java的分页原理详解

首先先创建一个Student实体类。

import java.io.Serializable;
import java.util.Map;

public class Student implements Serializable {
    //实现序列化接口，用于对象的持久化
    private static final long serialVersionUID = -7476381137287496245L;
    //学生记录id
    private int id;
    //学生姓名
    private String stuName;
    //学生年龄
    private int age;
    //学生性别
    private int gender;
    //学生住址
    private String address;
    //空构造器
    public Student() {
        super();
    }
/**
 * 构造器
 * @param id  学生记录id
 * @param stuName 学生姓名
 * @param age 学生年龄
 * @param gender 学生性别
 * @param address 学生住址
 */
    public Student(int id, String stuName, int age, int gender, String address) {
        super();
        this.id = id;
        this.stuName = stuName;
        this.age = age;
        this.gender = gender;
        this.address = address;
    }
/**
 *     该构造器用于将Map中的数据封装到Student类中，
 *  在构造器中传入Map参数。
 * @param map
 */
    public Student(Map<String, Object> map){
        this.id = (Integer)map.get("id");
        this.stuName = (String)map.get("stu_name");
        this.age = (Integer)map.get("age");
        this.gender = (Integer)map.get("gender");
        this.address = (String)map.get("address");
    }
    /*
     * Getter Setter方法
     */
    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getStuName() {
        return stuName;
    }

    public void setStuName(String stuName) {
        this.stuName = stuName;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public int getGender() {
        return gender;
    }

    public void setGender(int gender) {
        this.gender = gender;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }
/*
 * 重写toString方法
 * @see java.lang.Object#toString()
 */
    @Override
    public String toString() {
        return "Student [id=" + id + ", stuName=" + stuName + ", age=" + age
                + ", gender=" + gender + ", address=" + address + "]";
    }

}

创建Pager类

import java.io.Serializable;
import java.util.List;

public class Pager<T> implements Serializable {
    //实现序列化接口用于对象持久化
    private static final long serialVersionUID = -8741766802354222579L;
     // 每页显示多少条记录
    private int pageSize;
    //当前第几页数据
    private int currentPage;
    // 一共多少条记录
    private int totalRecord;
    // 一共多少页记录
    private int totalPage;
    //要显示的数据
    private List<T> dataList;
    //构造函数
    public Pager(int pageNum, int pageSize, List<T> sourceList){
        //如果数据源为空 跳出该构造方法
        if(sourceList == null || sourceList.isEmpty()){
            return;
        }

        // 总记录条数等于数据源的长度
        this.totalRecord = sourceList.size();

        // 每页显示多少条记录
        this.pageSize = pageSize;

        //获取最大页数  所有记录除以每页显示的条数
        this.totalPage = this.totalRecord / this.pageSize;
        if(this.totalRecord % this.pageSize !=0){
            this.totalPage = this.totalPage + 1;
        }

        // 当前第几页数据  如果参数pageNum超过最大页数
        this.currentPage = this.totalPage < pageNum ?  this.totalPage : pageNum;

        // 起始索引
        int fromIndex    = this.pageSize * (this.currentPage -1);

        // 结束索引
        int toIndex  = this.pageSize * this.currentPage > this.totalRecord ? this.totalRecord : this.pageSize * this.currentPage;

        this.dataList = sourceList.subList(fromIndex, toIndex);
    }
    //空构造器
    public Pager(){

    }
    //构造器
    public Pager(int pageSize, int currentPage, int totalRecord, int totalPage,
            List<T> dataList) {
        super();
        this.pageSize = pageSize;
        this.currentPage = currentPage;
        this.totalRecord = totalRecord;
        this.totalPage = totalPage;
        this.dataList = dataList;
    }
    /*
     * Getter 和  Setter 方法
     */
    public int getPageSize() {
        return pageSize;
    }

    public void setPageSize(int pageSize) {
        this.pageSize = pageSize;
    }

    public int getCurrentPage() {
        return currentPage;
    }

    public void setCurrentPage(int currentPage) {
        this.currentPage = currentPage;
    }

    public int getTotalRecord() {
        return totalRecord;
    }

    public void setTotalRecord(int totalRecord) {
        this.totalRecord = totalRecord;
    }

    public int getTotalPage() {
        return totalPage;
    }

    public void setTotalPage(int totalPage) {
        this.totalPage = totalPage;
    }

    public List<T> getDataList() {
        return dataList;
    }

    public void setDataList(List<T> dataList) {
        this.dataList = dataList;
    }

}

创建一个常量Constant类

public class Constant {

    /**
     * 男性
     */
    public static final int GENDER_MALE = 1;

    /**
     * 女性
     */
    public static final int GENDER_FEMALE = 2;

    /**
     * 默认每页显示多少条记录
     */
    public static final int DEFAULT_PAGE_SIZE = 5;

    /**
     * 默认显示第几页记录
     */
    public static final int DEFAULT_PAGE_NUM = 1;

    /**
     * 默认学生性别
     */
    public static final int DEFAULT_GENDER = 0;
}

创建StudentDAO类

public interface StudentDao {

    /**
     * 根据查询条件，查询学生分页信息
     *
     * @param searchModel
     *            封装查询条件
     * @param pageNum
     *            查询第几页数据
     * @param pageSize
     *            每页显示多少条记录
     * @return 查询结果
     */
    public Pager<Student> findStudent(Student searchModel, int pageNum,
            int pageSize);
}

创建一个JdbcUtil工具类

public class JdbcUtil {

    // 表示定义数据库的用户名
    private static String USERNAME ;

    // 定义数据库的密码
    private static String PASSWORD;

    // 定义数据库的驱动信息
    private static String DRIVER;

    // 定义访问数据库的地址
    private static String URL;

    // 定义数据库的链接
    private Connection connection;

    // 定义sql语句的执行对象
    private PreparedStatement pstmt;

    // 定义查询返回的结果集合
    private ResultSet resultSet;

    static{
        //加载数据库配置信息，并给相关的属性赋值
        loadConfig();
    }

    /**
     * 加载数据库配置信息，并给相关的属性赋值
     * 从项目的jdbc.properties文件读取信息
     * 然后设置连接参数
     */
    public static void loadConfig() {
        try {
            InputStream inStream = JdbcUtil.class
                    .getResourceAsStream("/jdbc.properties");
            Properties prop = new Properties();
            prop.load(inStream);
            USERNAME = prop.getProperty("jdbc.username");
            PASSWORD = prop.getProperty("jdbc.password");
            DRIVER= prop.getProperty("jdbc.driver");
            URL = prop.getProperty("jdbc.url");
        } catch (Exception e) {
            throw new RuntimeException("读取数据库配置文件异常！", e);
        }
    }

    public JdbcUtil() {

    }

    /**
     * 获取数据库连接
     *
     * @return 数据库连接
     */
    public Connection getConnection() {
        try {
            Class.forName(DRIVER); // 注册驱动
            connection = DriverManager.getConnection(URL, USERNAME, PASSWORD); // 获取连接
        } catch (Exception e) {
            throw new RuntimeException("get connection error!", e);
        }
        return connection;
    }

    /**
     * 执行更新操作
     *
     * @param sql
     *            sql语句
     * @param params
     *            执行参数
     * @return 执行结果
     * @throws SQLException
     */
    public boolean updateByPreparedStatement(String sql, List<?> params)
            throws SQLException {
        boolean flag = false;
        int result = -1;// 表示当用户执行添加删除和修改的时候所影响数据库的行数
        pstmt = connection.prepareStatement(sql);
        int index = 1;
        // 填充sql语句中的占位符  依次填入预处理语句所需的参数
        if (params != null && !params.isEmpty()) {
            for (int i = 0; i < params.size(); i++) {
                pstmt.setObject(index++, params.get(i));
            }
        }
        result = pstmt.executeUpdate();
        flag = result > 0 ? true : false;
        return flag;
    }

    /**
     * 执行查询操作
     *
     * @param sql
     *            sql语句
     * @param params
     *            执行参数
     * @return
     * @throws SQLException
     */
    public List<Map<String, Object>> findResult(String sql, List<?> params)
            throws SQLException {
        //创建泛型为Map类型的List
        List<Map<String, Object>> list = new ArrayList<Map<String, Object>>();
        //预处理语句参数索引
        int index = 1;
        pstmt = connection.prepareStatement(sql);
        //依次填入参数
        if (params != null && !params.isEmpty()) {
            for (int i = 0; i < params.size(); i++) {
                pstmt.setObject(index++, params.get(i));
            }
        }
        //执行预处理语句 获得结果集
        resultSet = pstmt.executeQuery();
        //获取源数据
        ResultSetMetaData metaData = resultSet.getMetaData();
        //获取源数据的条数
        int cols_len = metaData.getColumnCount();
        //遍历resultSet将数据放入map中   再将map放入list中
        while (resultSet.next()) {
            Map<String, Object> map = new HashMap<String, Object>();
            for (int i = 0; i < cols_len; i++) {
                String cols_name = metaData.getColumnName(i + 1);
                Object cols_value = resultSet.getObject(cols_name);
                if (cols_value == null) {
                    cols_value = "";
                }
                map.put(cols_name, cols_value);
            }
            list.add(map);
        }
        return list;
    }

    /**
     * 释放资源
     */
    public void releaseConn() {
        if (resultSet != null) {
            try {
                resultSet.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if (pstmt != null) {
            try {
                pstmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if (connection != null) {
            try {
                connection.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

}

创建JdbcSqlStudentDaoImpl类

/**
 * 使用mysql数据库limit关键字实现分页
 *
 *
 *
 */
public class JdbcSqlStudentDaoImpl implements StudentDao {
    //实现查询的方法
    @Override
    public Pager<Student> findStudent(Student searchModel, int pageNum,
            int pageSize) {
        //存放获取的数据
        Pager<Student> result = null;
        // 存放查询参数
        List<Object> paramList = new ArrayList<Object>();
        //获取查询参数Name
        String stuName = searchModel.getStuName();
        //获取查询参数gender
        int gender = searchModel.getGender();
        //创建查询语句
        StringBuilder sql = new StringBuilder(
                "select * from t_student where 1=1");
        //得到所有的记录条数
        StringBuilder countSql = new StringBuilder(
                "select count(id) as totalRecord from t_student where 1=1 ");
        //如果stuName存在且不为空的话 在两条sql语句后面加上查询条件
        if (stuName != null && !stuName.equals("")) {
            sql.append(" and stu_name like ?");
            countSql.append(" and stu_name like ?");
            //查询条件放入 查询参数集合中
            paramList.add("%" + stuName + "%");
        }
        //如果gender的值 等于两个常量中的其中一个时
        if (gender == Constant.GENDER_FEMALE || gender == Constant.GENDER_MALE) {
            sql.append(" and gender = ?");
            countSql.append(" and gender = ?");
            paramList.add(gender);
        }

        // 起始索引
        int fromIndex    = pageSize * (pageNum -1);

        // 使用limit关键字，实现分页
        sql.append(" limit " + fromIndex + ", " + pageSize );

        // 存放所有查询出的学生对象
        List<Student> studentList = new ArrayList<Student>();
        //创建JDBC工具类
        JdbcUtil jdbcUtil = null;
        try {
            jdbcUtil = new JdbcUtil();
            // 获取数据库链接
            jdbcUtil.getConnection(); 

            // 获取总记录数
            List<Map<String, Object>> countResult = jdbcUtil.findResult(countSql.toString(), paramList);
            //获取List中的第一个Map
            Map<String, Object> countMap = countResult.get(0);
            //获取Map中的键值为totalRecord的值
            int totalRecord = ((Number)countMap.get("totalRecord")).intValue();

            // 获取查询的学生记录
            List<Map<String, Object>> studentResult = jdbcUtil.findResult(sql.toString(), paramList);
            //将Map中的数据遍历出来封装成student类 再放入studentlist中去
            if (studentResult != null) {
                for (Map<String, Object> map : studentResult) {
                    Student s = new Student(map);
                    studentList.add(s);
                }
            }

            //获取总页数
            int totalPage = totalRecord / pageSize;
            if(totalRecord % pageSize !=0){
                totalPage++;
            }

            // 组装pager对象
            result = new Pager<Student>(pageSize, pageNum,
                            totalRecord, totalPage, studentList);

        } catch (SQLException e) {
            throw new RuntimeException("查询所有数据异常！", e);
        } finally {
            if (jdbcUtil != null) {
                jdbcUtil.releaseConn(); // 一定要释放资源
            }
        }
        return result;
    }

}

创建service类

public interface StudentService {

    /**
     * 根据查询条件，查询学生分页信息
     *
     * @param searchModel
     *            封装查询条件
     * @param pageNum
     *            查询第几页数据
     * @param pageSize
     *            每页显示多少条记录
     * @return 查询结果
     */
    public Pager<Student> findStudent(Student searchModel, int pageNum,
            int pageSize);
}

创建Servlet类

public class JdbcSqlServlet extends HttpServlet {

    private static final long serialVersionUID = -318134993070614515L;

    private StudentService studentService = new JdbcSqlStudentServiceImpl();

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        doPost(request, response);
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // 接收request里的参数
        String stuName = request.getParameter("stuName"); //学生姓名

        // 获取学生性别
        //如果没有获取到就赋值为默认数值
        int gender = Constant.DEFAULT_GENDER;
        String genderStr = request.getParameter("gender");
        //如果符合条件就转化为Int类型
        if(genderStr!=null && !"".equals(genderStr.trim())){
            gender = Integer.parseInt(genderStr);
        }

        // 校验pageNum参数输入合法性
        String pageNumStr = request.getParameter("pageNum");
        //如果页码数不是数字的话
        if(pageNumStr !=null && !StringUtil.isNum(pageNumStr)){
            request.setAttribute("errorMsg", "参数传输错误");
            request.getRequestDispatcher("jdbcSqlStudent.jsp").forward(request, response);
            return;
        }
         //显示第几页数据
        int pageNum = Constant.DEFAULT_PAGE_NUM;
        //获取页码数
        if(pageNumStr!=null && !"".equals(pageNumStr.trim())){
            pageNum = Integer.parseInt(pageNumStr);
        }

        int pageSize = Constant.DEFAULT_PAGE_SIZE;  // 每页显示多少条记录
        String pageSizeStr = request.getParameter("pageSize");
        if(pageSizeStr!=null && !"".equals(pageSizeStr.trim())){
            pageSize = Integer.parseInt(pageSizeStr);
        }

        // 组装查询条件
        Student searchModel = new Student();
        searchModel.setStuName(stuName);
        searchModel.setGender(gender);

        //调用service 获取查询结果
        Pager<Student> result = studentService.findStudent(searchModel,
                                                                pageNum, pageSize);

        // 返回结果到页面
        request.setAttribute("result", result);
        request.setAttribute("stuName", stuName);
        request.setAttribute("gender", gender);

        request.getRequestDispatcher("jdbcSqlStudent.jsp").forward(request, response);
    }

}

加上一个正则工具类用于判断输入的参数是否为数字

public class StringUtil {

    /**
     * 校验字符串是否是大于0的数字
     * @param string
     * @return
     */
    public static boolean isNum(String string){
        Pattern pattern = Pattern.compile("[1-9]{1}\\d*");
        Matcher matcher = pattern.matcher(string);
        return matcher.matches();
    }
}