Author：相忠良
Email: ugoood@163.com
起始于：June 7, 2018
最后更新日期：June 8, 2018
声明：本笔记依据传智播客方立勋老师 Java Web 的授课视频内容记录而成，中间加入了自己的理解。本笔记目的是强化自己学习所用。若有疏漏或不当之处，请在评论区指出。谢谢。
涉及的图片，文档写完后，一次性更新。
本节案例是承接 day14 的客户关系管理系统，继续改造。
1. 分页实现(重点)
所需小知识，如下：
select id,name from customer limit 0,5;显示第1-5条数据，第1页；
select id,name from customer limit 5,5;显示第6-10条数据，第2页；
select id,name from customer limit 10,5;显示第11-15条数据，第3页。
分页结构图如下(重要的就是这个图，后面的工作均围绕这个图展开)：
上图涉及了3个封装数据的 javabean，先实现了他们！如下：
cn.wk.domain.PageBean：
package cn.wk.domain;
import java.util.List;
public class PageBean {
private List list;
private int totalrecord;
private int pagesize;
private int totalpage;
private int currentpage;
private int previouspage;
private int nextpage;
private int[] pagebar;
public int getPagesize() {
return pagesize;
}
public void setPagesize(int pagesize) {
this.pagesize = pagesize;
}
public List getList() {
return list;
}
public void setList(List list) {
this.list = list;
}
public int getTotalrecord() {
return totalrecord;
}
public void setTotalrecord(int totalrecord) {
this.totalrecord = totalrecord;
}
public int getTotalpage() {
if (this.totalrecord % this.pagesize == 0)
this.totalpage = this.totalrecord / this.pagesize;
else
this.totalpage = this.totalrecord / this.pagesize + 1;
return totalpage;
}
public int getCurrentpage() {
return currentpage;
}
public void setCurrentpage(int currentpage) {
this.currentpage = currentpage;
}
public int getPreviouspage() {
if (this.currentpage - 1 < 1)
this.previouspage = 1;
else
this.previouspage = this.currentpage - 1;
return previouspage;
}
public int getNextpage() {
if (this.currentpage + 1 >= this.totalpage)
this.nextpage = this.totalpage;
else
this.nextpage = this.currentpage + 1;
return nextpage;
}
public int[] getPagebar() {
int startpage;
int endpage;
int pagebar[] = null;
if (this.totalpage <= 10) {
pagebar = new int[this.totalpage];
startpage = 1;
endpage = this.totalpage;
} else {
pagebar = new int[10];
startpage = this.currentpage - 4;
endpage = this.currentpage + 5;
if (startpage < 1) {
startpage = 1;
endpage = 10;
}
if (endpage > this.totalpage) {
endpage = this.totalpage;
startpage = this.totalpage - 9;
}
}
int index = 0;
for (int i = startpage; i <= endpage; i++) {
pagebar[index++] = i;
}
this.pagebar = pagebar;
return this.pagebar;
}
}
cn.wk.domain.QueryInfo：
package cn.wk.domain;
public class QueryInfo {
private int currentpage = 1; // 用户要看的页
private int pagesize = 5; // 用户想看的页面大小
private int startindex; // 记住用户看的页的数据在数据库的起始位置
public int getCurrentpage() {return currentpage;}
public void setCurrentpage(int currentpage) {
this.currentpage = currentpage;
}
public int getPagesize() {return pagesize;}
public void setPagesize(int pagesize) {this.pagesize = pagesize;}
public int getStartindex() {
this.startindex = (this.currentpage - 1) * this.pagesize;
return startindex;
}
}
cn.wk.domain.QueryResult：
package cn.wk.domain;
import java.util.List;
public class QueryResult {
private List list; // 记住用户看的页的数据
private int totalrecord; // 记住总记录数
public List getList() {return list;}
public void setList(List list) {this.list = list;}
public int getTotalrecord() {return totalrecord;}
public void setTotalrecord(int totalrecord) {
this.totalrecord = totalrecord;
}
}
cn.wk.dao.impl.CustomerDaoImpl添加1个方法(同时将该方法声明加入cn.wk.dao.CustomerDao接口中)，如下：
/* 为分页功能 所添加的代码 */
// 获取页面数据和总记录数
public QueryResult pageQuery(int startindex, int pagesize) {
Connection conn = null;
PreparedStatement st = null;
ResultSet rs = null;
QueryResult qr = new QueryResult();
try {
conn = JdbcUtils.getConnection();
String sql = "select * from customer limit ?,?";
st = conn.prepareStatement(sql);
st.setInt(1, startindex);
st.setInt(2, pagesize);
rs = st.executeQuery();
List list = new ArrayList();
while (rs.next()) {
Customer c = new Customer();
c.setBirthday(rs.getDate("birthday"));
c.setCellphone(rs.getString("cellphone"));
c.setDescription(rs.getString("description"));
c.setEmail(rs.getString("email"));
c.setGender(rs.getString("gender"));
c.setId(rs.getString("id"));
c.setName(rs.getString("name"));
c.setPreference(rs.getString("preference"));
c.setType(rs.getString("type"));
list.add(c);
}
qr.setList(list);
// 总记录数
sql = "select count(*) from customer";
st = conn.prepareStatement(sql);
rs = st.executeQuery();
if (rs.next()) {
qr.setTotalrecord(rs.getInt(1));
}
return qr;
} catch (Exception e) {
throw new DaoException(e);
} finally {
JdbcUtils.release(conn, st, rs);
}
}
修改cn.wk.service.impl.BusinessServiceImpl，向其添加下面的方法(同时将该方法声明加入cn.wk.service.BusinessService接口中)，如下：
public PageBean pageQuery(QueryInfo queryInfo) {
// 调用 dao 获取页面数据
QueryResult qr = dao.pageQuery(queryInfo.getStartindex(),
queryInfo.getPagesize());
// 根据 dao 查询结果，生成页面显示所需的 pagebean
PageBean bean = new PageBean();
bean.setCurrentpage(queryInfo.getCurrentpage());
bean.setList(qr.getList());
bean.setPagesize(queryInfo.getPagesize());
bean.setTotalrecord(qr.getTotalrecord());
return bean;
}
修改cn.wk.web.controller.ListCustomerServlet如下：
package cn.wk.web.controller;
import java.io.IOException;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import cn.wk.domain.PageBean;
import cn.wk.domain.QueryInfo;
import cn.wk.service.BusinessService;
import cn.wk.service.impl.BusinessServiceImpl;
import cn.wk.utils.WebUtils;
// 用分页技术，得到所有客户显示
public class ListCustomerServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
try {
// 把 request 信息封装成 查询信息 bean 中
QueryInfo info = WebUtils.request2Bean(req, QueryInfo.class);
BusinessService service = new BusinessServiceImpl();
PageBean pagebean = service.pageQuery(info);
req.setAttribute("pagebean", pagebean);
req.getRequestDispatcher("/WEB-INF/jsp/listcustomer.jsp").forward(
req, resp);
} catch (Exception e) {
e.printStackTrace();
req.setAttribute("message", "查看客户失败！！");
req.getRequestDispatcher("/message.jsp").forward(req, resp);
}
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
doGet(req, resp);
}
}
最后，修改/WEB-INF/jsp/listcustomer.jsp(改成分页显示，而不是全部显示)如下：
<%@ taglib uri="/wk" prefix="wk"%>在 1.1 节有定义。
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<%@ taglib uri="/wk" prefix="wk"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<title>列出所有客户</title>
<style type="text/css">
.even{background-color:#FFFFCC}
.odd{background-color:#CCFFFF}
tr:hover{background-color:#FFCCCC}
</style>
</head>
<body style="text-align: center;">
<table frame="border" width="85%">
<tr>
<td>客户姓名</td>
<td>性别</td>
<td>生日</td>
<td>手机</td>
<td>邮箱</td>
<td>爱好</td>
<td>类型</td>
<td>备注</td>
<td>操作</td>
</tr>
<c:forEach var="c" items="#{requestScope.pagebean.list}" varStatus="status">
<tr class="${status.count%2==0?'even':'odd'}">
<td>${c.name }</td>
<td>${c.gender }</td>
<td>${c.birthday }</td>
<td>${c.cellphone }</td>
<td>${c.email }</td>
<td>${wk:sub(c.preference) }</td>
<td>${c.type }</td>
<td>${wk:sub(c.description) }</td>
<td>
<a href="${pageContext.request.contextPath}/servlet/EditCustomerServlet?id=${c.id}">修改</a>
<a href="javascript:void(0)" onclick="del(${c.id})">删除</a>
<!-- <a href="javascript:void(0)" onclick="del('${c.id}')">删除</a> 加单引号才能删，怕数据被别人删，所以注释掉 -->
</td>
</tr>
</c:forEach>
</table>
<br />
<script type="text/javascript">
function del(id){
if(window.confirm("您确定删除？？")){
window.location.href='${pageContext.request.contextPath}/servlet/DelCustomerServlet?id=' + id;
}
}
function gotopage(currentpage) {
if (currentpage < 1 || currentpage != parseInt(currentpage)
|| currentpage > ${pagebean.totalpage}) {
alert("请输入有效值！！");
document.getElementById("pagenum").value = '';
} else {
var pagesize = document.getElementById("pagesize").value;
window.location.href = '${pageContext.request.contextPath}/servlet/ListCustomerServlet?currentpage='
+ currentpage + '&pagesize=' + pagesize;
}
}
</script>
共[${pagebean.totalrecord}]条记录，
每页
<input type="text" id="pagesize" value="${pagebean.pagesize}"
onchange="gotopage(${pagebean.currentpage})" style="30px"
maxlength="2">条，
共[${pagebean.totalpage}]页，
当前第[${pagebean.currentpage}]页
<a href="javascript:void(0)"
onclick="gotopage(${pagebean.previouspage})">上一页</a>
<c:forEach var="pagenum" items="${pagebean.pagebar}">
<c:if test="${pagenum==pagebean.currentpage }">
<font color="red">${pagenum}</font>
</c:if>
<c:if test="${pagenum!=pagebean.currentpage }">
<a href="javascript:void(0)" onclick="gotopage(${pagenum})">${pagenum}</a>
</c:if>
</c:forEach>
<a href="javascript:void(0)" onclick="gotopage(${pagebean.nextpage})">下一页</a>
<input type="text" id="pagenum" style="35px" >
<input type="button" value=" GO " onclick="gotopage(document.getElementById('pagenum').value)">
</body>
</html>
1.1 自建 EL 表达式去处理简介过长问题
cn.wk.utils.MyEL，注意 EL 需建立静态方法，代码如下：
package cn.wk.utils;
public class MyEL {
public static String sub(String str) {
if (str.length() > 10)
return str.substring(0, 10) + "......";
return str;
}
}
再写一个tld文件，WEB-INFwk.tld：
<?xml version="1.0" encoding="UTF-8" ?>
<taglib xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd"
version="2.0">
<description>JSTL 1.1 functions library</description>
<display-name>JSTL functions</display-name>
<tlib-version>1.1</tlib-version>
<short-name>fn</short-name>
<uri>/wk</uri>
<function>
<name>sub</name>
<function-class>cn.wk.utils.MyEL</function-class>
<function-signature>java.lang.String sub(java.lang.String)</function-signature>
</function>
</taglib>
2. 完成客户关系管理案例
修改客户信息的cn.wk.web.controller.EditCustomerServlet：
package cn.wk.web.controller;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import cn.wk.domain.Customer;
import cn.wk.service.BusinessService;
import cn.wk.service.impl.BusinessServiceImpl;
import cn.wk.utils.Globals;
import cn.wk.utils.WebUtils;
public class EditCustomerServlet extends HttpServlet {
// 根据id获取要修改的客户信息
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
String id = req.getParameter("id");
BusinessService service = new BusinessServiceImpl();
Customer c = service.findCustomer(id);
req.setAttribute("genders", Globals.genders);
req.setAttribute("preferences", Globals.preferences);
req.setAttribute("types", Globals.types);
req.setAttribute("c", c);
req.getRequestDispatcher("/WEB-INF/jsp/editcustomer.jsp").forward(req,
resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
req.setCharacterEncoding("UTF-8");
// 把填写的表单修改信息封装到 customer 对象中
try {
Customer c = WebUtils.request2Bean(req, Customer.class); // 里面有id
BusinessService service = new BusinessServiceImpl();
service.updateCustomer(c);
req.setAttribute("message", "更新成功！！");
} catch (Exception e) {
e.printStackTrace();
req.setAttribute("message", "更新失败！！");
}
req.getRequestDispatcher("/message.jsp").forward(req, resp);
}
}
/WEB-INF/jsp/editcustomer.jsp如下(涉及数据回显)：
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/functions" prefix="fn" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>修改用户的视图</title>
<script type="text/javascript" src="${pageContext.request.contextPath }/js/ShowCalendar.js"></script>
<script type="text/javascript">
function makepre(){
var pres = document.getElementsByName("pre");
var preference = "";
for(var i = 0; i < pres.length; i++){
var input = pres[i];
if(input.checked==true){
preference = preference + input.value + ",";
}
}
// 组装字符串 跳舞,打麻将,看凤姐
preference = preference.substr(0, preference.length - 1);
var form = document.getElementById("form");
var input = document.createElement("input");
input.type = "hidden";
input.name = "preference";
input.value = preference;
form.appendChild(input);
return true;
}
</script>
</head>
<body style="text-align:center;">
<br />
<form id="form"
action="${pageContext.request.contextPath}/servlet/EditCustomerServlet"
method="post" onsubmit="return makepre()">
<!-- js代码，当按submit按钮时，就调用makepre()方法 -->
<table border="1" width="30%">
<input type="hidden" name="id" value="${c.id}">
<tr>
<td>客户姓名</td>
<td><input type="text" name="name" value="${c.name}"></td>
</tr>
<tr>
<td>性别</td>
<td><c:forEach var="gender" items="${genders}">
<input type="radio" name="gender" value="${gender}" ${c.gender==gender?'checked':'' }> ${gender}
</c:forEach></td>
</tr>
<tr>
<td>生日</td>
<td><input type="text" name="birthday"
onClick="showCalendar(this.id)" id="birthday" value="${c.birthday}"></td>
</tr>
<tr>
<td>手机</td>
<td><input type="text" name="cellphone" value="${c.cellphone}"></td>
</tr>
<tr>
<td>邮箱</td>
<td><input type="text" name="email" value="${c.email}"></td>
</tr>
<tr>
<td>爱好</td>
<td><c:forEach var="p" items="${preferences}">
<input type="checkbox" name="pre" value="${p}" ${fn:contains(c.preference,p)?'checked':'' }>${p}
</c:forEach></td>
</tr>
<tr>
<td>客户类型</td>
<td><c:forEach var="t" items="${types}">
<input type="radio" name="type" value="${t}" ${c.type==t?'checked':''}>${t}
</c:forEach></td>
</tr>
<tr>
<td>客户备注</td>
<td>
<textarea rows="5" cols="100" name="description">${c.description}</textarea>
</td>
</tr>
<tr>
<td><input type="reset" value="重置"></td>
<td><input type="submit" value="修改客户"></td>
</tr>
</table>
</form>
</body>
</html>
删除客户数据的cn.wk.web.controller.DelCustomerServlet：
package cn.wk.web.controller;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import cn.wk.service.BusinessService;
import cn.wk.service.impl.BusinessServiceImpl;
// 删除记录
public class DelCustomerServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
try {
String id = req.getParameter("id");
BusinessService service = new BusinessServiceImpl();
service.deleteCustomer(id);
req.setAttribute("message", "删除成功！！");
} catch (Exception e) {
e.printStackTrace();
req.setAttribute("message", "删除失败！！");
}
req.getRequestDispatcher("/message.jsp").forward(req, resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
doGet(req, resp);
}
}
3. jdbc 大数据的处理
准备：新建 java 工程，名字为 day15。
这里的大数据 LOB(Large Objects) 仅仅指：
- clob 用于存大文本，Text；
- blob 用于存二进制数据，如图像，声音，二进制文件等。
对MySQL而言只有blob，而没有clob，mysql存储大文本采用的是Text，Text和blob分别又分为：
- TINYTEXT、TEXT、MEDIUMTEXT和LONGTEXT
- TINYBLOB、BLOB、MEDIUMBLOB和LONGBLOB
对于MySQL中的Text类型，可调用如下方法去存：
// 给个reader流，而不能给String，大数据的处理只能通过流
PreparedStatement.setCharacterStream(index, reader, length);
//注意length长度须设置，并且设置为int型
对MySQL中的Text类型，可调用如下方法获取：
reader = resultSet. getCharacterStream(i);
reader = resultSet.getClob(i).getCharacterStream();
string s = resultSet.getString(i);
例子 Demo1：
前提是准备好 资源文件db.properties，1.txt，mysql-connector-java-5.0.8-bin.jar，创建好day15数据库和 testclob 表(在下面代码里有)，然后在做这个实验。
public class Demo1 {
/**
* 读写大文本 *
* create table testclob ( id varchar(40) primary key, resume text );
* */
@Test
public void insert() throws SQLException, FileNotFoundException {
Connection conn = null;
PreparedStatement st = null;
ResultSet rs = null;
try {
conn = JdbcUtils.getConnection();
String sql = "insert into testclob(id,resume) values(?,?)";
st = conn.prepareStatement(sql);
st.setString(1, "1");
File file = new File("src/1.txt");
FileReader reader = new FileReader(file);
st.setCharacterStream(2, reader, (int) file.length());
int num = st.executeUpdate();
if (num > 0)
System.out.println("插入成功！！");
} finally {
JdbcUtils.release(conn, st, rs);
}
}
@Test
public void read() throws SQLException, IOException {
Connection conn = null;
PreparedStatement st = null;
ResultSet rs = null;
try {
conn = JdbcUtils.getConnection();
String sql = "select id, resume from testclob where id='1'";
st = conn.prepareStatement(sql);
rs = st.executeQuery();
if (rs.next()) {
// String resume = rs.getString("resume"); 不能这样做，内存会崩
Reader reader = rs.getCharacterStream("resume"); //<---重点
FileWriter writer = new FileWriter("e:\1.txt");
try {
int len = 0;
char buffer[] = new char[1024];
while ((len = reader.read(buffer)) > 0) {
writer.write(buffer, 0, len);
}
} finally {
if (reader != null) {
reader.close();
}
if (writer != null) {
writer.close();
}
}
}
} finally {
JdbcUtils.release(conn, st, rs);
}
}
}
db.properties如下：
driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/day15
username=root
password=root
对于MySQL中的BLOB类型，可调用如下方法设置：
PreparedStatement. setBinaryStream(i, inputStream, length);
对MySQL中的BLOB类型，可调用如下方法获取：
InputStream in = resultSet.getBinaryStream(i);
InputStream in = resultSet.getBlob(i).getBinaryStream();
实验所用的表：
create table testclob ( id varchar(40) primary key, image blob );
细节，略。
4. jdbc 实现数据库批处理
小知识： truncate table testbatch; 清除 testbatch 中的所有数据。
下面例子展现了 oracle 的强大。插入 10000006 条记录，mysql 用大约3小时，而 oracle 只用 380秒，即 6 分多钟！
例子(展示了2种批处理的方式)：
第二种方式适合做批量插入和更新，而第一种方式可发不同种的sql语句。实际开发中，第二种用的多！
package cn.itcast.demo;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import org.junit.Test;
import cn.itcast.utils.JdbcUtils;
public class Demo3 {
/*
create table testbatch
(
id varchar(40) primary key,
name varchar(40)
);
*/
//实现批处理第一种方式
@Test
public void test1() throws SQLException{
Connection conn = null;
Statement st = null;
ResultSet rs = null;
try{
conn = JdbcUtils.getConnection();
String sql1 = "insert into testbatch(id,name) values('1','aaa')";
String sql2 = "update testbatch set name='bbb' where id='1'";
st = conn.createStatement(); //list
st.addBatch(sql1);
st.addBatch(sql2);
//[3,4]
st.executeBatch();
st.clearBatch();
}finally{
JdbcUtils.release(conn, st, rs);
}
}
//实现批处理的第二种方式
@Test
public void test2() throws SQLException{
long starttime = System.currentTimeMillis();
Connection conn = null;
PreparedStatement st = null;
ResultSet rs = null;
try{
conn = JdbcUtils.getConnection();
String sql = "insert into testbatch(id,name) values(?,?)"; //作批量插入 批量更新
st = conn.prepareStatement(sql);
for(int i=1;i<=10000006;i++){
st.setString(1, i+"");
st.setString(2, "aa" + i);
st.addBatch();
if(i%1000==0){
st.executeBatch(); // 每1000个sql做成批，向数据库发一次
st.clearBatch(); // 清除 st 维护的 list 中的数据
}
}
st.executeBatch(); // 剩余的部分做成批，最后再向数据库发一次
}finally{
JdbcUtils.release(conn, st, rs);
}
long endtime = System.currentTimeMillis();
System.out.println("总花了：" + (endtime-starttime)/1000 + "秒");
}
}
5. jdbc 获取数据库自动生成的主键和调用存储过程
5.1 数据库自动生成的主键
public class Demo4 {
/**
获取自动生成的主键
use day15;
create table test(
id int primary key auto_increment,
name varchar(40)
);
*/
public static void main(String[] args) throws SQLException {
Connection conn = null;
PreparedStatement st = null;
ResultSet rs = null;
try {
conn = JdbcUtils.getConnection();
String sql = "insert into test(name) values('aaa')";
// 设置st是否能获取自动生成的主键 但下面的设置不起任何作用，不知为啥
st = conn.prepareStatement(sql, Statement.NO_GENERATED_KEYS); //<--
st.executeUpdate();
rs = st.getGeneratedKeys(); // <-- 重点
if(rs.next()){
System.out.println(rs.getInt(1));
}
} finally {
JdbcUtils.release(conn, st, rs);
}
}
}
5.2 jdbc 调用存储过程(procedure) - 金融证券领域用的特多
金融证券领域的开发无法使用 hibernate，因为数据库表结构是保密的，只有存储过程暴露在外。此领域只能通过 jdbc 调用存储过程去获取数据。
存储过程就是数据库那面的方法或者函数。处理数据用。现在，我们有两种方式从数据库中获取我们想要的数据：
- 在数据库中编写存储过程，由该 procedure 把处理后的数据给我们；
- 直接把数据库的数据拉到我们这来，我们通过 java 编写函数来处理数据，最终获取我们想要的数据。
银行的业务，如利息是在数据库中用存储过程来实现的，而不是在数据库外用其他语言如 java，由其他 coder 实现！
试验准备，编写一个存储过程，如下：
use day15;
delimiter $$
CREATE PROCEDURE demoSp(IN inputParam VARCHAR(255), INOUT inOutParam varchar(255))
BEGIN
SELECT CONCAT('zyxw---', inputParam) into inOutParam;
END $$
delimiter ;
得到CallableStatement，并调用存储过程：
CallableStatement cStmt = conn.prepareCall("{call demoSp(?, ?)}");
设置参数，注册返回值，得到输出：
cStmt.setString(1, "abcdefg");
cStmt.registerOutParameter(2, Types.VARCHAR);
cStmt.execute();
System.out.println(cStmt.getString(2));
完整例子：
public class Demo5 {
public static void main(String[] args) throws SQLException {
Connection conn = null;
CallableStatement cStmt = null;
ResultSet rs = null;
try {
conn = JdbcUtils.getConnection();
cStmt = conn.prepareCall("{call demoSp(?,?)}");
cStmt.setString(1, "haha");
cStmt.registerOutParameter(2, Types.VARCHAR);
cStmt.execute();
System.out.println(cStmt.getString(2));
} finally {
JdbcUtils.release(conn, cStmt, rs);
}
}
}
6. ResultSet 对结果集进行滚动
ResultSet 提供了对结果集进行滚动的方法：
- next()：移动到下一行
- Previous()：移动到前一行
- absolute(int row)：移动到指定行
- beforeFirst()：移动resultSet的最前面。
- afterLast() ：移动到resultSet的最后面
可对小数据量内容分页，不可应用于大数据量，因为数据量大时，ResultSet 对象会很大。应该象第 1 节分页实现里讲的那样，你要那些数据，就查询哪些数据进行显示，而不是一次性把所有数据拿回来，封装到 ResultSet 对象中再处理，这种方式若数据量足够大，内存会崩！