防止点击“返回”后重新提交表单;按钮

我有两个页面:

page1.php:
-有一个带有文本框和"提交"按钮的表单。例如:<form name="frm_register" action="page1.php" method="post">

—PHP和mysql代码将文本框的值存储到数据库。在将值提交给数据库后，Javascript会将页面重定向到php2.php。例如:

$query = "INSERT INTO traceuser (username) VALUES ('{$username}')";
$result = mysql_query($query, $connection);
echo '<script language="javascript">window.location="page2.php";</script>';

page2.php

问题:当我按下"返回"按钮时，浏览器会弹出一个警告消息，说表单将被重新提交。如何防止在点击"返回"按钮时重新提交表单?我是否需要清除page1.php的缓存?如何做它与php或javascript或ajax?

---

更新1:感谢您将javascript window.location="page2.php"替换为php header('Location: home2.php');的答案。它解决了80%的问题。剩下的20%的问题如下:

    if (strtotime($_SESSION['servertime']) < time()-3){ //10800 = 3 hours 3600 = 1 hour
                if (($username != "") AND ($username != $_SESSION[username])){
                    $_SESSION['servertime'] = $servertime; 
                    $_SESSION['username'] = $username;
                    $query = "INSERT INTO traceuser (username) VALUES ('{$username}')";
                    $result = mysql_query($query20, $connection);
                    header('Location: page2.php');
                    exit;
                } else {
                    echo "same name"; //problem here
                }
            }else{
                echo "submit multiple data too fast"; //problem here too.
            }
   }

执行以下步骤时出现问题:
1)用户提交数据成功，跳转到page2.php查看记录
2)用户点击"返回"按钮，跳转回page1.php。
3)用户提交数据失败，停留在page1.php。(因为太快或者同名)
4)用户提交数据成功，跳转到page2.php查看记录
5)用户点击"返回"按钮，浏览器提示"表单将被重新提交"

问题出在步骤3。步骤3没有运行header('Location: page2.php');，没有跳转到page2.php。因此，它导致第5步显示警告消息。如何解决这个问题?

---

更新2:我已经找到了解决20%问题的方法，它工作得很好。我使用session['error123']来决定是否要显示错误信息"同名"。我杀死session['error123']如果成功提交数据到数据库或如果成功跳转到page2.php。我还使用header('Location: page1.php');重定向到自己的页面(同一页面)，使页面忘记之前的表单提交。代码示例:

if ($_SESSION['error123'] == "toofast"){
    echo $_SESSION['error123'] ;
}elseif ($_SESSION['error123'] == "samename"){
    echo $_SESSION['error123'] ;
}
if (strtotime($_SESSION['servertime']) < time()-3){ //10800 = 3 hours 3600 = 1 hour
                if (($username != "") AND ($username != $_SESSION['username'])){
                    $_SESSION['username'] = $username;
                    $query = "INSERT INTO traceuser (username) VALUES ('{$username}')";
                    $result = mysql_query($query20, $connection);
                    $_SESSION['error123'] = "aa";
                    header('Location: http://localhost/plekz/page2.php');
                    exit;
                } else {
                    $_SESSION['error123'] = "samename";
                    header('Location: http://localhost/plekz/page1.php');
                    exit;
                }
            }else{
                $_SESSION['error123'] = "toofast";
                header('Location: http://localhost/plekz/page1.php');
                    exit;
            }
        }
    }

注意:你需要缓冲<?php ob_start();?>的输出，因为$_SESSION不能放在header()之前。Buffer将停止包括session在内的所有输出，让header()先发送输出

header('Location: http://example.com/page2.php');

http_redirect("page2.php");

header("Location: http://example.com/page2.php");
exit;

<form id="thisForm">
...form input fields...
<input type="button" onclick="return submitForm('thisForm')"/>
</form>
function submitForm(formId) {
    $.ajax( {
        type: "post",
        url: 'page2.php',
        data: $('#' + formId + ' input').serialize(),
        ... any other Ajax parameters...,
        success: function(data) {
        }
    });
    return false;
}

<?php
 session_start();
 header_remove("Expires");
 header_remove("Cache-Control");
 header_remove("Pragma");
 header_remove("Last-Modified");
?>