在Java的Struts中判断是否调用AJAX及用拦截器对其优化

Strut2判断是否是AJAX调用
1. AJAX与传统Form表单
实际上，两者一般都是通过HTTP的POST请求。区别是浏览器提交Form表单后，期望服务器返回一个完整的HTML页面。而AJAX调用是由XMLHttpRequest对象（不同浏览器可能不一样）发出，浏览器期望服务器返回HTML片段即可，具体是JSON、XML等都没有要求。返回到浏览器后如何使用，也是由JS脚本自己决定的。

2. 请求是不是AJAX
那么对于服务器端，如何判断一个HTTP请求是不是AJAX调用？这需要看HTTP的Header。

我们可以通过Header中的x-request-with来判断。尽管不同浏览器发送AJAX请求的对象不同，但是如果使用jQuery发送AJAX请求的话，jQuery内部实现ajax的时候，已经加入了标识。jQuery源码中是这样的：xhr.setRequestHeader("X-Requested-With","XMLHttpRequest");
所以，如果项目的前台页面都是通过jQuery发送AJAX请求的话，这样判断是安全的。

下面是HTTP请求携带的Header信息。

普通Form表单提交

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									===MimeHeaders ===

									accept = */*

									referer =http://localhost:8080/user2/toQueryPage.action

									accept-language = zh-CN

									user-agent = Mozilla/4.0 (compatible; MSIE8.0; Windows NT 6.1; WOW64; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; InfoPath.3; .NET4.0C;.NET4.0E)

									accept-encoding = gzip, deflate

									host = localhost:8080

									connection = Keep-Alive

									cache-control = no-cache

AJAX调用（IE）

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									===MimeHeaders ===

									x-requested-with = XMLHttpRequest

									accept-language = zh-cn

									referer =http://localhost:8080/user2/toQueryPage.action

									accept = application/json, text/javascript,*/*; q=0.01

									content-type =application/x-www-form-urlencoded

									accept-encoding = gzip, deflate

									user-agent = Mozilla/4.0 (compatible; MSIE8.0; Windows NT 6.1; WOW64; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; InfoPath.3; .NET4.0C;.NET4.0E)

									host = localhost:8080

									content-length = 57

									connection = Keep-Alive

									cache-control = no-cache

3. 在Action中获得HTTP请求头
在Action类中，通过ServletRequestAware接口获得HttpServletRequest对象，再通过getHeader方法得到我们想要的头信息。

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									public abstract class BaseAction 

									    <ParamVo extends BaseParamVo, ResultVo extends BaseResultVo> 

									      extends ActionSupport 

									        implements ServletRequestAware { 

									  private static final String AJAX_RESULT_NAME = "ajaxResult"; 

									  private static final String XHR_OBJECT_NAME = "XMLHttpRequest"; 

									  private static final String HEADER_REQUEST_WITH = "x-requested-with"; 

									  /** 

									   * Request对象，用来判断请求是否是AJAX调用 

									   */

									  private HttpServletRequest request; 

									  private ParamVo paramVo; 

									  private ResultVo resultVo; 

									  @Override

									  public String execute() { 

									    String resultPage = SUCCESS; 

									    try { 

									      resultVo = doExecute(paramVo); 

									    } 

									    catch (BaseException e) { 

									      resultPage = ERROR; 

									    } 

									    if (XHR_OBJECT_NAME.equals(request.getHeader(HEADER_REQUEST_WITH))) { 

									      resultPage = AJAX_RESULT_NAME; 

									    } 

									    return resultPage; 

									  } 

									}

Struts2性能调优拦截器
当我们在工作中需要实现某些小需求时，不妨先进行下简单的调研，看看正在使用的开源框架是否已经具备了我们需要的功能，这样就不用重复发明轮子了。
下面以性能测试为例，看看如何调查Struts2框架是否具备这种功能。

1. struts-default.xml

因为Struts2的许多核心功能都是基于内部拦截器来实现的，所以我们首先要看看它是否有性能调优相关的拦截器。这就需要查看strut2-core-2.3.1.2.jar中的默认配置文件struts-default.xml了。

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									<span style="white-space:pre"> </span><interceptor name="alias" class="com.opensymphony.xwork2.interceptor.AliasInterceptor"/> 

									      <interceptor name="autowiring" class="com.opensymphony.xwork2.spring.interceptor.ActionAutowiringInterceptor"/> 

									      <interceptor name="chain" class="com.opensymphony.xwork2.interceptor.ChainingInterceptor"/> 

									      <interceptor name="conversionError" class="org.apache.struts2.interceptor.StrutsConversionErrorInterceptor"/> 

									      <interceptor name="cookie" class="org.apache.struts2.interceptor.CookieInterceptor"/> 

									      <interceptor name="clearSession" class="org.apache.struts2.interceptor.ClearSessionInterceptor" /> 

									      <interceptor name="createSession" class="org.apache.struts2.interceptor.CreateSessionInterceptor" /> 

									      <interceptor name="debugging" class="org.apache.struts2.interceptor.debugging.DebuggingInterceptor" /> 

									      <interceptor name="execAndWait" class="org.apache.struts2.interceptor.ExecuteAndWaitInterceptor"/> 

									      <interceptornameinterceptorname="exception" class="com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor"/> 

									      <interceptor name="fileUpload" class="org.apache.struts2.interceptor.FileUploadInterceptor"/> 

									      <interceptor name="i18n" class="com.opensymphony.xwork2.interceptor.I18nInterceptor"/> 

									      <interceptor name="logger" class="com.opensymphony.xwork2.interceptor.LoggingInterceptor"/> 

									      <interceptor name="modelDriven" class="com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor"/> 

									      <interceptor name="scopedModelDriven" class="com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor"/> 

									      <interceptor name="params" class="com.opensymphony.xwork2.interceptor.ParametersInterceptor"/> 

									      <interceptor name="actionMappingParams" class="org.apache.struts2.interceptor.ActionMappingParametersInteceptor"/> 

									      <interceptor name="prepare" class="com.opensymphony.xwork2.interceptor.PrepareInterceptor"/> 

									      <interceptor name="staticParams" class="com.opensymphony.xwork2.interceptor.StaticParametersInterceptor"/> 

									      <interceptor name="scope" class="org.apache.struts2.interceptor.ScopeInterceptor"/> 

									      <interceptor name="servletConfig" class="org.apache.struts2.interceptor.ServletConfigInterceptor"/> 

									      <interceptor name="timer" class="com.opensymphony.xwork2.interceptor.TimerInterceptor"/> 

									      <interceptor name="token" class="org.apache.struts2.interceptor.TokenInterceptor"/> 

									      <interceptor name="tokenSession" class="org.apache.struts2.interceptor.TokenSessionStoreInterceptor"/> 

									      <interceptor name="validation" class="org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor"/> 

									      <interceptor name="workflow" class="com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor"/> 

									      <interceptor name="store" class="org.apache.struts2.interceptor.MessageStoreInterceptor" /> 

									      <interceptor name="checkbox" class="org.apache.struts2.interceptor.CheckboxInterceptor" /> 

									      <interceptor name="profiling" class="org.apache.struts2.interceptor.ProfilingActivationInterceptor" /> 

									      <interceptor name="roles" class="org.apache.struts2.interceptor.RolesInterceptor" /> 

									      <interceptor name="annotationWorkflow" class="com.opensymphony.xwork2.interceptor.annotations.AnnotationWorkflowInterceptor" /> 

									      <interceptor name="multiselect" class="org.apache.struts2.interceptor.MultiselectInterceptor" />

Struts2像个百宝箱一样内置了很多拦截器，可以看到profiling很可能就是符合我们需求的拦截器，那现在就打开源码一探究竟。

2. ProfilingActivationInterceptor

org.apache.struts2.interceptor.ProfilingActivationInterceptor.java

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									public class ProfilingActivationInterceptor extendsAbstractInterceptor { 

									  private String profilingKey = "profiling"; 

									  private boolean devMode; 

									  @Inject(StrutsConstants.STRUTS_DEVMODE) 

									  public void setDevMode(String mode) { 

									    this.devMode = "true".equals(mode); 

									  } 

									  @Override

									  public String intercept(ActionInvocationinvocation) throws Exception { 

									    if (devMode) { 

									      Object val =invocation.getInvocationContext().getParameters().get(profilingKey); 

									      if (val != null) { 

									        String sval = (val instanceof String ?(String)val : ((String[])val)[0]); 

									        boolean enable = "yes".equalsIgnoreCase(sval)|| "true".equalsIgnoreCase(sval); 

									        UtilTimerStack.setActive(enable); 

									        invocation.getInvocationContext().getParameters().remove(profilingKey); 

									      } 

									    } 

									    return invocation.invoke(); 

									  } 

									}

从源码中可以看到，只要浏览器发过来的HTTP请求参数中包含profiling=true或者yes，性能拦截器就会开启Timer工具类，打印出Action的执行消耗时间。

3. struts.xml

因为profiling拦截器没有包含到默认的defaultStack中，所以我们要先将它追加到我们自定义的拦截器栈中。

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									<package name="ajax-default" extends="velocity-default"> 

									    <result-types> 

									      <result-type name="json" class="org.apache.struts2.json.JSONResult"/> 

									    </result-types> 

									    <interceptors> 

									      <interceptor-stacknameinterceptor-stackname="ajaxInterceptorStack"> 

									      <interceptor-refnameinterceptor-refname="defaultStack" /> 

									      <interceptor-ref name="profiling"/> 

									      </interceptor-stack> 

									    </interceptors> 

									    <default-interceptor-refnamedefault-interceptor-refname="ajaxInterceptorStack" /> 

									    <global-results> 

									      <result name="comAjaxResult" type="json"> 

									        <param name="excludeNullProperties">true</param> 

									        <param name="root">result</param> 

									        <param name="ignoreHierarchy">false</param> 

									      </result> 

									    </global-results> 

									  </package>

4. userview.js

现在就可以修改AJAX调用参数，追加上profiling参数就可以开始性能调优了。

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									function searchAllUser(){ 

									  jQuery.ajax({ 

									    type:"post", 

									    url: "searchAllUser.action", 

									    processData:true, 

									    dataType:'json', 

									    data:jQuery("#userQueryForm").serialize() + "&profiling=yes", 

									    success:function(data) { 

									    if (data.status == 1) { 

									       alert("创建成功"); 

									       generateTableFromJson("result", data.resultRows); 

									    } else { 

									       alert("创建失败"); 

									    } 

									    } 

									  }); 

									}