通用分页
思路：
- 将原有的查询向上抽取
- 让返回值变成泛型
- 使用回调函数处理resultset
- 利用反射处理回调函数
- 获取总记录数（页面展示，计算总页数）
- 拼接分页sql语句，获取对应的结果集
需要导入的jar包：
首先连接数据库：
连接数据库类：
package com.xhh.util;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Properties;
/**
* 提供了一组获得或关闭数据库对象的方法
*
*/
public class DBAccess {
private static String driver;
private static String url;
private static String user;
private static String password;
static {// 静态块执行一次，加载 驱动一次
try {
InputStream is = DBAccess.class
.getResourceAsStream("config.properties");
Properties properties = new Properties();
properties.load(is);
driver = properties.getProperty("driver");
url = properties.getProperty("url");
user = properties.getProperty("user");
password = properties.getProperty("pwd");
Class.forName(driver);
} catch (Exception e) {
e.printStackTrace();
throw new RuntimeException(e);
}
}
/**
* 获得数据连接对象
*
* @return
*/
public static Connection getConnection() {
try {
Connection conn = DriverManager.getConnection(url, user, password);
return conn;
} catch (SQLException e) {
e.printStackTrace();
throw new RuntimeException(e);
}
}
public static void close(ResultSet rs) {
if (null != rs) {
try {
rs.close();
} catch (SQLException e) {
e.printStackTrace();
throw new RuntimeException(e);
}
}
}
public static void close(Statement stmt) {
if (null != stmt) {
try {
stmt.close();
} catch (SQLException e) {
e.printStackTrace();
throw new RuntimeException(e);
}
}
}
public static void close(Connection conn) {
if (null != conn) {
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
throw new RuntimeException(e);
}
}
}
public static void close(Connection conn, Statement stmt, ResultSet rs) {
close(rs);
close(stmt);
close(conn);
}
public static boolean isOracle() {
return "oracle.jdbc.driver.OracleDriver".equals(driver);
}
public static boolean isSQLServer() {
return "com.microsoft.sqlserver.jdbc.SQLServerDriver".equals(driver);
}
public static boolean isMysql() {
return "com.mysql.jdbc.Driver".equals(driver);
}
public static void main(String[] args) {
Connection conn = DBAccess.getConnection();
DBAccess.close(conn);
System.out.println("isOracle：" + isOracle());
System.out.println("isSQLServer：" + isSQLServer());
System.out.println("isMysql：" + isMysql());
System.out.println("数据库连接(关闭)成功");
}
}
接下来还需要一个连接数据库config.properties文件：
#oracle9i
#driver=oracle.jdbc.driver.OracleDriver
#url=jdbc:oracle:thin:@localhost:1521:ora9
#user=test
#pwd=test
#sql2005
#driver=com.microsoft.sqlserver.jdbc.SQLServerDriver
#url=jdbc:sqlserver://localhost:1423;DatabaseName=test
#user=sa
#pwd=sa
#sql2000
#driver=com.microsoft.jdbc.sqlserver.SQLServerDriver
#url=jdbc:microsoft:sqlserver://localhost:1433;databaseName=unit6DB
#user=sa
#pwd=888888
#mysql5
driver=com.mysql.jdbc.Driver
url=jdbc:mysql://127.0.0.1:3306/xhh?useUnicode=true&characterEncoding=utf8&serverTimezone=GMT
user=root
pwd=123
本人用的是mysql数据库，需要注意的：
封装好了的PageBean分页的助手类：
分页三要素
page 页码 视图层传递过来
rows 页大小 视图层传递过来
total 总记录数 后台查出来
pagination 是否分页 视图层传递过来
原生sql:
select * from t_mvc_book where bname like ‘%斗破%’;
符合条件的记录数
select count(1) from (select * from t_mvc_book where bname like ‘%斗破%’) t;
分页的查询语句
select * from t_mvc_book where bname like ‘%斗破%’ limit start,offset
start 查询数据集的起始下标
offset：查询展示在当前页的记录
package com.xhh.util;
/**
* 分页工具类
*
*/
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 + "]";
}
}
处理中文乱码的助手类：EncodingFiter
package com.xhh.util;
import java.io.IOException;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* 中文乱码处理
*
*/
public class EncodingFiter implements Filter {
private String encoding = "UTF-8";// 默认字符集
public EncodingFiter() {
super();
}
public void destroy() {
}
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
HttpServletRequest req = (HttpServletRequest) request;
HttpServletResponse res = (HttpServletResponse) response;
// 中文处理必须放到 chain.doFilter(request, response)方法前面
res.setContentType("text/html;charset=" + this.encoding);
if (req.getMethod().equalsIgnoreCase("post")) {
req.setCharacterEncoding(this.encoding);
} else {
Map map = req.getParameterMap();// 保存所有参数名=参数值(数组)的Map集合
Set set = map.keySet();// 取出所有参数名
Iterator it = set.iterator();
while (it.hasNext()) {
String name = (String) it.next();
String[] values = (String[]) map.get(name);// 取出参数值[注：参数值为一个数组]
for (int i = 0; i < values.length; i++) {
values[i] = new String(values[i].getBytes("ISO-8859-1"),
this.encoding);
}
}
}
chain.doFilter(request, response);
}
public void init(FilterConfig filterConfig) throws ServletException {
String s = filterConfig.getInitParameter("encoding");// 读取web.xml文件中配置的字符集
if (null != s && !s.trim().equals("")) {
this.encoding = s.trim();
}
}
}
判断String是否为空的助手类：StringUtils
package com.xhh.util;
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);
}
}
然后测试连接数据库：
数据库连接成功了！
数据库表的实体类：Book
package com.xhh.entity;
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();
}
}
Dao包：
BookDao:
普通的查询
package com.xhh.Dao;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
import com.xhh.entity.Book;
import com.xhh.util.BaseDao;
import com.xhh.util.DBAccess;
import com.xhh.util.PageBean;
import com.xhh.util.StringUtils;
public class BookDao extends BaseDao<Book>{
/**
* 第一个版本
* 普通的查询（带条件）
* @param book 实体类
* @param pageBean 分页助手
* @return
* @throws SQLException
* @throws IllegalAccessException
* @throws InstantiationException
*/
public List<Book> list(Book book,PageBean pageBean) throws SQLException{
String sql="select * from t_mvc_book where true";
List<Book> list=new ArrayList<>();
String bname=book.getBname();
if(StringUtils.isNotBlank(bname)) {
sql +=" and bname like '%"+bname+"%'";
}
Connection con = DBAccess.getConnection();
PreparedStatement pst = con.prepareStatement(sql);
ResultSet rs = pst.executeQuery();
while(rs.next()) {
list.add(new Book(rs.getInt("bid"),rs.getString("bname"),rs.getFloat("price")));
}
return list;
}
//测试 普通的查询
public static void main(String[] args) {
BookDao bookDao = new BookDao();
Book book = new Book();
try {
book.setBname("圣墟");
List<Book> list = bookDao.list(book, null);
for (Book b : list) {
System.out.println(b);
}
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
运行结果：
将普通查询方法封装起来，重复使用，减少没必要的代码量
BaseDao:
package com.xhh.util;
import java.lang.reflect.Field;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
import com.xhh.entity.Book;
public class BaseDao<T> {
/**
* @param sql 可能不同的表，那么意味着sql是变化的，那么它是从子类处理好在传递到父类
* @param clz 需要返回不同的对象集合 Book.class/Order.class
* @param pageBean 可能要分页
* @return
* @throws SQLException
* @throws IllegalAccessException
* @throws InstantiationException
*/
public List<T> executeQuery(String sql,Class clz,PageBean pageBean) throws SQLException, InstantiationException, IllegalAccessException{
List<T> list=new ArrayList<>();
Connection con = DBAccess.getConnection();
PreparedStatement pst = con.prepareStatement(sql);
ResultSet rs = pst.executeQuery();
T t=null;
while(rs.next()) {
// list.add(new Book(rs.getInt("bid"),rs.getString("bname"),rs.getFloat("price")));
/*
* 1.实例化一个book对象 null
* 2.通过book对象的属性名去游标中取出属性值
* 2.1.获取到类对象中的属性
* 2.2.给属性复制
* 3.已经赋值好的book实例对象，放入book中
*/
t=(T) clz.newInstance();
Field[] fields = clz.getDeclaredFields();
for (Field f : fields) {
f.setAccessible(true);
f.set(t, rs.getObject(f.getName()));
}
list.add(t);
}
return list;
}
}
测试类：
package com.xhh.Dao;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
import com.xhh.entity.Book;
import com.xhh.util.BaseDao;
import com.xhh.util.DBAccess;
import com.xhh.util.PageBean;
import com.xhh.util.StringUtils;
public class BookDao2 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);
}
//测试普通的查询
public static void main(String[] args) {
BookDao2 bookDao = new BookDao2();
Book book = new Book();
try {
book.setBname("圣墟");
List<Book> list = bookDao.list(book, null);
for (Book b : list) {
System.out.println(b);
}
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
运行结果：
通用分页查询：BaseDao2
package com.xhh.util;
import java.lang.reflect.Field;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
import com.xhh.entity.Book;
public class BaseDao2<T> {
/**
* @param sql 可能不同的表，那么意味着sql是变化的，那么它是从子类处理好在传递到父类
* @param clz 需要返回不同的对象集合 Book.class/Order.class
* @param pageBean 可能要分页
* @return
* @throws SQLException
* @throws IllegalAccessException
* @throws InstantiationException
*/
public List<T> executeQuery(String sql,Class clz,PageBean pageBean) throws SQLException, InstantiationException, IllegalAccessException{
List<T> list = new ArrayList<>();
Connection con = DBAccess.getConnection();
PreparedStatement pst = null;
ResultSet rs = null;
if(pageBean != null && pageBean.isPagination()) {
//分页
/**
* 1.分页是与分页助手类pagebean中的total有关，需要查询数据库得到total赋值给bean
* 2.查询出符合条件的某一页的数据
*/
String countsql = getCountsql(sql);
pst = con.prepareStatement(countsql);
rs = pst.executeQuery();
if(rs.next()){
pageBean.setTotal(rs.getObject(1).toString());
}
/**
* --分页的查询语句
select * from t_mvc_book where bname like '%斗破%' limit 起始下标,变量
*/
String pagesql = getPagesql(sql, pageBean);
pst = con.prepareStatement(pagesql);
rs = pst.executeQuery();
}else {
//不分页
pst = con.prepareStatement(sql);
rs = pst.executeQuery();
}
T t = null;
while (rs.next()) {
/**
* 1. 实例化一个你要查询的对象 （比如book）
* 2. 通过对象的属性名去游标中取出属性值（通过反射来完成）
* 2.1 获取到类对象中的属性
* 2.2 给属性赋值
* 3. 已经赋值好的实例对象放入到list集合当中
*/
t = (T) clz.newInstance();
Field [] fields = clz.getDeclaredFields();
for (Field f : fields) {
f.setAccessible(true);
f.set(t, rs.getObject(f.getName()));
}
list.add(t);
}
return list;
}
private String getPagesql(String sql , PageBean pageBean) {
return sql + " limit " +pageBean.getStartIndex()+","+pageBean.getRows();
}
private String getCountsql(String sql) {
return "select count(1) from ("+sql+") t";
}
}
测试类：
package com.xhh.Dao;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
import com.sun.scenario.effect.impl.sw.sse.SSEBlend_COLOR_BURNPeer;
import com.xhh.entity.Book;
import com.xhh.util.BaseDao;
import com.xhh.util.BaseDao2;
import com.xhh.util.DBAccess;
import com.xhh.util.PageBean;
import com.xhh.util.StringUtils;
public class BookDao3 extends BaseDao2<Book>{
public List<Book> list(Book book,PageBean pageBean) throws Exception{
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);
}
//测试
public static void main(String[] args) {
BookDao3 bookDao = new BookDao3();
Book book = new Book();
book.setBname("圣墟");
PageBean pageBean=new PageBean();
pageBean.setRows(10);
try {
List<Book> list = bookDao.list(book, pageBean);
for (Book b : list) {
System.out.println(b);
}
System.out.println(pageBean);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
运行结果：
分页的优势：
1.带来大量无目的流量
2.无阻断体验度提升
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