目录
前言:
封装的优点：
接下来看代码吧：
通用分页是对分页进行一个代码的封装，原有分页代码存在大量重复代码，这次的分享就是将其简化
能够达到简化分页代码相关功能的开发
相对应的包、类：
BaseDao:
package util; import java.sql.Connection; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.util.List; public class BaseDao{ // public List executeQuery(String sql,PageBean pageBean,CallBack callBack) throws Exception{ // // //创建连接 // Connection con = DBAccess.getConnection();// 重复代码1 // //获取执行对象 // PreparedStatement ps = con.prepareStatement(sql);// 重复代码2 // //获取结果集 // ResultSet rs = ps.executeQuery();// 重复代码3 // //循环遍历结果集 while(rs.next()) { list.add(new Book(rs.getInt("bid"), rs.getString("bname"), rs.getFloat("price"))); } // //查询不同的表，必然要处理不同的结果集 // //接口是调用方来实现 // return callBack.foreach(rs); // } public List executeQuery(String sql,PageBean pageBean,CallBack callBack) throws Exception{ // select * from tb_book where bname like '%o%'; //这个查询不行，因为跟上面代码查询组装不起来 // select count(*) from tb_book where bname like '%o%' //所以说为什么要这么变，因为不仅仅考虑写出来简单，你还要发现转变的问题 // String countsql="select count(1) as n from ("+sql+") t"; //但这个可以组装 //从上面得到select count(1) as n from (select * from tb_book where bname like '%o%') t; //目的是为了得到总记录数-->得到总页数 // select * from tb_book where bname like '%o%' limit 10,10; //创建连接 Connection con = null;// 重复代码1 //获取执行对象 PreparedStatement ps = null;// 重复代码2 //获取结果集 ResultSet rs = null;// 重复代码3 //判断是否分页 并且判断是否为true if(pageBean != null && pageBean.isPagination()) {//说明要分页 //拿到总记录数 拼接原始的mysql String countSQL = getcountSQL(sql); con = DBAccess.getConnection();// 重复代码1 ps = con.prepareStatement(countSQL);// 重复代码2 rs= ps.executeQuery();// 重复代码3 //查询出来的总行数是不是单行单列啊，所以说不需要while,判断即可 if(rs.next()) { //把我们查询出来的总记录数放在pageBean里面，pageBean它是包含了所有的分页的一些元素的实体类 //当前实体类就包含了总记录数 pageBean.setTotal(rs.getString("n")); } //拼接 String pageSQL = pagePageSQL(sql,pageBean); con = DBAccess.getConnection();// 重复代码1 ps = con.prepareStatement(pageSQL);// 重复代码2 rs= ps.executeQuery();// 重复代码3 } else { con = DBAccess.getConnection();// 重复代码1 ps = con.prepareStatement(sql);// 重复代码2 rs= ps.executeQuery();// 重复代码3 } return callBack.foreach(rs); } private String pagePageSQL(String sql, PageBean pageBean) { //这里相当于limit 1,10 return sql+" limit "+pageBean.getStartIndex()+","+pageBean.getRows(); } private String getcountSQL(String sql) { // select * from tb_book where bname like '%o%'; //这个查询不行，因为跟上面代码查询组装不起来 // select count(*) from tb_book where bname like '%o%' //所以说为什么要这么变，因为不仅仅考虑写出来简单，你还要发现转变的问题 // String countsql="select count(1) as n from ("+sql+") t"; //下面这行代码就解决了上面的问题，由原始SQL换成查询总行数的SQL //为什么不是*因为*代表的所以列，而写1代表的是一列，哪个性能更好，肯定是1 return "select count(1) as n from ("+sql+") t"; } }
CallBack：
package util; import java.sql.ResultSet; import java.util.List; public interface CallBack{ List foreach(ResultSet rs); }
DBAccess:
package 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;
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);
}
}
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() {
// 因为这个mysql8的驱动包
return "com.mysql.cj.jdbc.Driver".equals(driver);
}
public static void main(String[] args) {
Connection conn = DBAccess.getConnection();
System.out.println(conn);
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");
}
}
EncodingFiter:
package 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;
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();
}
}
}
PageBean:
package util;
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;
}
public int getStartIndex() {
return (this.page - 1) * this.rows;
}
@Override
public String toString() {
return "PageBean [page=" + page + ", rows=" + rows + ", total=" + total + ", pagination=" + pagination + "]";
}
}
StringUtils:
package 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() {
}
public static boolean isBlank(String s) {
boolean b = false;
if (null == s || s.trim().equals("")) {
b = true;
}
return b;
}
public static boolean isNotBlank(String s) {
return !isBlank(s);
}
}
config.properties:
#mysql driver=com.mysql.jdbc.Driver url=jdbc:mysql://localhost:3306/mybatis?useUnicode=true&characterEncoding=UTF-8&useSSL=false user=root pwd=123456
实体类：book
package 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() {
// TODO Auto-generated constructor stub
}
public Book(int bid, String bname, float price) {
super();
this.bid = bid;
this.bname = bname;
this.price = price;
}
}
BookDao：
package 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 util.BaseDao; import util.DBAccess; import util.PageBean; import util.StringUtils; import entity.Book; public class BookDao extends BaseDao{ //S阶段 public List list(Book book,PageBean pageBean) throws Exception{ List list = new ArrayList (); //创建连接 Connection con = DBAccess.getConnection();// 重复代码1 //定义sql语句 String sql = "select * from t_mvc_book where 1=1 "; //假如按照书籍的名字查询 String bname = book.getBname(); //如果说这个书籍不为空，你就是想让书籍查询 if(StringUtils.isNotBlank(bname)) { sql += " and bname like '%"+bname+"%'"; } //假设按照id进行查询 int bid = book.getBid(); //判断是否为空 if(bid != 0) { sql+=" and bid ="+bid; } //获取执行对象 PreparedStatement ps = con.prepareStatement(sql);// 重复代码2 //获取结果集 ResultSet rs = ps.executeQuery();// 重复代码3 //循环遍历结果集 while(rs.next()) { list.add(new Book(rs.getInt("bid"), rs.getString("bname"), rs.getFloat("price"))); } return list; } //Y阶段第1个版本 public List list2(Book book,PageBean pageBean) throws Exception{ //定义sql语句 String sql = "select * from t_mvc_book where 1=1 "; //假如按照书籍的名字查询 String bname = book.getBname(); //如果说这个书籍不为空，你就是想让书籍查询 if(StringUtils.isNotBlank(bname)) { sql += " and bname like '%"+bname+"%'"; } //假设按照id进行查询 int bid = book.getBid(); //判断是否为空 if(bid != 0) { sql+=" and bid ="+bid; } //调用的rs的方法返回的是list集合，所以说list集合，返回Book里面的值 return super.executeQuery(sql, pageBean, rs->{ List list = new ArrayList<>(); try { while(rs.next()) { list.add(new Book(rs.getInt("bid"), rs.getString("bname"), rs.getFloat("price"))); } } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } return list; }); } //增删改 public static void main(String[] args) throws Exception { List list = new BookDao().list(new Book(), null); for (Book book : list) { System.out.println(book); } } }
bookdaotest:
在bookdao里面进行下面的操作：
然后下面的方法就出来了，再进行一些方法的补充就行了：
package dao;
import static org.junit.Assert.*;
import java.util.List;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import entity.Book;
import util.PageBean;
public class BookDaoTest {
@Before
public void setUp() throws Exception {
System.out.println("被测试方法执行之前调用");
}
@After
public void tearDown() throws Exception {
System.out.println("被测试方法执行之后调用");
}
@Test
public void testList() throws Exception {
List list = new BookDao().list(new Book(), null);
for (Book book : list) {
System.out.println(book);
}
}
@Test
public void testList2() throws Exception {
List list = new BookDao().list2(new Book(), null);
for (Book book : list) {
System.out.println(book);
}
}
@Test
public void testList3() throws Exception {
Book b = new Book();
//如果说只想查询关于一个的o
b.setBname("o");
PageBean pageBean = new PageBean();
//如果想要查询第二的数据
pageBean.setPage(1);
//如果我一页不想显示10条想显示20
pageBean.setRows(20);
List list = new BookDao().list2(b, pageBean);
for (Book book : list) {
System.out.println(book);
}
}
}
结果：
好啦，今天的分享就到这，咱们下次再见！
