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:

Java通用分页_第1张图片

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:

Java通用分页_第2张图片

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:

Java通用分页_第3张图片

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:

Java通用分页_第4张图片

 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:

Java通用分页_第5张图片 

 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: 

Java通用分页_第6张图片

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:

Java通用分页_第7张图片 动起来你们的双手

 Java通用分页_第8张图片

 

 

 

 

 

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