append(" as ").append(propertyName).append(",");
            }
        }
        fieldNames.deleteCharAt(fieldNames.length() - 1);
        //拼装SQL
        String sql = "select " + fieldNames + " from " + tableName + " " + TABLE_ALIAS;
        PreparedStatement ps = null;
        List<Object> values = null;
        if (sqlWhereMap != null) {
    
    
            List<Object> sqlWhereWithValues = getSqlWhereWithValues(sqlWhereMap);
            if (sqlWhereWithValues != null) {
    
    
                //拼接SQL条件
                String sqlWhere = (String) sqlWhereWithValues.get(0);
                sql += sqlWhere;
                //得到SQL条件中占位符的值
                values = (List<Object>) sqlWhereWithValues.get(1);
            }
        }
        //设置参数占位符的值
        if (values != null) {
    
    
            ps = JdbcDaoHelper.getConnection().prepareStatement(sql);
            setParameter(values, ps, true);
        } else {
    
    
            ps = JdbcDaoHelper.getConnection().prepareStatement(sql);
        }
        //执行SQL
        ResultSet rs = ps.executeQuery();
        while (rs.next()) {
    
    
            T t = clazz.newInstance();
            initObject(t, fields, rs);
            list.add(t);
        }
        //释放资源
        JdbcDaoHelper.release(ps, rs);
        System.out.println(sql);
        return list;
    }

    /**
     * 根据结果集初始化对象
     */
    private void initObject(T t, Field[] fields, ResultSet rs)
            throws SQLException, IntrospectionException,
            IllegalAccessException, InvocationTargetException, IntrospectionException {
    
    
        for (Field field : fields) {
    
    
            String propertyName = field.getName();
            Object paramVal = null;
            Class<?> clazzField = field.getType();
            if (clazzField == String.class) {
    
    
                paramVal = rs.getString(propertyName);
            } else if (clazzField == short.class || clazzField == Short.class) {
    
    
                paramVal = rs.getShort(propertyName);
            } else if (clazzField == int.class || clazzField == Integer.class) {
    
    
                paramVal = rs.getInt(propertyName);
            } else if (clazzField == long.class || clazzField == Long.class) {
    
    
                paramVal = rs.getLong(propertyName);
            } else if (clazzField == float.class || clazzField == Float.class) {
    
    
                paramVal = rs.getFloat(propertyName);
            } else if (clazzField == double.class || clazzField == Double.class) {
    
    
                paramVal = rs.getDouble(propertyName);
            } else if (clazzField == boolean.class || clazzField == Boolean.class) {
    
    
                paramVal = rs.getBoolean(propertyName);
            } else if (clazzField == byte.class || clazzField == Byte.class) {
    
    
                paramVal = rs.getByte(propertyName);
            } else if (clazzField == char.class || clazzField == Character.class) {
    
    
                paramVal = rs.getCharacterStream(propertyName);
            } else if (clazzField == Date.class) {
    
    
                paramVal = rs.getTimestamp(propertyName);
            } else if (clazzField.isArray()) {
    
    
                paramVal = rs.getString(propertyName).split(",");    //以逗号分隔的字符串
            }
            PropertyDescriptor pd = new PropertyDescriptor(propertyName, t.getClass());
            pd.getWriteMethod().invoke(t, paramVal);
        }
    }

    /**
     * 根据条件，返回sql条件和条件中占位符的值
     *
     * @param sqlWhereMap key：字段名 value：字段值
     * @return 第一个元素为SQL条件，第二个元素为SQL条件中占位符的值
     */
    private List<Object> getSqlWhereWithValues(Map<String, Object> sqlWhereMap) {
    
    
        if (sqlWhereMap.size() < 1) return null;
        List<Object> list = new ArrayList<Object>();
        List<Object> fieldValues = new ArrayList<Object>();
        StringBuffer sqlWhere = new StringBuffer(" where ");
        Set<Map.Entry<String, Object>> entrySets = sqlWhereMap.entrySet();
        for (Iterator<Map.Entry<String, Object>> iteraotr = entrySets.iterator(); iteraotr.hasNext(); ) {
    
    
            Map.Entry<String, Object> entrySet = iteraotr.next();
            fieldValues.add(entrySet.getValue());
            Object value = entrySet.getValue();
            if (value.getClass() == String.class) {
    
    
                sqlWhere.append(entrySet.getKey()).append(" like ").append("?").append(" and ");
            } else {
    
    
                sqlWhere.append(entrySet.getKey()).append("=").append("?").append(" and ");
            }
        }
        sqlWhere.delete(sqlWhere.lastIndexOf("and"), sqlWhere.length());
        list.add(sqlWhere.toString());
        list.add(fieldValues);
        return list;
    }

    /**
     * 获得表名
     */
    private String getTableName(Class<?> clazz) throws NotFoundAnnotationException {
    
    
        if (clazz.isAnnotationPresent(TableName.class)) {
    
    
            TableName entity = clazz.getAnnotation(TableName.class);
            return entity.value();
        } else {
    
    
            throw new NotFoundAnnotationException(clazz.getName() + " is not Entity Annotation.");
        }
    }

    /**
     * 设置SQL参数占位符的值
     */
    private void setParameter(List<Object> values, PreparedStatement ps, boolean isSearch) throws SQLException {
    
    
        for (int i = 1; i <= values.size(); i++) {
    
    
            Object fieldValue = values.get(i - 1);
            Class<?> clazzValue = fieldValue.getClass();
            if (clazzValue == String.class) {
    
    
                if (isSearch)
                    ps.setString(i, "%" + (String) fieldValue + "%");
                else
                    ps.setString(i, (String) fieldValue);
            } else if (clazzValue == boolean.class || clazzValue == Boolean.class) {
    
    
                ps.setBoolean(i, (Boolean) fieldValue);
            } else if (clazzValue == byte.class || clazzValue == Byte.class) {
    
    
                ps.setByte(i, (Byte) fieldValue);
            } else if (clazzValue == char.class || clazzValue == Character.class) {
    
    
                ps.setObject(i, fieldValue, Types.CHAR);
            } else if (clazzValue == Date.class) {
    
    
                ps.setTimestamp(i, new Timestamp(((Date) fieldValue).getTime()));
            } else if (clazzValue.isArray()) {
    
    
                Object[] arrayValue = (Object[]) fieldValue;
                StringBuffer sb = new StringBuffer();
                for (int j = 0; j < arrayValue.length; j++) {
    
    
                    sb.append(arrayValue[j]).append("、");
                }
                ps.setString(i, sb.deleteCharAt(sb.length() - 1).toString());
            } else {
    
    
                ps.setObject(i, fieldValue, Types.NUMERIC);
            }
        }
    }
}

JdbcDaoHelper

public class JdbcDaoHelper {
    
    
    /**
     * 数据库用户名
     */
    private static final String USER = "root";
    /**
     * 数据库密码
     */
    private static final String PASSWORD = "root";
    /**
     * 连接数据库的地址
     */
    private static final String URL = "jdbc:mysql://localhost:3306/study_db?useUnicode=true&characterEncoding=utf-8&serverTimezone=UTC";
    private static Connection conn;
    /**
     * 获得一个数据库连接对象
     * @return java.sql.Connection实例
     */
    public static Connection getConnection() {
    
    
        try {
    
    
            if (conn == null) {
    
    
                Class.forName("com.mysql.cj.jdbc.Driver");
                conn = DriverManager.getConnection(URL, USER, PASSWORD);
            } else {
    
    
                return conn;
            }
        } catch (Exception e) {
    
    
            e.printStackTrace();
        }
        return conn;
    }
    /**
     * 释放数据库资源
     */
    public static void release(PreparedStatement ps, ResultSet rs) {
    
    
        try {
    
    
            if (conn != null) {
    
    
                conn.close();
                conn = null;
            }
            if (ps != null) {
    
    
                ps.close();
                ps = null;
            }
            if (rs != null) {
    
    
                rs.close();
                rs = null;
            }
        } catch (SQLException e) {
    
    
            e.printStackTrace();
        }
    }
}

测试

Person

@TableName("t_person")
public class Person {
    
    

    @Id("id")
    private Long id;

    @Column("t_isbn")
    private String isbn;
    /**
     * 书名
     */
    @Column("t_name")
    private String name;
    /**
     * 出版时间
     */
    @Column(value = "t_pubdate")
    private Date pubdate;
    /**
     * 价格
     */
    @Column(value = "t_price")
    private double price;

    public String getIsbn() {
    
    
        return isbn;
    }

    public void setIsbn(String isbn) {
    
    
        this.isbn = isbn;
    }

    public String getName() {
    
    
        return name;
    }

    public void setName(String name) {
    
    
        this.name = name;
    }

    public Date getPubdate() {
    
    
        return pubdate;
    }

    public void setPubdate(Date pubdate) {
    
    
        this.pubdate = pubdate;
    }

    public double getPrice() {
    
    
        return price;
    }

    public void setPrice(double price) {
    
    
        this.price = price;
    }

    public Long getId() {
    
    
        return id;
    }

    public void setId(Long id) {
    
    
        this.id = id;
    }

    @Override
    public String toString() {
    
    
        return "Person{" +
                "id=" + id +
                ", isbn='" + isbn + '\'' +
                ", name='" + name + '\'' +
                ", pubdate=" + pubdate +
                ", price=" + price +
                '}';
    }
}

PersonService

public interface PersonService {
    
    
}

PersonServiceImpl

public class PersonServiceImpl extends BaseDaoImpl<Person> implements PersonService {
    
    
}

PersonTest

public static void main(String[] args) throws Exception {
    
    
        PersonServiceImpl personService = new PersonServiceImpl();
//        Person savePerson = new Person();
//        savePerson.setId(1001L);
//        savePerson.setIsbn("zyshepp");
//        savePerson.setName("打篮球");
//        savePerson.setPubdate(new Date());
//        savePerson.setPrice(90);
//        personService.save(savePerson);

       // personService.deleteById(1001, Person.class);


//        Person upPerson = new Person();
//        upPerson.setId(1001L);
//        upPerson.setIsbn("zyshepp");
//        upPerson.setName("唱、跳、rap");
//        upPerson.setPubdate(new Date());
//        upPerson.setPrice(190);
//        personService.updateById(upPerson);


    //    System.out.println(personService.getById(1001, Person.class));

        HashMap<String, Object> hashMap = new HashMap<>();

        hashMap.put("t_name", "唱、跳、rap");

        System.out.println(personService.findAllByConditions(hashMap, Person.class));
    }
}

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