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。
原文地址：https://www.cnblogs.com/ztbk/p/11053543.html
时间： 2024-10-10 02:14:49