通用分页1

通用分页

首先你得先把数据库连上（由于数据库不同，就不做演示了）

然后就是准备一个判断字符串得类

StringUtils类

public class StringUtils {
    // 私有的构造方法，保护此类不能在外部实例化
    private StringUtils() {
    }

    /**
     * 如果字符串等于null或去空格后等于""，则返回true，否则返回false
     * 
     * @param s
     * @return
     */
    public static boolean isBlank(String s) {
        boolean b = false;
        if (null == s || s.trim().equals("")) {
            b = true;
        }
        return b;
    }
    
    /**
     * 如果字符串不等于null或去空格后不等于""，则返回true，否则返回false
     * 
     * @param s
     * @return
     */
    public static boolean isNotBlank(String s) {
        return !isBlank(s);
    }

}

其次实体类是必不可少的

book

public class Book {
    private int bid;
    private String bname;
    private float price;

    @Override
    public String toString() {
        return "Book [bid=" + bid + ", bname=" + bname + ", price=" + price + "]";
    }

    public int getBid() {
        return bid;
    }

    public void setBid(int bid) {
        this.bid = bid;
    }

    public String getBname() {
        return bname;
    }

    public void setBname(String bname) {
        this.bname = bname;
    }

    public float getPrice() {
        return price;
    }

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

    public Book(int bid, String bname, float price) {
        super();
        this.bid = bid;
        this.bname = bname;
        this.price = price;
    }

    public Book() {
        super();
        // TODO Auto-generated constructor stub
    }
    

}

通用分页还需要一个工具类pagebean

public class PageBean {

    private int page = 1;// 页码

    private int rows = 10;// 页大小

    private int total = 0;// 总记录数

    private boolean pagination = true;// 是否分页

    public PageBean() {
        super();
    }

    public int getPage() {
        return page;
    }

    public void setPage(int page) {
        this.page = page;
    }

    public int getRows() {
        return rows;
    }

    public void setRows(int rows) {
        this.rows = rows;
    }

    public int getTotal() {
        return total;
    }

    public void setTotal(int total) {
        this.total = total;
    }

    public void setTotal(String total) {
        this.total = Integer.parseInt(total);
    }

    public boolean isPagination() {
        return pagination;
    }

    public void setPagination(boolean pagination) {
        this.pagination = pagination;
    }

    /**
     * 获得起始记录的下标
     * 
     * @return
     */
    public int getStartIndex() {
        return (this.page - 1) * this.rows;
    }

    @Override
    public String toString() {
        return "PageBean [page=" + page + ", rows=" + rows + ", total=" + total + ", pagination=" + pagination + "]";
    }

}

 

接下来就是basedao使用泛型

basedao

public class BaseDao<T> {
    
    public List<T> executeQuery(String sql,Class clz,PageBean pageBean) throws SQLException, InstantiationException, IllegalAccessException{
        Connection con=DBAccess.getConnection();
        PreparedStatement pst=null;
        ResultSet rs=null;
        if(pageBean!=null&&pageBean.isPagination()) {
            //需要分页
            //算符合条件的总记录数
            String countsql=getcountsql(sql);
            pst=con.prepareStatement(countsql);
            rs=pst.executeQuery();
            if(rs.next()) {
                pageBean.setTotal(rs.getLong(1)+"");
            }
            //查询出符合条件的结果集
            String pageSql=getPageSql(sql,pageBean);
            pst=con.prepareStatement(pagesql);
            rs=pst.executeQuery();
        }else {
            pst=con.prepareStatement(sql);
            rs=pst.executeQuery();
        }
        List<T> list=new ArrayList<>();
        T t;
        while(rs.next()) {
            /*
             * 1，实例化一个book对象(该对象是空得)
             * 2，取book得所有属性，然后给其赋值
             * 2.1获取所有属性对象
             * 2.2给属性对象赋值
             * 3，赋完值得book对象装进list容器中
             */
//            list.add(new Book(rs.getInt("bid"),rs.getString("bname"),rs.getFloat("price")));
            t=(T) clz.newInstance();
            Field[] fields= clz.getDeclaredFields();
            for (Field field : fields) {
                field.setAccessible(true);
                field.set(t, rs.getObject(field.getName()));
            }
            list.add(t);
        }
        DBAccess.close(con, pst, rs);
        return list;
    }
    /**
     * 利用原生sql拼接出符合条件的结果集的查询sql
     * @param sql
     * @param pageBean
     * @return
     */
    private String getPageSql(String sql, PageBean pageBean) {
        // TODO Auto-generated method stub
        return sql+" limit "+pageBean.getStartIndex()+",5";
    }
    /**
     * 获取符合条件的总记录
     * @param sql
     * @return
     */
    private String getcountsql(String sql) {
        // TODO Auto-generated method stub
        return "SELECT COUNT(*)FROM("+sql+")t;";
    }
}

接下来就是我们的dao方法了，写完dao方法就可以直接运行看看效果了

public class BookDao extends BaseDao<Book> {
    
    public List<Book> list(Book book, PageBean pageBean)
            throws SQLException, InstantiationException, IllegalAccessException {
        String sql = "select * from t_mvc_book where true";
        String bname = book.getBname();
        if (StringUtils.isNotBlank(bname)) {
            sql += " and bname like '%" + bname + "%'";
        }
        return super.executeQuery(sql, Book.class, pageBean);
    }
    public static void main(String[] args) throws InstantiationException, IllegalAccessException, SQLException {
        BookDao bookDao = new BookDao();
        
            
            Book book = new Book();
            PageBean pageBean = new PageBean();
            book.setBname("圣墟");
            pageBean.setPage(2);//这是是设置看第几页的
            List<Book> list = bookDao.list(book, pageBean);
            for (Book b : list) {
                System.out.println(b);
            }
        
        
    }
}

结果（这是我设置pageBean.setPage(2);）只要要改括号，改变查询的页数

 下面还做了一个小测试，看查其他的表需要写多少代码可以实现这个分页

建一个实体类blog类

public class Blog {
     private int id;
     private String bookname;
  
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getBookname() {
        return bookname;
    }
    public void setBookname(String bookname) {
        this.bookname = bookname;
    }
    @Override
    public String toString() {
        return "Blog [id=" + id + ", bookname=" + bookname + "]";
    }
}

接下来直接写dao方法继承下basedao就可以了

public class BlogDao extends BaseDao<Blog> {

    public List<Blog> list(Blog blog, PageBean pageBean)throws SQLException, InstantiationException, IllegalAccessException {
        String sql = "select * from t_book where true";
        String bookname = blog.getBookname();
        if (StringUtils.isNotBlank(bookname)) {
            sql += " and bookname LIKE '%" + bookname + "%'";
        }
        System.out.println(sql);
        return super.executeQuery(sql, Blog.class, pageBean);
    }

    public static void main(String[] args) throws InstantiationException, IllegalAccessException, SQLException {
        BlogDao blogDao = new BlogDao();
        PageBean pageBean = new PageBean();
        Blog blog = new Blog();
        blog.setBookname("哈林");
        pageBean.setPage(3);
        List<Blog> list = blogDao.list(blog, pageBean);
        for (Blog b : list) {
            System.out.println(b);
        }

    }
}

让我们来看下结果，这就完成了

 这就实现了分页效果，就是这么简单了，直接一套用就可以了，简化代码真的实用。