實現簡單JDBC工具類

實現簡單JDBC工具類

1、查詢對象列表

public ArrayList getList(Class clazz) {
        ArrayList arrayList = new ArrayList();
        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet rs = null;
        try {
            conn = JDBCUtils.getConn();
            Field [] fields = clazz.getDeclaredFields();
            List<String> colList = getAllColumns(clazz.getSimpleName());
            StringBuilder sql = new StringBuilder("select ");
            for (int i = 0; i < colList.size(); i++) {
                sql.append(colList.get(i));
                if (i != colList.size() - 1) {
                    sql.append(", ");
                }
            }
            sql.append(" from ").append(clazz.getSimpleName());
            ps = conn.prepareStatement(sql.toString());
            rs = ps.executeQuery();
            while (rs.next()) {
                Object obj = clazz.newInstance();
                for (int i = 0; i < fields.length; i++) {
                    if (colList.contains(fields[i].getName())) {
                        fields[i].setAccessible(true);
                        fields[i].set(obj, rs.getObject(fields[i].getName()));
                    }
                }
                arrayList.add(obj);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.closeRes(conn, ps, rs);
        }
        return arrayList;
    }

2、查詢單個對象

public Object getOne(Class clazz, int id) {
        Object obj = null;
        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet rs = null;
        try {
            conn = JDBCUtils.getConn();
            Field [] fields = clazz.getDeclaredFields();
            List<String> colList = getAllColumns(clazz.getSimpleName());
            StringBuilder sql = new StringBuilder("select ");
            for (int i = 0; i < colList.size(); i++) {
                sql.append(colList.get(i));
                if (i != colList.size() - 1) {
                    sql.append(", ");
                }
            }
            sql.append(" from ").append(clazz.getSimpleName());
            sql.append(" where ").append(colList.get(0)).append(" = ? ");
            ps = conn.prepareStatement(sql.toString());
            ps.setObject(1, id);
            rs = ps.executeQuery();
            while (rs.next()) {
                obj = clazz.newInstance();
                for (int i = 0; i < fields.length; i++) {
                    if (colList.contains(fields[i].getName())) {
                        fields[i].setAccessible(true);
                        fields[i].set(obj, rs.getObject(fields[i].getName()));
                    }
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.closeRes(conn, ps, rs);
        }
        return obj;
    }

3、插入單個實體

public int insert(Object obj) {
        int res = -1;
        Connection conn = null;
        PreparedStatement ps = null;
        try {
            conn = JDBCUtils.getConn();
            Class clazz = obj.getClass();
            Field [] fields = clazz.getDeclaredFields();
            List<String> colList = getAllColumns(clazz.getSimpleName());
            StringBuilder sql = new StringBuilder("insert into ");
            sql.append(clazz.getSimpleName()).append(" (");
            for (int i = 0; i < fields.length; i++) {
                fields[i].setAccessible(true);
                sql.append(fields[i].getName());
                if (i != fields.length - 1) {
                    sql.append(", ");
                }
            }
            sql.append(") values (");
            for (int i = 0; i < fields.length; i++) {
                fields[i].setAccessible(true);
                sql.append(" ?");
                if (i != fields.length - 1) {
                    sql.append(", ");
                }
            }
            sql.append(")");
            ps = conn.prepareStatement(sql.toString());
            int j = 0;
            for (int i = 0; i < fields.length; i++) {
                j = i + 1;
                if (colList.contains(fields[i].getName())) {
                    fields[i].setAccessible(true);
                    // 這裏注意，佔位符從1開始，不是從0開始
                    ps.setObject(j, fields[i].get(obj));
                }
            }
            res = ps.executeUpdate();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.closeRes(conn, ps);
        }
        return res;
    }

4、更新單個實體

public int update(Object obj) {
        int res = -1;
        Connection conn = null;
        PreparedStatement ps = null;
        try {
            conn = JDBCUtils.getConn();
            Class clazz = obj.getClass();
            Field [] fields = clazz.getDeclaredFields();
            List<String> colList = getAllColumns(clazz.getSimpleName());
            StringBuilder sql = new StringBuilder("update ");
            sql.append(clazz.getSimpleName());
            sql.append(" set ");
            for (int i = 1; i < fields.length; i++) {
                fields[i].setAccessible(true);
                sql.append(fields[i].getName()).append(" = ? ");
                if (i != fields.length - 1) {
                    sql.append(", ");
                }
            }
            sql.append(" where ");
            sql.append(fields[0].getName()).append(" = ?");
            ps = conn.prepareStatement(sql.toString());
            for (int i = 1; i < fields.length; i++) {
                if (colList.contains(fields[i].getName())) {
                    fields[i].setAccessible(true);
                    // 這裏注意，佔位符從1開始，不是從0開始
                    ps.setObject(i, fields[i].get(obj));
                }
            }
            // id的位置
            int idIndex = 0;
            fields[idIndex].setAccessible(true);
            ps.setObject(fields.length, fields[idIndex].get(obj));
            res = ps.executeUpdate();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.closeRes(conn, ps);
        }
        return res;
    }

5、根據id刪除

public int delete(Class clazz, int id) {
        int res = -1;
        Connection conn = null;
        PreparedStatement ps = null;
        try {
            conn = JDBCUtils.getConn();
            Field [] fields = clazz.getDeclaredFields();
            int idIndex = 0;
            int paramIndex = 1;
            StringBuilder sql = new StringBuilder("delete from ");
            sql.append(clazz.getSimpleName()).append(" where ");
            sql.append(fields[idIndex].getName()).append(" = ? ");
            ps = conn.prepareStatement(sql.toString());
            ps.setObject(paramIndex, id);
            res = ps.executeUpdate();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.closeRes(conn, ps);
        }
        return res;
    }

以上方法都是按照數據庫字段和實體類屬性對應的基礎上實現的通用方法，一旦數據庫的字段與實體類屬性不一致的時候，以上的工具類方法便失效了，這時候，就會出現如hibernate或者jpa的配置實體類映射文件或者註解的方式實現的實體類屬性和數據庫表字段的一一對應。

最後附上代碼地址：https://gitee.com/bzjl/learning/tree/master/