ajax 通用方法，从thinkphp中拔出来的

<?php

/**
 * 设置页面输出的CONTENT_TYPE和编码
 * @access public
 * @param string $type content_type 类型对应的扩展名
 * @param string $charset 页面输出编码
 * @return void
 */
function setContentType($type, $charset = '') {
    if (headers_sent())
        return;
    if (empty($charset))
        $charset = 'UTF-8';
    $type = strtolower($type);
//    if (isset($this->_types[$type])) //过滤content_type
//        header('Content-Type: ' . $this->_types[$type] . '; charset=' . $charset);

    if (isset($type)) //过滤content_type
        header('Content-Type: ' . $type . '; charset=' . $charset);
}

/**
 * XML编码
 * @param mixed $data 数据
 * @param string $encoding 数据编码
 * @param string $root 根节点名
 * @return string
 */
function xml_encode($data, $encoding = 'utf-8', $root = 'think') {
    $xml = '<?xml version="1.0" encoding="' . $encoding . '"?>';
    $xml .= '<' . $root . '>';
    $xml .= data_to_xml($data);
    $xml .= '</' . $root . '>';
    return $xml;
}

/**
 * 数据XML编码
 * @param mixed $data 数据
 * @return string
 */
function data_to_xml($data) {
    $xml = '';
    foreach ($data as $key => $val) {
        is_numeric($key) && $key = "item >;
        $xml .= "<$key>";
        $xml .= ( is_array($val) || is_object($val)) ? data_to_xml($val) : $val;
        list($key, ) = explode(' ', $key);
        $xml .= "</$key>";
    }
    return $xml;
}

function dump($var, $echo = true, $label = null, $strict = true) {
    $label = ($label === null) ? '' : rtrim($label) . ' ';
    if (!$strict) {
        if (ini_get('html_errors')) {
            $output = print_r($var, true);
            $output = '<pre>' . $label . htmlspecialchars($output, ENT_QUOTES) . '</pre>';
        } else {
            $output = $label . print_r($var, true);
        }
    } else {
        ob_start();
        var_dump($var);
        $output = ob_get_clean();
        if (!extension_loaded('xdebug')) {
            $output = preg_replace('/]=>
(s+)/m', '] => ', $output);
            $output = '<pre>' . $label . htmlspecialchars($output, ENT_QUOTES) . '</pre>';
        }
    }
    if ($echo) {
        echo($output);
        return null;
    } else
        return $output;
}

/**
 * 输出返回数据
 * @access protected
 * @param mixed $data 要返回的数据
 * @param String $type 返回类型 JSON XML
 * @param integer $code HTTP状态
 * @return void
 */
function response($data, $type = '', $code = 200) {
    sendHttpStatus($code);
    exit(encodeData($data, strtolower($type)));
}

/**
 * 编码数据
 * @access protected
 * @param mixed $data 要返回的数据
 * @param String $type 返回类型 JSON XML
 * @return void
 */
function encodeData($data, $type = '') {
    if (empty($data))
        return '';
    if (empty($type))
        $type = $this->_type;
    if ('json' == $type) {
        // 返回JSON数据格式到客户端 包含状态信息
        $data = json_encode($data);
    } elseif ('xml' == $type) {
        // 返回xml格式数据
        $data = xml_encode($data);
    } elseif ('php' == $type) {
        $data = serialize($data);
    }// 默认直接输出
    setContentType($type);
    header('Content-Length: ' . strlen($data));
    return $data;
}

// 发送Http状态信息
function sendHttpStatus($code) {
    static $_status = array(
        // Informational 1xx
        100 => 'Continue',
        101 => 'Switching Protocols',
        // Success 2xx
        200 => 'OK',
        201 => 'Created',
        202 => 'Accepted',
        203 => 'Non-Authoritative Information',
        204 => 'No Content',
        205 => 'Reset Content',
        206 => 'Partial Content',
        // Redirection 3xx
        300 => 'Multiple Choices',
        301 => 'Moved Permanently',
        302 => 'Moved Temporarily ', // 1.1
        303 => 'See Other',
        304 => 'Not Modified',
        305 => 'Use Proxy',
        // 306 is deprecated but reserved
        307 => 'Temporary Redirect',
        // Client Error 4xx
        400 => 'Bad Request',
        401 => 'Unauthorized',
        402 => 'Payment Required',
        403 => 'Forbidden',
        404 => 'Not Found',
        405 => 'Method Not Allowed',
        406 => 'Not Acceptable',
        407 => 'Proxy Authentication Required',
        408 => 'Request Timeout',
        409 => 'Conflict',
        410 => 'Gone',
        411 => 'Length Required',
        412 => 'Precondition Failed',
        413 => 'Request Entity Too Large',
        414 => 'Request-URI Too Long',
        415 => 'Unsupported Media Type',
        416 => 'Requested Range Not Satisfiable',
        417 => 'Expectation Failed',
        // Server Error 5xx
        500 => 'Internal Server Error',
        501 => 'Not Implemented',
        502 => 'Bad Gateway',
        503 => 'Service Unavailable',
        504 => 'Gateway Timeout',
        505 => 'HTTP Version Not Supported',
        509 => 'Bandwidth Limit Exceeded'
    );
    if (isset($_status[$code])) {
        header('HTTP/1.1 ' . $code . ' ' . $_status[$code]);
        // 确保FastCGI模式下正常
        header('Status:' . $code . ' ' . $_status[$code]);
    }
}

//使用方法，可能方法的顺序需要调整一下
$data = 11;
response(array('code' => 1, 'msg' => '查询成功', 'data' => $data), 'json', 200);