java.sql.SQLException: No value specified for parameter 1 異常分析

錯誤原始碼 java.sql.SQLException: No value specified for parameter 1，因為執行executeQuery()先於對sql語句中的佔位符賦值

    @Test
    public void test2() {
        InputStream is = null;
        FileOutputStream fos = null;
        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet rs = null;
        try {
            conn = JDBCUtils.getConnection();
            String sql = "select id,name,email,birth,photo from customers where id = ?";
            ps = conn.prepareStatement(sql);
            
//            ps.setInt(1,23);
            
            rs = ps.executeQuery();
            if (rs.next()) {
                int id = rs.getInt("id");
                String name = rs.getString("name");
                String email = rs.getString("email");
                Date birth = rs.getDate("birth");

                Customers customers = new Customers(id, name, email, birth);
                System.out.println(customers);
                //將Blob型別的欄位下載下來，以檔案的方式儲存在本地
                Blob photo = rs.getBlob("photo");
                is = photo.getBinaryStream();

                fos = new FileOutputStream("erxiong.jpg");
                byte[] buffer = new byte[1024];
                int len;
                while ((len = is.read(buffer)) != -1) {
                    fos.write(buffer, 0, len);
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                if (is != null)
                    is.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
            try {
                if (fos != null)
                    fos.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
            JDBCUtils.closeResource(conn, ps, rs);
        }
    }

修改後，執行executeQuery（）方法之前，先填寫佔位符

    @Test
    public void test2() {
        InputStream is = null;
        FileOutputStream fos = null;
        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet rs = null;
        try {
            conn = JDBCUtils.getConnection();
            String sql = "select id,name,email,birth,photo from customers where id = ?";
            ps = conn.prepareStatement(sql);
            //先對sql佔位符進行賦值
            ps.setInt(1,23);
            
            rs = ps.executeQuery();
            if (rs.next()) {
                int id = rs.getInt("id");
                String name = rs.getString("name");
                String email = rs.getString("email");
                Date birth = rs.getDate("birth");

                Customers customers = new Customers(id, name, email, birth);
                System.out.println(customers);
                //將Blob型別的欄位下載下來，以檔案的方式儲存在本地
                Blob photo = rs.getBlob("photo");
                is = photo.getBinaryStream();

                fos = new FileOutputStream("erxiong.jpg");
                byte[] buffer = new byte[1024];
                int len;
                while ((len = is.read(buffer)) != -1) {
                    fos.write(buffer, 0, len);
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                if (is != null)
                    is.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
            try {
                if (fos != null)
                    fos.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
            JDBCUtils.closeResource(conn, ps, rs);
        }
    }