源代码文件：Web App Libraries/struts2-core-2.3.15.3.jar/struts-default.xml
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拦截器modelDriven： <interceptor |
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拦截器params： <interceptor |
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拦截器prepare： <interceptor |
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拦截器栈： <interceptor-stack <interceptor-ref <interceptor-ref <interceptor-ref <interceptor-ref <interceptor-ref <interceptor-ref <param </interceptor-ref> <interceptor-ref <interceptor-ref <interceptor-ref <interceptor-ref <interceptor-ref <interceptor-ref <interceptor-ref <interceptor-ref <param </interceptor-ref> <interceptor-ref <interceptor-ref <param </interceptor-ref> <interceptor-ref <param </interceptor-ref> </interceptor-stack> |
ModelDriven拦截器的作用：
当用户触发每一个请求时，ModelDriven拦截器将调用JavaBean对象的getModel()方法，并把返回值类型压入到ValueStack栈
Params拦截器的作用：
将表单的字段映射到ValueStack栈的栈顶对象的各个属性中。由于此时ValueStack栈的栈顶元素是刚被压入的模型（JavaBean）对象（先用到ModelDriven拦截器，才有这句话），所以该模型将被填充，假设每一个字段在模型里没有匹配的属性，Params拦截器将尝试ValueStack栈中的下一个对象。
PrepareInterceptor拦截器的作用：
u 若Action实现Preparable接口，则Action方法需实现prepare()方法
u PrepareInterceptor拦截器将调用prepare()方法、prepareActionMethodName()方法和prepareDoActionMethodName()方法
u PrepareInterceptor拦截器依据firstCallPrepareDo属性决定获取prepareActionMethodName、prepareDoActionNam的顺序。默认情况下先获取prepareDoActionName(),假设没有该方法，就寻找prepareDoActionMethodName()。
假设找到了相应的方法就调用该方法。
u PrepareInterceptor拦截器会依据alwaysInvokePrepare属性决定是否运行prepare()方法
paramsPrepareParamsStack拦截器栈的作用：（參考struts-default.xml配置文件的结构。就知道具体的含义了）。如今具体解析一下：
u paramsPrepareParamsStack从字面上理解来说。这里Stack的拦截器调用的顺序为：首先params,然后prepare,接下来modelDriven。最后在params
u Struts2.0的设计上要求modelDriven在params之前调用，而业务中prepare要负责准备model，准备model又须要參数，这就须要在prepare之前执行params拦截器设置相关參数，这个也就是创建paramsPrepareParamsStack的原因。
u 流程例如以下：
A. Params拦截器首先给action中的相关參数赋值。如id
B. Prepare拦截器运行prepare方法，prepare方法中会依据參数，如id，去调用业务逻辑，设置model对象
C. ModelDriver拦截器将model对象压入ValueStack，这里的model对象就是在prepare中创建的
D. Params拦截器再将參数赋值给model对象
E. Action的业务逻辑运行
请參考以下源码解析：（第一部分是PrepareInterceptor拦截器的操作流程）
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package com.opensymphony.xwork2.interceptor; import com.opensymphony.xwork2.ActionInvocation; import com.opensymphony.xwork2.Preparable; import com.opensymphony.xwork2.util.logging.Logger; import com.opensymphony.xwork2.util.logging.LoggerFactory; import java.lang.reflect.InvocationTargetException; public private private private private private public this.alwaysInvokePrepare = Boolean.parseBoolean(alwaysInvokePrepare); } public this.firstCallPrepareDo = Boolean.parseBoolean(firstCallPrepareDo); } @Override public String doIntercept(ActionInvocation invocation) //获取Action对象 Object action = invocation.getAction(); //推断Action是否实现了preparable接口 if (action try { String[] prefixes; //依据当前拦截器的 firstCallPrepareDo(默觉得 false) if (firstCallPrepareDo) { prefixes = new String[] {ALT_PREPARE_PREFIX, } else { prefixes = new String[] {PREPARE_PREFIX, } //若为 false, //调用前缀方法. PrefixMethodInvocationUtil.invokePrefixMethod(invocation, prefixes); } catch (InvocationTargetException e) { Throwable cause = e.getCause(); if (cause throw (Exception) cause; } else throw (Error) cause; } else { throw e; } } //依据当前拦截器的 alwaysInvokePrepare(默认是 true) if (alwaysInvokePrepare) { ((Preparable) action).prepare(); } } return invocation.invoke(); } } |
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PrefixMethodInvocationUtil.invokePrefixMethod(invocation, prefixes) 方法: |
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package com.opensymphony.xwork2.interceptor; import com.opensymphony.xwork2.ActionInvocation; import com.opensymphony.xwork2.util.logging.Logger; import com.opensymphony.xwork2.util.logging.LoggerFactory; import java.lang.reflect.InvocationTargetException; import java.lang.reflect.Method; public private private private public //获取 Action Object action = actionInvocation.getAction(); //获取要调用的 Action String methodName = actionInvocation.getProxy().getMethod(); if (methodName == // if null returns (possible according to the docs), use the default execute methodName = DEFAULT_INVOCATION_METHODNAME; } //获取前缀方法 Method method = getPrefixedMethod(prefixes, methodName, action); //若方法不为 null, if (method != method.invoke(action, new Object[0]); } } public assert(prefixes != //把方法的首字母变为大写 String capitalizedMethodName =capitalizeMethodName(methodName); //遍历前缀数组 for (String prefixe : prefixes) { String prefixedMethodName = prefixe + capitalizedMethodName; //通过拼接的方式, try { //利用反射获从 action return action.getClass().getMethod(prefixedMethodName, } catch (NoSuchMethodException e) { // hmm -- OK, try next prefix if (LOG.isDebugEnabled()) { LOG.debug("cannot find method [#0] in action [#1]", prefixedMethodName, action.toString()); } } } return } public assert(methodName != return methodName.substring(0, 1).toUpperCase() + methodName.substring(1); } } |
第二部分（ModelDriver拦截器的源码解析）
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package com.opensymphony.xwork2.interceptor; import com.opensymphony.xwork2.ActionInvocation; import com.opensymphony.xwork2.ModelDriven; import com.opensymphony.xwork2.util.CompoundRoot; import com.opensymphony.xwork2.util.ValueStack; public protected public this.refreshModelBeforeResult = val; } @Override public String intercept(ActionInvocation invocation) //获取 Action //public class EmployeeAction implements RequestAware, ModelDriven<Employee> Object action = invocation.getAction(); //推断 action if (action //强制转换为 ModelDriven ModelDriven modelDriven = (ModelDriven) action; //获取值栈 ValueStack stack = invocation.getStack(); //调用 ModelDriven //即调用 EmployeeAction /* public Employee getModel() { employee = new Employee(); return employee; } */ Object model = modelDriven.getModel(); if (model != //把 getModel() stack.push(model); } if (refreshModelBeforeResult) { invocation.addPreResultListener(new RefreshModelBeforeResult(modelDriven, model)); } } return invocation.invoke(); } /** * Refreshes the model instance on the value stack, if it has changed */ protected private Object protected ModelDriven public RefreshModelBeforeResult(ModelDriven action, Object model) { this.originalModel = model; this.action = action; } public ValueStack stack = invocation.getStack(); CompoundRoot root = stack.getRoot(); boolean needsRefresh = Object newModel = action.getModel(); // Check to see if the new model instance is already on the stack for (Object item : root) { if (item.equals(newModel)) { needsRefresh = false; } } // Add the new model on the stack if (needsRefresh) { // Clear off the old model instance if (originalModel != root.remove(originalModel); } if (newModel != stack.push(newModel); } } } } } |
细节凝视：
细节一：运行 ParametersInterceptor 的 intercept 方法: 把请求參数的值赋给栈顶对象相应的属性. 若栈顶对象没有相应的属性, 则查询值栈中下一个对象相应的属性...
细节二：getModel 方法不能提供下面实现. 的确会返回一个 Employee 对象到值栈的栈顶. 但当前 Action 的 employee 成员变量却是 null.
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@Override public return } |
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