第五部分 包拆解 4)org.directwebremoting.create包

在dwr.xml中有，<creator>标签负责公开用于Web远程的类和类的方法，实际上最后调用的就是本包下面的script创建类。
creator类型在1.1版本的时候有如下几种，现在是3.0版本了，我查了下源码，种类好像比下面要多（查XXXCreator有多少个）。
new: 用Java的new关键字创造对象。
none: 它不创建对象，看下面的原因。 (v1.1+)
scripted: 通过BSF使用脚本语言创建对象，例如BeanShell或Groovy。
spring: 通过Spring框架访问Bean。
jsf: 使用JSF的Bean。 (v1.1+)
struts: 使用Struts的FormBean。 (v1.1+)
pageflow: 访问Beehive或Weblogic的PageFlow。 (v1.1+)

creator是在什么时候调用的呢？
实际上，在Serlvet加载的时候有个doPost方法，doPost方法调用handle，handle再调用 remotor，remotor最终调用相应的creator,比如NewCreator，creator实际上是执行创建script字符串的工作。
举例来说，我们想在html中某个地方直接显示当前时间的long值，那么我们就可以调用java.util.Date类的getTime()方法。dwr.xml中写法如下：

< dwr >
< allow >
< createcreator = " new " javascript = " JDate " >
< paramname = " class " value = " java.util.Date " />
</ create >
< createcreator = " new " javascript = " Demo " >
< paramname = " class " value = " your.java.Bean " />
</ create >
</ allow >
</ dwr >

我们知道这样所有的/dwr/*所有请求都由这个servlet来处理，那么实际上，浏览器加载
<script type='text/javascript' src='dwr/interface/JDate.js'></script>时，实际上是在触发servlet，这次触发属于系统 触发，不做事的，只有执行javascript调用方法时如：

function getServerDateTime() {
JDate.getTime(handleGetTime);
}
function handleGetTime(dateTime) {
DWRUtil.setValue("date",dateTime);
}

才会触发下面

protected void doGet(HttpServletRequestreq,HttpServletResponseresp) throws IOException,ServletException
{
doPost(req,resp);
}

doGet会调用到doPost

protected void doPost(HttpServletRequestrequest,HttpServletResponseresponse) throws IOException,ServletException
{
try
{
webContextBuilder.set(request,response,getServletConfig(),getServletContext(),container);

UrlProcessorprocessor=container.getBean(UrlProcessor.class);
processor.handle(request,response);
}
finally
{
webContextBuilder.unset();
}
}

在proccessor中我们看到如下代码

public void handle(HttpServletRequestrequest,HttpServletResponseresponse) throws IOException
{
try
{
StringpathInfo=request.getPathInfo();
contextPath=request.getContextPath();

if(pathInfo==null||pathInfo.length()==0||"/".equals(pathInfo))
{
response.sendRedirect(contextPath+request.getServletPath()+indexHandlerUrl);
}
else
{
//LoopthroughalltheknownURLs
for(Entry<String,Object>entry:urlMapping.entrySet())
{
Stringurl=entry.getKey();

//IfthisURLmatches,callthehandler
if(pathInfo.startsWith(url))
{
Handlerhandler=(Handler)entry.getValue();
handler.handle(request,response);
return;
}
}

notFoundHandler.handle(request,response);
}
}
catch(Exceptionex)
{
exceptionHandler.setException(ex);
exceptionHandler.handle(request,response);
}
}

这些handle有多种
1，
/**
* A Handler that supports requests for auth.js
*/
public class AuthHandler extends JavaScriptHandler
2，
/**
* A Handler that supports requests for engine.js
* @author Joe Walker [joe at getahead dot ltd dot uk]
*/
public class EngineHandler extends JavaScriptHandler
3，
/**
* A Handler that supports requests for util.js
* @author Joe Walker [joe at getahead dot ltd dot uk]
*/
public class GiHandler extends JavaScriptHandler
4，
/**
* A handler for interface generation requests
* @author Joe Walker [joe at getahead dot ltd dot uk]
*/
public class InterfaceHandler extends JavaScriptHandler
上面三种都是系统范围的handle，对于我们自己编写的类，应该是触发InterfaceHandler 。

我们再看如下关系
public abstract class CachingFileHandler implements Handler
public abstract class TemplateHandler extends CachingFileHandler
public abstract class JavaScriptHandler extends TemplateHandler
public class InterfaceHandler extends JavaScriptHandler
逐级往上继承

InterfaceHandler，我们看到如下代码，执行顺序-4，里面调用了远程remoter

protected StringgenerateTemplate(HttpServletRequestrequest,HttpServletResponseresponse) throws IOException
{
StringscriptName=request.getPathInfo();
scriptName=scriptName.replace(interfaceHandlerUrl,"");

StringcontextServletPath=request.getContextPath()+request.getServletPath();

if(scriptName.endsWith(PathConstants.EXTENSION_JS))
{
scriptName=scriptName.replace(PathConstants.EXTENSION_JS,"");
if(!LocalUtil.isJavaIdentifier(scriptName))
{
log.debug("Throwingatrequestforscriptwithname:'"+scriptName+"'");
thrownewSecurityException("ScriptnamesmayonlycontainJavaIdentifiers");
}

returnremoter.generateInterfaceScript(scriptName,contextServletPath);
}
elseif(scriptName.endsWith(PathConstants.EXTENSION_SDOC))
{
scriptName=scriptName.replace(PathConstants.EXTENSION_SDOC,"");
if(!LocalUtil.isJavaIdentifier(scriptName))
{
log.debug("Throwingatrequestforscriptwithname:'"+scriptName+"'");
thrownewSecurityException("ScriptnamesmayonlycontainJavaIdentifiers");
}

returnremoter.generateInterfaceSDoc(scriptName,contextServletPath);
}
else
{
log.debug("Throwingatrequestforscriptwithunknownextension:'"+scriptName+"'");
thrownewSecurityException("Unknownextension");
}
}

类JavaScriptHandler代码如下，调用了父类TemplateHandler的generateCachableContent方法执行顺序-2

protected StringgenerateCachableContent(HttpServletRequestrequest,HttpServletResponseresponse) throws IOException
{
Stringoutput=super.generateCachableContent(request,response);

if(debug||compressor==null)
{
returnoutput;
}

try
{
returncompressor.compressJavaScript(output);
}
catch(Exceptionex)
{
log.warn("Compressionsystem("+compressor.getClass().getSimpleName()+")failedtocompressscript",ex);
returnoutput;
}
}

TemplateHandler类代码如下执行顺序-3，里面调用了generateTemplate方法

protected StringgenerateCachableContent(HttpServletRequestrequest,HttpServletResponseresponse) throws IOException
{
Stringtemplate=generateTemplate(request,response);

Map<String,String>replace=getSearchReplacePairs();
if(replace!=null)
{
for(Map.Entry<String,String>entry:replace.entrySet())
{
Stringsearch=entry.getKey();
if(template.contains(search))
{
template=template.replace(search,entry.getValue());
}
}
}

returntemplate;
}

/***/ /**
*Generateatemplatetoundergosearchandreplaceprocessingaccordingto
*thesearchandreplacepairsfrom{@link#getSearchReplacePairs()}.
*@paramrequestTheHTTPrequestdata
*@paramresponseWherewewritetheHTTPresponsedata
*@returnAtemplatestringcontaining${}sectionstobereplaced
*/
protected abstract StringgenerateTemplate(HttpServletRequestrequest,HttpServletResponseresponse) throws IOException;

CachingFileHandler类代码如下，handle方法里面调用了generateCachableContent()方法
执行顺序-1

public void handle(HttpServletRequestrequest,HttpServletResponseresponse) throws IOException
{
if(isUpToDate(request))
{
response.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
return;
}

Stringoutput;

synchronized(scriptCache)
{
Stringurl=request.getPathInfo();
output=scriptCache.get(url);
if(output==null)
{
output=generateCachableContent(request,response);
}
scriptCache.put(url,output);
}

response.setContentType(mimeType);
response.setDateHeader(HttpConstants.HEADER_LAST_MODIFIED,CONTAINER_START_TIME);
response.setHeader(HttpConstants.HEADER_ETAG,ETAG);

PrintWriterout=response.getWriter();
out.println(output);
}

代码有点绕
我们看到在InterfaceHandler类中
有一行代码如下：
remoter.generateInterfaceScript(scriptName, contextServletPath);
如果按例子，对于声明在dwr.xml中的JDate类，scriptName应该是JDate,contextServletPath应该是'dwr/interface/'

执行generateInterfaceScript方法生成相应的字符串，对应于JDate.js
在CachingFileHandler类中的方法handle最后一行如下，
out.println(output);
在这个地方，将返回内容输出到客户端。