这期内容当中小编将会给大家带来有关怎么在Java中利用Ajax实现一个用户名重复检验功能，文章内容丰富且以专业的角度为大家分析和叙述，阅读完这篇文章希望大家可以有所收获。
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实体类代码：
/**
*
*/
package com.hqj.dao;
/**
* @author HuangQinJian 下午9:12:19 2017年4月23日
*/
public class User {
private int id;
private String name;
private String password;
/**
*
*/
public User() {
super();
// TODO Auto-generated constructor stub
}
/**
* @param id
* @param name
* @param password
*/
public User(int id, String name, String password) {
super();
this.id = id;
this.name = name;
this.password = password;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
@Override
public String toString() {
return "User [name=" + name + ", password=" + password + "]";
}
}数据库操作类代码：
/**
*
*/
package com.hqj.db;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
/**
* @author HuangQinJian 上午9:21:23 2017年4月24日
*/
public class DBConnection {
public static Connection getConn() {
Connection conn = null;
try {
Class.forName("com.MySQL.jdbc.Driver");
conn = DriverManager
.getConnection("jdbc:mysql://localhost/system?user=root&password=729821");
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
}
return conn;
}
public static PreparedStatement prepare(Connection conn, String sql) {
PreparedStatement pstmt = null;
try {
if (conn != null) {
pstmt = conn.prepareStatement(sql);
}
} catch (SQLException e) {
e.printStackTrace();
}
return pstmt;
}
public static PreparedStatement prepare(Connection conn, String sql,
int autoGenereatedKeys) {
PreparedStatement pstmt = null;
try {
if (conn != null) {
pstmt = conn.prepareStatement(sql, autoGenereatedKeys);
}
} catch (SQLException e) {
e.printStackTrace();
}
return pstmt;
}
public static Statement getStatement(Connection conn) {
Statement stmt = null;
try {
if (conn != null) {
stmt = conn.createStatement();
}
} catch (SQLException e) {
e.printStackTrace();
}
return stmt;
}
public static ResultSet getResultSet(Statement stmt, String sql) {
ResultSet rs = null;
try {
if (stmt != null) {
rs = stmt.executeQuery(sql);
}
} catch (SQLException e) {
e.printStackTrace();
}
return rs;
}
public static void executeUpdate(Statement stmt, String sql) {
try {
if (stmt != null) {
stmt.executeUpdate(sql);
}
} catch (SQLException e) {
e.printStackTrace();
}
}
public static void close(Connection conn) {
try {
if (conn != null) {
conn.close();
conn = null;
}
} catch (SQLException e) {
e.printStackTrace();
}
}
public static void close(Statement stmt) {
try {
if (stmt != null) {
stmt.close();
stmt = null;
}
} catch (SQLException e) {
e.printStackTrace();
}
}
public static void close(ResultSet rs) {
try {
if (rs != null) {
rs.close();
rs = null;
}
} catch (SQLException e) {
e.printStackTrace();
}
}
}上面的数据库操作代码相当于一个工具类，大家可以直接使用，不过要记得改数据库账号，密码以及数据库表名：
conn = DriverManager
.getConnection("jdbc:mysql://localhost/system?user=root&password=729821");service类代码：
/**
*
*/
package com.hqj.service;
import java.util.List;
import com.hqj.dao.User;
/**
* @author HuangQinJian 上午9:26:26 2017年4月24日
*/
public interface UserService {
public String checkUserName(String username);
}serviceImpl类代码：
/**
*
*/
package com.hqj.serviceImpl;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;
import com.hqj.dao.User;
import com.hqj.db.DBConnection;
import com.hqj.service.UserService;
/**
* @author HuangQinJian 上午9:29:14 2017年4月24日
*/
public class UserServiceImpl implements UserService {
private Connection conn = null;
private Statement stmt = null;
private PreparedStatement pstmt = null;
DBConnection dbConnection = new DBConnection();
@Override
public String checkUserName(String username) {
conn = DBConnection.getConn();
stmt = DBConnection.getStatement(conn);
String sql = "select * from user where name=" + "'" + username + "'";
System.out.println("用户查询时的SQL：" + sql);
String str = null;
try {
pstmt = conn.prepareStatement(sql);
if (pstmt.executeQuery().next() == true) {
str = "用户名已存在！";
} else {
str = "用户名可用！";
}
} catch (SQLException e) {
e.printStackTrace();
}
return str;
}
}后台代码：
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%@ page import="com.hqj.serviceImpl.UserServiceImpl"%>
<%
String username = request.getParameter("username");
UserServiceImpl u = new UserServiceImpl();
out.println(u.checkUserName(username));
%>前端代码：
利用原生Ajax实现