Java doPost()在使用getParameter()时工作，但doGet()总是抛出null..为什么

Java doPost() works when using getParameter(),but doGet() always throws null... WHY?

本文关键字：doGet null 为什么 工作 doPost getParameter Java      更新时间：2023-09-26

我有一个servlet与doGet()和doPost()函数。当我使用getParameter()上doPost()它工作完美，但是当我使用getParameter()内部doGet()它不能得到参数…它说它们是空的。这些是我的代码。

HTML (index . HTML): 

<!DOCTYPE html>
<html>
<head>
    <meta charset="ISO-8859-1">
    <title>JAVA-AJAX Test</title>
    <script type="text/javascript" src="ajaxfunctions.js"></script>
</head>
<body>
    <h1>Enviar POST mediante AJAX</h1>
    <input type="text" id="username" name="username" value="Puma" />
    <input type="password" id="password" name="password" value="Bernal" />
    <input type="button" id="sendpost" name="sendpost" value="Send POST" />
    <hr/>
    <h1>Enviar GET mediante AJAX</h1>
    <input type="text" id="firstname" name="firstname" value="Jose" />
    <input type="text" id="lastname" name="lastname" value="Bernal" />
    <input type="button" id="sendget" name="sendget" value="Send GET" />
</body>

JavaScript (ajaxfunctions.js): 

window.onload = function()
{
    xhr = new XMLHttpRequest();
    //*************************************POST FUNCTIONS************************************************
    var sendpost = document.getElementById("sendpost");
    sendpost.onclick = function()
    {
        var username = document.getElementById("username");
        var password = document.getElementById("password");
        if (username.value == "" || password.value == "")
            alert("Debe ingresar el usuario y la contraseña!");
        else
            enviarDatosPost(username, password);
    }
    function enviarDatosPost(username, password)
    {
        xhr.onreadystatechange = prepararRespuestaPost;
        xhr.open("POST", "Messages", true);
        var datosPost = crearDatosPost(username, password);
        xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
        alert("POST: " + datosPost);
        xhr.send(datosPost);
    }
    function crearDatosPost(username, password)
    {
        var datosPost = "username="+username.value+"&password="+password.value;
        return datosPost;
    }
    function prepararRespuestaPost()
    {
        if (xhr.readyState == 4)
        {
            if (xhr.status == 200)
            {
                alert("XHR responseText: " + xhr.responseText + "'nXHR statusText: " + xhr.statusText);
            }
        }
    }
    //*************************************GET FUNCTIONS************************************************
    var sendget = document.getElementById("sendget");
    sendget.onclick = function()
    {
        var firstname = document.getElementById("firstname");
        var lastname = document.getElementById("lastname");
        if (firstname.value == "" || lastname.value == "")
            alert("Debe ingresar el nombre y el apellido!");
        else
            enviarDatosGet(firstname, lastname);
    }
    function enviarDatosGet(firstname, lastname)
    {
        xhr.onreadystatechange = prepararRespuestaGet;
        xhr.open("GET", "Messages", true);
        var datosGet = crearDatosGet(firstname, lastname);
        xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
        alert("GET: " + datosGet);
        xhr.send(datosGet);
    }
    function crearDatosGet(firstname, lastname)
    {
        var datosGet = "firstname="+firstname.value+"&lastname="+lastname.value;
        return datosGet;
    }
    function prepararRespuestaGet()
    {
        if (xhr.readyState == 4)
        {
            if (xhr.status == 200)
            {
                alert("XHR responseText: " + xhr.responseText + "'nXHR statusText: " + xhr.statusText);
            }
        }
    }
}

Java (Messages.java): 

package com.puma.servlets;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.*;
/**
 * Servlet implementation class Messages
 */
@WebServlet(asyncSupported = true, urlPatterns = { "/Messages" })
public class Messages extends HttpServlet
{
    private static final long serialVersionUID = 1L;
    /**
     * @see HttpServlet#HttpServlet()
     */
    public Messages()
    {
        super();
    }
    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
    {
        String responseData = "";
        String firstname = request.getParameter("firstname");
        String lastname = request.getParameter("lastname"); 
        System.out.println("DATOS - First Name: " + firstname + " / Last name: " + lastname);
        if (firstname.equals("Jose") && lastname.equals("Bernal"))
            responseData = "USUARIO CONOCIDO - Name : " + firstname + " / Last name: " + lastname;
        else
            responseData = "USUARIO DESCONOCIDO - Name: " + firstname + " / Last name: " + lastname;
        System.out.println(responseData);
        OutputStream stream = response.getOutputStream();
        OutputStreamWriter writer = new OutputStreamWriter(stream, "UTF-8");
        response.setCharacterEncoding("UTF-8");
        response.setContentType("text/plain");
        writer.write(responseData);
        writer.flush();
    }
    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
    {
        String responseData = "";
        String user = request.getParameter("username");
        String pass = request.getParameter("password");
        if (user.equals("Puma") && pass.equals("Bernal"))
            responseData = "DATOS CORRECTOS - Username : " + user + " / Password: " + pass;
        else
            responseData = "DATOS INCORRECTOS - Username: " + user + " / Password: " + pass;
        System.out.println(responseData);
        OutputStream stream = response.getOutputStream();
        OutputStreamWriter writer = new OutputStreamWriter(stream, "UTF-8");
        response.setCharacterEncoding("UTF-8");
        response.setContentType("text/plain");
        writer.write(responseData);
        writer.flush();
    }
}

如果你仔细看，POST和GET的结构完全相同。POST工作得很好，但是GET不行。我做错什么了吗?提前感谢!

POST通过在请求体中发送参数来工作。GET处理URL中编码的参数。因此，对于GET部分，您需要像这样将变量附加到URL: myurl?paramname=paramvalue&paramname2=paramvalue3

不要忘记在将参数附加到URL之前对它们进行编码。

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