表单POST请求服务器，通过多条件查询获取数据库数据

一、需求

通过表单几个字段查询获取数据库数据，并在jsp页面展示出来
笔者遇到的主要难点：用户查询的时候，表单字段有可能为空字符串("")或者实际值，MySQL查询语句如何写？
想必很多人都会说（包括我之前的想法），用!=""、if(判断语句，正确执行语句，错误执行语句)之类的方法，但是都会遇到类似的问题：
1.第一种方式，如果实际值(value!="")真的不等于空字符串，那么你想获取符合该条件的数据，应该再添加(and 接入号码=value)，这样带来后果是数据不为空字符串的都会被查询出来。
2.第二种方式同样，当实际值(value!="")，赋予(接入号码=value)这没问题。当(value=="")，那么应该赋予什么值，什么条件能够查询出全部数据，或者说什么语句能把这查询条件去掉。
个人能力有限，通过以上方式都未能实现，有哪位大神想到更好的方法麻烦留言告知一二，谢谢！

二、解决方案

导入相关jar包，下载地址：http://repo1.maven.org/maven2/
实体类：

package com.jekin.base;

public class SimInfo {
private String accessPhone;
private String iccid;
private String deviceNumber;
private int allFlow;
private int useFlow;

public SimInfo(String accessPhone, String iccid, String deviceNumber, int allFolw, int useFlow){
this.accessPhone = accessPhone;
this.iccid = iccid;
this.deviceNumber = deviceNumber;
this.allFlow = allFolw;
this.useFlow = useFlow;
}

public String getAccessPhone() {
return accessPhone;
}

public void setAccessPhone(String accessPhone) {
this.accessPhone = accessPhone;
}

public String getIccid() {
return iccid;
}

public void setIccid(String iccid) {
this.iccid = iccid;
}

public String getDeviceNumber() {
return deviceNumber;
}

public void setDeviceNumber(String deviceNumber) {
this.deviceNumber = deviceNumber;
}

public int getAllFlow() {
return allFlow;
}

public void setAllFlow(int allFlow) {
this.allFlow = allFlow;
}

public int getUseFlow() {
return useFlow;
}

public void setUseFlow(int useFlow) {
this.useFlow = useFlow;
}

}

jsp页面(这个自己写，哈哈

)：

<form class="form-inline" role="form">
<div class="form-group form_group">
<label for="exampleInputEmail2">接入号码</label>
<input type="tel" class="form-control" name="phone">
</div>
<div class="form-group form_group">
<label for="exampleInputEmail2">ICCID</label>
<input type="tel" class="form-control" name="iccid">
</div>
<div class="form-group form_group">
<label for="exampleInputEmail2">设备号</label>
<input type="tel" class="form-control" name="number">
</div>
<div class="form-group form_group">
<label for="exampleInputEmail2">开始日期</label>
<input type="date" class="form-control" name="start_time">
</div>
<div class="form-group form_group">
<label for="exampleInputEmail2">结束日期</label>
<input type="date" class="form-control" name="end_time">
</div>
<button type="button" class="btn btn-default form_button">查询</button>
</form>

<script type="text/javascript" src="../js/jquery-3.1.1.min.js"></script>
<script type="text/javascript">
$("button[type='button']").click(function() {
$.ajax({
type: 'POST',
url: "/IoTSystem/servlet/FindServlet",
cache: false,
data: "phone=" + $("input[name='phone']").val() + "&iccid=" + $("input[name='iccid']").val()
+ "&number=" + $("input[name='number']").val() + "&start_time=" + $("input[name='start_time']").val()
+ "&end_time=" + $("input[name='end_time']").val(),
dataType: 'json',
success: function(msg) {
$.each(msg, function(key) {
$('tbody').before(
"<tr>" +
"<td class='text-center'><input type='checkbox' /></td>" +
"<td class='text-center'>" + msg[key].accessPhone + "</td>" +
"<td class='text-center'>" + msg[key].iccid + "</td>" +
"<td class='text-center'>" + msg[key].deviceNumber + "</td>" +
"<td class='text-center'>" + msg[key].allFlow + "</td>" +
"<td class='text-center'>" + msg[key].useFlow + "</td>" +
"</tr>"
);
});
},
error: function(xhr, status, statusText) {
console.log(statusText);
}
});
});
</script>

Servlet类：

package com.jekin.common;

import java.io.IOException;

public class FindServlet extends HttpServlet {

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

response.setCharacterEncoding("UTF-8");
response.setContentType("application/json;character=utf-8");
response.setHeader("Cache-Control", "no-cache");
Map<String, String> map = new HashMap<String, String>();
map.put("接入号码", request.getParameter("phone"));
map.put("ICCID", request.getParameter("iccid"));
map.put("设备号", request.getParameter("number"));
//查询语句
StringBuffer stringBuffer = new StringBuffer("SELECT `接入号码`,ICCID,`设备号`,`总流量(G)`,`使用流量(M)` FROM sim_info ");
//获取查询字段名
Set<String> keys = map.keySet();
//判断条件语句是否第一个，是添加where头部，否则添加and
boolean isFrist = true;
for (String key : keys) {
String value = map.get(key);
if(!value.equals("") && value != null){
if(isFrist){
stringBuffer.append("WHERE " + key + " = " + map.get(key));
isFrist = false;
}else{
stringBuffer.append(" AND " + key + " = " + map.get(key));
}
}
}
//时间段
String start_time_form = request.getParameter("start_time");
String end_time_form = request.getParameter("end_time");
if(!start_time_form.equals("") && !end_time_form.equals("")){
if(isFrist){
stringBuffer.append("WHERE `时间` BETWEEN '" + start_time_form + "' AND '" + end_time_form + "'");
}else{
stringBuffer.append(" AND `时间` BETWEEN '" + start_time_form + "' AND '" + end_time_form + "'");
}
}
MysqlUtil mysqlUtil = new MysqlUtil();
List<SimInfo> simInfos = new ArrayList<SimInfo>();
try {
ResultSet rs = mysqlUtil.execSQL(stringBuffer.toString());
while (rs.next()) {
String accessPhone = rs.getString("接入号码").trim();
String iccid = rs.getString("ICCID").trim();
String deviceNumber = rs.getString("设备号").trim();
int allFolw = Integer.valueOf(rs.getString("总流量(G)").trim());
int useFlow = Integer.valueOf(rs.getString("使用流量(M)").trim());
SimInfo simInfo = new SimInfo(accessPhone, iccid, deviceNumber, allFolw, useFlow);
simInfos.add(simInfo);
}
JSONArray jsonArray = JSONArray.fromObject(simInfos);
PrintWriter printWriter = response.getWriter();
printWriter.write(jsonArray.toString());
printWriter.flush();
printWriter.close();
rs.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
mysqlUtil.closeSQLConnect();
}

}
}

数据库操作类：

package com.jekin.utils;

import java.sql.Connection;

public class MysqlUtil {
private final String dbDriver = "com.mysql.jdbc.Driver";
private final String url = "jdbc:mysql://127.0.0.1:3306/iot";
private final String username = "root";
private final String password = "admin123";
private Connection connection = null;

public MysqlUtil() {
try {
Class.forName("com.mysql.jdbc.Driver");
} catch (ClassNotFoundException e) {
e.printStackTrace();
System.out.println("数据库驱动加载失败");
}
try {
connection = DriverManager.getConnection(url, username, password);
} catch (SQLException e) {
e.printStackTrace();
System.out.println("数据库连接失败");
}
}

// 执行各种SQL语句的方法
public ResultSet execSQL(String sql, Object... args) throws SQLException {
PreparedStatement pStatement = connection.prepareStatement(sql);
// 为pStement对象设置SQL参数值
for (int i = 0; i < args.length; i++) {
pStatement.setObject(i + 1, args[i]);
}
pStatement.execute();
// 返回结果集，如果执行的SQL语句不返回结果集，则返回null
return pStatement.getResultSet();
}

public void closeSQLConnect() {
if (connection != null) {
try {
connection.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}

}