Ajax实现关键字联想和自动补全功能及遇到坑

遇到的小坑

回调函数相对window.onload的摆放位置
给回调函数addData传数据时，如何操作才能将数据传进去

代码实现

前端代码

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>ajax实现关键字联想和自动补全</title>
    <style>
        *{
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }
        #keyWords{
            margin-top: 10px;
            margin-left: 10px;
            width: 300px;
            height: 25px;
            font-size: 20px;
            padding-left: 5px;
        }
        #dataDiv{
            background-color: wheat;
            width: 300px;
            margin-left: 10px;
            display: none;
        }
        #dataDiv p{
            padding-left: 10px;
            padding-top: 7px;
            padding-bottom: 3px;
            cursor: pointer;
        }
        #dataDiv p:hover{
            background-color: cornflowerblue;
            color: white;
        }
    </style>
</head>
<body>
    <!--
        需求:
            1. 给定文本输入框，显示层，显示层里的显示栏
            2. 当用户在文本框里输入数据时，发生keyup事件时，将文本框里的数据，以ajax请求方式提交的到后端
            3. 后端对前端提交的关键字，在数据库里进行模糊查询
            4. 将后端查询到的数据以json格式传给前端
            5. 前端解析后端传来的数据，将数据显示在提示栏里
            6. 当用户点击提示中的某条提示信息时，将提示栏里的信息赋给输入框，隐藏提示层
            注意：1. 凡是输入框里发生keyup事件时，都要进行ajax请求提交，实时获取提示信息
                 2. 输入框信息为空时，也要隐藏提示层
    -->
    <script>
        window.onload = function (){
            //获取dom对象
            input_txt = document.getElementById("keyWords")
            div_data = document.getElementById("dataDiv")
            //为输入框绑定keyup事件
            input_txt.onkeyup = function (){
                //输入框为空，隐藏提示层
                if(this.value.trim() == ""){
                    div_data.style.display = "none"
                }else{
                    //每当keyup时，发送ajax请求，传递文本框内数据
                    var xmlHttpRequest = new XMLHttpRequest();
                    xmlHttpRequest.onreadystatechange = function (){
                        if(this.readyState == 4){
                            if(this.status == 200){
                                //解析后端传来的json数据:[{"content" : "data"}, {}, {}]
                                var jsonArray = JSON.parse(this.responseText)
                                var html = ""
                                for(var i = 0; i < jsonArray.length; i++){
                                    var perData = jsonArray[i].content
                                    //为p标签绑定单击事件,将数据以字符串的形式传给回调函数
                                    html += "<p onclick='addData(\""+perData+"\")'>"+perData+"</p>"
                                }
                                div_data.innerHTML = html
                                div_data.style.display = "block"
                            }else{
                                alert("异常状态码: " + this.status)
                            }
                        }
                    }
                    xmlHttpRequest.open("GET", "/ajax/ajaxAutoComplete?keyWords="+this.value+"", true)
                    xmlHttpRequest.send()
                }
            }
        }
        function addData(perData){
            //完成自动补全
            input_txt.value= perData
            //隐藏提示层
            div_data.style.display = "none"
        }
    </script>
    <input type="text" id="keyWords">
    <div id="dataDiv">
        <!--
        <p>java</p>
        <p>jsp</p>
        <p>service</p>
        <p>servlet</p>
        <p>docker</p>
        <p>linux</p>
        -->
    </div>
</body>
</html>

后端代码

package com.examples.ajax.servlet;
import com.alibaba.fastjson.JSON;
import com.examples.ajax.beans.KeyWords;
import com.examples.ajax.utils.DBUtils;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
@WebServlet("/ajaxAutoComplete")
public class AjaxRequest13 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        //获取前端传来的关键字
        String keyWords = request.getParameter("keyWords");
        //连接数据库，进行模糊查询
        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet rs = null;
        //封装关键字对象
        List<KeyWords> keyWordsList = new ArrayList<>();
        try {
            conn = DBUtils.getConnection();
            String sql = "select content from tb_search where content like ?";
            ps = conn.prepareStatement(sql);
            ps.setString(1, keyWords + "%");
            rs = ps.executeQuery();
            while(rs.next()){
                String content = rs.getString("content");
                //封装成关键字对象
                KeyWords keyWordsObj = new KeyWords(content);
                //将关键字对象封装
                keyWordsList.add(keyWordsObj);
            }
        } catch (SQLException e) {
            throw new RuntimeException(e);
        }finally {
            DBUtils.close(conn, ps, rs);
        }
        //后端数据json化
        String jsonKeyWordsArray = JSON.toJSONString(keyWordsList);
        //返回后端数据
        response.getWriter().write(jsonKeyWordsArray);
    }
}

用到的实体类

package com.examples.ajax.beans;
public class KeyWords {
    private String content;
    public KeyWords() {
    }
    public KeyWords(String content) {
        this.content = content;
    }
    public String getContent() {
        return content;
    }
    public void setContent(String content) {
        this.content = content;
    }
}

自己封装的jdbc工具类

package com.examples.ajax.utils;
import java.sql.*;
import java.util.ResourceBundle;
/**
 * 封装自己的jdbc工具类
 */
public class DBUtils {
    static ResourceBundle bundle = ResourceBundle.getBundle("jdbc");
    static String driver;
    static String url;
    static  String username;
    static  String password;
    static {
        driver = bundle.getString("driver");
        url = bundle.getString("url");
        username = bundle.getString("username");
        password = bundle.getString("password");
        try {
            Class.forName(driver);
        } catch (ClassNotFoundException e) {
            throw new RuntimeException(e);
        }
    }
    private DBUtils(){}
    public static Connection getConnection() throws SQLException {
        return DriverManager.getConnection(url, username, password);
    }
    public static void close(Connection conn, PreparedStatement ps, ResultSet rs){
        if(rs != null){
            try {
                rs.close();
            } catch (SQLException e) {
                throw new RuntimeException(e);
            }
        }
        if(ps != null){
            try {
                ps.close();
            } catch (SQLException e) {
                throw new RuntimeException(e);
            }
        }
        if(conn != null){
            try {
                conn.close();
            } catch (SQLException e) {
                throw new RuntimeException(e);
            }
        }
    }
}