(三) DWR幾個簡單方法分析

以下分析純屬個人簡潔，不足之處望指教；以下分析在DWR20中，版本不同之處勿怪；

beginBatch()：

    beginBatch方法在engine.js中出現兩次，一次是_execute()代碼段開始，一處就是方法定義處;

dwr.engine.beginBatch = function() {
  if (dwr.engine._batch) {
    dwr.engine._handleError(null, { name:"dwr.engine.batchBegun", message:"Batch already begun" });
    return;
  }
  dwr.engine._batch = dwr.engine._createBatch();
};

方法開始執行，dwr.engine._batch初始爲null，因爲if(null)不成立；執行dwr.engine.createBatch()方法;

官方解釋:生成一個標準的batch對象
dwr.engine._createBatch = function() {
  var batch = {
    map:{
      callCount:0,
      page:window.location.pathname + window.location.search,
      httpSessionId:dwr.engine._getJSessionId(),
      scriptSessionId:dwr.engine._getScriptSessionId()
    },
    charsProcessed:0, paramCount:0,
    parameters:{}, headers:{},
    isPoll:false, handlers:{}, preHooks:[], postHooks:[],
    rpcType:dwr.engine._rpcType,              //dwr.engine._rpcType默認是dwr.engine.XMLHttpRequest,值爲1,即通過ajax調用,默認爲異步
    httpMethod:dwr.engine._httpMethod,
    async:dwr.engine._async,
    timeout:dwr.engine._timeout,
    errorHandler:dwr.engine._errorHandler,
    warningHandler:dwr.engine._warningHandler,     //dwr.engine._warningHandler默認調用dwr.engine.debug(message)方法,即控制檯輸出message
    textHtmlHandler:dwr.engine._textHtmlHandler    //默認爲空;
  };
  if (dwr.engine._preHook) batch.preHooks.push(dwr.engine._preHook);  //_preHook以及_post默認都爲null
  if (dwr.engine._postHook) batch.postHooks.push(dwr.engine._postHook);
  var propname, data;
  if (dwr.engine._headers) {                       //_headers以及_parameters默認爲null,直接返回batch對象
    for (propname in dwr.engine._headers) {
      data = dwr.engine._headers[propname];
      if (typeof data != "function") batch.headers[propname] = data;
    }
  }
  if (dwr.engine._parameters) {
    for (propname in dwr.engine._parameters) {
      data = dwr.engine._parameters[propname];
      if (typeof data != "function") batch.parameters[propname] = data;
    }
  }
  return batch;
};

生成標準dwr.engine._batch對象如下：

以上屬性均爲默認，除httpSessionId   page  scriptSessionId對象；

dwr.engine._getJSessionId()方法如下：

/** @private What is our session id? */
dwr.engine._getJSessionId =  function() {
  var cookies = document.cookie.split(';');
  for (var i = 0; i < cookies.length; i++) {
    var cookie = cookies[i];
    while (cookie.charAt(0) == ' ') cookie = cookie.substring(1, cookie.length);
    if (cookie.indexOf(dwr.engine._sessionCookieName + "=") == 0) {
      return cookie.substring(dwr.engine._sessionCookieName.length + 1, cookie.length);
    }
  }
  return "";
};

解釋下：1.session是服務器端存儲技術，瀏覽器默認通過發送key爲JSESSIONID的cookie，所以如果瀏覽器禁用了SESSION，還可以通過URL重寫將JSESSIONID寫在地址欄使用SESSION；

                2.在tomcat6下可以通過該方法獲取到JSESSIONID,但是在tomcat7下document.cookie無法獲取到JSESSIONID這條cookie,解決方案 tomcat conf目錄下server.xml中對應Context添加useHttpOnly="false"即可，親測可行

 

dwr.engine._getScriptSessionId()方法如下：

/** The function that we use to fetch/calculate a session id */
dwr.engine._getScriptSessionId = function() {
  if (dwr.engine._scriptSessionId == null) {
    dwr.engine._scriptSessionId = dwr.engine._origScriptSessionId + Math.floor(Math.random() * 1000);
  }
  return dwr.engine._scriptSessionId;
};

/** The original page id sent from the server */
dwr.engine._origScriptSessionId = "009659986C0DAED0AE65D2B30BF1FC1E";

所以dwr.engine._getScriptSessionId()爲生成隨機的一串ID標識；

page:window.location.pathname + window.location.search,

dwr.engine._batch.map.Page屬性爲：window.location.pathname爲項目路徑直到？前面值，window.location.search爲?之後參數值;

 

 

dwr.engine._debug()方法分析：

--第一個參數爲控制檯輸出信息,第二個參數爲是否打印堆棧信息  調用console.trace()方法;

/** @private Used internally when some message needs to get to the programmer */
dwr.engine._debug = function(message, stacktrace) {
  var written = false;
  try {
    if (window.console) {
      if (stacktrace && window.console.trace) window.console.trace();
      window.console.log(message);
      written = true;
    }
    else if (window.opera && window.opera.postError) {
      window.opera.postError(message);
      written = true;
    }
  }
  catch (ex) { /* ignore */ }

  if (!written) {
    var debug = document.getElementById("dwr-debug");
    if (debug) {
      var contents = message + "<br/>" + debug.innerHTML;
      if (contents.length > 2048) contents = contents.substring(0, 2048);
      debug.innerHTML = contents;
    }
  }
};

調用方法可以默認有兩種DWREngine._debug('我是debug信息',true)或者dwr.engine._debug('我是debug信息');

效果如下：

 

dwr.engine._handleError()方法如下：

    代碼作用:會彈窗提示錯誤信息,兩個參數 batch以及ex.   ex爲JS對象,指定message屬性爲彈框提示內容,不指定message屬性的話就提示"A server error has occured."

dwr.engine.defaultErrorHandler = function(message, ex) {
  dwr.engine._debug("Error: " + ex.name + ", " + ex.message, true);
  if (message == null || message == "") alert("A server error has occured.");
  // Ignore NS_ERROR_NOT_AVAILABLE if Mozilla is being narky
  else if (message.indexOf("0x80040111") != -1) dwr.engine._debug(message);
  else alert(message);
};

通常batch傳入爲null時,調用_errorHandler方法,默認的_errorHandler爲dwr.engine._errorHandler = dwr.engine.defaultErrorHandler;

dwr.engine.defaultErrorHandler = function(message, ex) {
  dwr.engine._debug("Error: " + ex.name + ", " + ex.message, true);
  if (message == null || message == "") alert("A server error has occured.");
  // Ignore NS_ERROR_NOT_AVAILABLE if Mozilla is being narky
  else if (message.indexOf("0x80040111") != -1) dwr.engine._debug(message);
  else alert(message);
};

實例代碼如下：

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
<script type="text/javascript" src="/DWRDemo/dwr/engine.js"></script>
</head>
<body>
<script type="text/javascript">
	window.onload=function(){
		dwr.engine._handleError(null, { name:"dwr.engine.invalidRpcType", message:"RpcType must be one of dwr.engine.XMLHttpRequest or dwr.engine.IFrame or dwr.engine.ScriptTag" });
		//彈窗提示 message
	}
		</script>
</body>
</html>

運行效果: