Java通用分页
1.什么是通用分页
通用分页是一种在Java Web开发中广泛使用的技术，它用于处理大量数据并将它们分成多个页面进行显示。通用分页通常包括一个分页组件和分页查询方法，该方法使用分页参数查询并返回指定页面和指定数量的数据结果。通常可以设置每页显示的数据数量，当前页面的页码以及总共的数据数量等。
通用分页的主要目的是为了更方便地浏览并处理大量数据。使用通用分页可以减轻服务器负担，提高数据处理效率和页面加载速度，同时也能使数据更加直观和易于管理。在开发中，通用分页通常会配合前端框架一起使用，以实现更好的用户体验。
2.反射完成通用的查询功能
编写一组获得或关闭数据库对象的方法：
package com.xiaoye.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.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");
}
}
编写一个能够连接数据库的方法：
编写一个私有的构造方法：
package com.xiaoye.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);
}
}
编写一个分页工具类：
package com.xiaoye.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 + "]";
}
}
编写一个过滤器（凡是被过滤器处理的都变成了 中文乱码处理）：
package com.xiaoye.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;
/**
* 过滤器
* 凡是被过滤器处理的都变成了 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();
}
}
}
编写实体类BOOK:
package com.xiaoye.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;
}
}
编写BookDao :
public List list1(Book book, PageBean bean) throws Exception {
List list = new ArrayList();
Connection conn = DBAccess.getConnection();
String sql = "select * from t_mvc_book where 1=1";
String bname = book.getBname();
// 判断bname不为空的情况下才进行
if (StringUtils.isNotBlank(bname)) {
sql += " and bname LIKE '%" + bname + "%'";
}
PreparedStatement ps = conn.prepareStatement(sql);
ResultSet rs = ps.executeQuery();
while (rs.next()) {
Book b = new Book();
b.setBid(rs.getInt("bid"));
b.setBname(rs.getString("bname"));
b.setPrice(rs.getFloat("price"));
l.add(b);
}
return l;
}
输出结果：
编写basedao：
代码重复：必须要写的
Connection conn = DBAccess.getConnection();
PreparedStatement ps = conn.prepareStatement(sql);
ResultSet rs = ps.executeQuery();流程重复：
创建表对应的实体类对象，将查询出来的结果集添加到实例化对象的属性中，已经被填充的实体对象，加入到集合中
Book b=new Book();
b.setBid(rs.getInt("bid"));
b.setBname(rs.getString("bname"));
b.setPrice(rs.getFloat("price"));
l.add(b); 创建一个basedao泛型basedao
package com.xiaoye.util;
import java.lang.reflect.Field;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;
import com.xiaoye.entity.Book;
public class BaseDao {
public List executeQuery(String sql,Class clz,PageBean p) throws Exception{
List list = new ArrayList();
Connection conn = DBAccess.getConnection();
PreparedStatement ps = conn.prepareStatement(sql);
ResultSet rs = ps.executeQuery();
while(rs.next()) {
T t = (T) clz.newInstance();
//拿到clz对应的所有属性对象
Field[] fields = clz.getDeclaredFields();
for (Field f : fields) {
f.setAccessible(true);//打开访问权限
f.set(t, rs.getObject(f.getName()));
}
list.add(t);
}
return list;
}
} 到BOOKDAO进行代码测试：
public List list2(Book book,PageBean pegeBean) throws Exception{
String sql ="select * from t_mvc_book where 1=1";
String bname = book.getBname();
if(StringUtils.isNotBlank(bname)) {
sql +=" and bname like '%"+bname+"%'";
}
return super.exrcuteQuery(sql, Book.class, pegeBean);
}
使用main方法测试：
public static void main(String[] args) throws Exception {
BookDao bookDao=new BookDao();
Book book=new Book();
book.setBname("圣墟");
PageBean pageBen=new PageBean();
List list = bookDao.list(book, pageBen);
for (Book b : list) {
System.out.println(b);
}
} 输出结果：
4.junit单元测试：
JUnit是一个Java语言的单元测试框架，用于编写和运行自动化测试，JUnit提供了测试框架，用于测试Java代码的各种方面，包括方法的返回值和异常处理
在bookDao里面建立两个test：
@Test
public void test() throws Exception {
System.out.println("test1..");
BookDao bookDao=new BookDao();
Book book=new Book();
book.setBname("圣墟");
PageBean pageBen=new PageBean();
List list = bookDao.list1(book, pageBen);
for (Book b : list) {
System.out.println(b);
}
}
@Test
public void test2() throws Exception {
System.out.println("test2..");
BookDao bookDao=new BookDao();
Book book=new Book();
book.setBname("圣墟");
PageBean pageBen=new PageBean();
List list = bookDao.list2(book, pageBen);
for (Book b : list) {
System.out.println(b);
}
} 输出结果：
5.通用查询带分页：
在BaseDAO里面写两个方法：pegeBean sql
package com.xiaoye.util;
import java.lang.reflect.Field;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;
import com.xiaoye.entity.Book;
public class BaseDao {
/**
*
* @param sql
* @param c Book.class
* @param pegeBean
* @return
* @throws Exception
*/
public List exrcuteQuery(String sql,Class c,PageBean pegeBean) throws Exception{
List l=new ArrayList();
Connection con = null;
PreparedStatement ps = null;
ResultSet rs = null;
if(pegeBean !=null && pegeBean.isPagination()) {
String countSQL=getCountSQL(sql);
con=DBAccess.getConnection();
ps = con.prepareStatement(countSQL);
rs = ps.executeQuery();
if(rs.next()) {
pegeBean.setTotal(rs.getObject("n").toString());
}
String pageSQL=getPageSQL(sql,pegeBean);
con=DBAccess.getConnection();
ps = con.prepareStatement(pageSQL);
rs = ps.executeQuery();
}else {
con=DBAccess.getConnection();
ps = con.prepareStatement(sql);
rs = ps.executeQuery();
}
while(rs.next()) {
T t=(T) c.newInstance();
//拿到class对应的使用对象
Field[] fields = c.getDeclaredFields();
for (Field f : fields) {
f.setAccessible(true);
// System.out.println(f.getName());
f.set(t, rs.getObject(f.getName()));
}
l.add(t);
}
return l;
}
/**
* 拼接出最终展示出的数据sql
* @param sql 原生sql
* @param pegeBean
* @return
*/
private String getPageSQL(String sql, PageBean pegeBean) {
return sql+" limit "+pegeBean.getStartIndex()+","+pegeBean.getRows();
}
/**
* 拼接出查询符合条件的总记录sql
* @param sql
* @return
*/
private String getCountSQL(String sql) {
return "SELECT count(1) as n from ("+sql+") t";
}
}
然后在BookDao里面在写一个Test：
@Test
public void test3() throws Exception {
System.out.println("test3..");
BookDao bookDao=new BookDao();
Book book=new Book();
book.setBname("圣墟");
PageBean pageBen=new PageBean();
//不需要分页
// pageBen.setPagination(false);
//查询第二页的数据
// pageBen.setPage(2);
List list = bookDao.list2(book, pageBen);
for (Book b : list) {
System.out.println(b);
}
System.out.println(pageBen);
} 输出结果：
不需要分页：
pageBen.setPagination(false);输出结果：
查询第二页的数据：
pageBen.setPage(2);输出结果：
没有用以上两种方法：
@Test
public void test3() throws Exception {
System.out.println("test3..");
BookDao bookDao=new BookDao();
Book book=new Book();
book.setBname("圣墟");
PageBean pageBen=new PageBean();
//不需要分页
// pageBen.setPagination(false);
//查询第二页的数据
// pageBen.setPage(2);
List list = bookDao.list2(book, pageBen);
for (Book b : list) {
System.out.println(b);
}
System.out.println(pageBen);
} 输出结果：
动起来你们的双手
