第一步：填写服务器配置

         登录微信公众平台官网后，在公众平台官网的开发-基本设置页面，勾选协议成为开发者，点击“修改配置”按钮，填写服务器地址（URL）、Token和EncodingAESKey，其中URL是开发者用来接收微信消息和事件的接口URL。Token可由开发者可以任意填写，用作生成签名（该Token会和接口URL中包含的Token进行比对，从而验证安全性）。EncodingAESKey由开发者手动填写或随机生成，将用作消息体加解密密钥。

第二步：验证消息是否来自微信服务器

代码如下：

<?php
/**
  * wechat php test
  */

//define your token
define("TOKEN", "weixin");
$wechatObj = new wechatCallbackapiTest();
$wechatObj->run();

class wechatCallbackapiTest{

	public function run(){
    
    	if ($this->checkSignature() == false) {
    		die('非法请求');
    	}
    	if (isset($_GET['echostr'])) {
    		$echoStr = $_GET['echostr'];
    		echo $echoStr;
        	exit;
    	}else{
    		$this->responseMsg();
    	}
    }

    public function responseMsg()
    {
		//get post data, May be due to the different environments
		$postStr = $GLOBALS["HTTP_RAW_POST_DATA"];
		// $postStr = file_get_contents("php://input");
		file_put_contents('msg.txt', $postStr,FILE_APPEND);

      	//extract post data
		if (!empty($postStr)){
                
              	$postObj = simplexml_load_string($postStr, 'SimpleXMLElement', LIBXML_NOCDATA);
                $fromUsername = $postObj->FromUserName;
                $toUsername = $postObj->ToUserName;
                $keyword = trim($postObj->Content);
                $time = time();
                $textTpl = "<xml>
							<ToUserName><![CDATA[%s]]></ToUserName>
							<FromUserName><![CDATA[%s]]></FromUserName>
							<CreateTime>%s</CreateTime>
							<MsgType><![CDATA[%s]]></MsgType>
							<Content><![CDATA[%s]]></Content>
							<FuncFlag>0</FuncFlag>
							</xml>";             
				if(!empty( $keyword ))
                {
                $contentStr = $this->hf($keyword);
              		$msgType = "text";
                	// $contentStr = "欢迎关注熊本生活!";
                	$resultStr = sprintf($textTpl, $fromUsername, $toUsername, $time, $msgType, $contentStr);
                	echo $resultStr;
                }else{
                	echo "Input something...";
                }

        }else {
        	echo "";
        	exit;
        }

    }

    public function hf($content)
		{
            if ($content == "天气") {
                $contentStr = "有雨";
                return $contentStr;
            }elseif($content == "假期") {
                $contentStr = "三天";
                return $contentStr;
            }else{
                $contentStr = "Sorry...";
                return $contentStr;
            }
		}
	private function checkSignature()
	{
        $signature = $_GET["signature"];
        $timestamp = $_GET["timestamp"];
        $nonce = $_GET["nonce"];	
        		
		$token = TOKEN;
		$tmpArr = array($token, $timestamp, $nonce);
		sort($tmpArr);
		$tmpStr = implode( $tmpArr );
		$tmpStr = sha1( $tmpStr );
		
		if( $tmpStr == $signature ){
			return true;
		}else{
			return false;
		}
	}
}