首页 > 代码库 > 从源代码剖析modelDriven拦截器和params拦截器和拦截器prepare 和paramsPrepareParamsStack拦截器栈（使您的Struts2代码更加简洁——怎样培养框架设计能力

从源代码剖析modelDriven拦截器和params拦截器和拦截器prepare 和paramsPrepareParamsStack拦截器栈（使您的Struts2代码更加简洁——怎样培养框架设计能力

2024-07-12 20:09:47   222人阅读

源代码文件出处：Web App Libraries/struts2-core-2.3.15.3.jar/struts-default.xml

拦截器modelDriven：

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

拦截器params：

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

拦截器prepare：

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

拦截器栈：

<interceptor-stackname="paramsPrepareParamsStack">

                <interceptor-refname="exception"/>

                <interceptor-refname="alias"/>

                <interceptor-refname="i18n"/>

                <interceptor-refname="checkbox"/>

                <interceptor-refname="multiselect"/>

                <interceptor-refname="params">

                    <paramname="excludeParams">dojo\..*,^struts\..*,^session\..*,^request\..*,^application\..*,^servlet(Request|Response)\..*,parameters\...*</param>

                </interceptor-ref>

                <interceptor-refname="servletConfig"/>

                <interceptor-refname="prepare"/>

                <interceptor-refname="chain"/>

                <interceptor-refname="modelDriven"/>

                <interceptor-refname="fileUpload"/>

                <interceptor-refname="staticParams"/>

                <interceptor-refname="actionMappingParams"/>

                <interceptor-refname="params">

                    <paramname="excludeParams">dojo\..*,^struts\..*,^session\..*,^request\..*,^application\..*,^servlet(Request|Response)\..*,parameters\...*</param>

                </interceptor-ref>

                <interceptor-refname="conversionError"/>

                <interceptor-refname="validation">

                    <paramname="excludeMethods">input,back,cancel,browse</param>

                </interceptor-ref>

                <interceptor-refname="workflow">

                    <paramname="excludeMethods">input,back,cancel,browse</param>

                </interceptor-ref>

            </interceptor-stack>

 

ModelDriven拦截器的作用：

当用户触发每个请求时，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，因为此时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，如果每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拦截器根据firstCallPrepareDo属性决定获取prepareActionMethodName、prepareDoActionNam的顺序。默认情况下先获取prepareDoActionName(),如果没有该方法，就寻找prepareDoActionMethodName()。如果找到了对应的方法就调用该方法。

u  PrepareInterceptor拦截器会根据alwaysInvokePrepare属性决定是否执行prepare()方法

 

 

paramsPrepareParamsStack拦截器栈的作用：（参考struts-default.xml配置文件的结构，就知道具体的含义了），现在详细解析一下：

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又需要参数，这就需要在prepare之前运行params拦截器设置相关参数，这个也就是创建paramsPrepareParamsStack的原因。

u  流程如下：

A.       Params拦截器首先给action中的相关参数赋值，如id

B.       Prepare拦截器执行prepare方法，prepare方法中会根据参数，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拦截器再将参数赋值给model对象

E.        Action的业务逻辑执行

 

 

请参考下面源代码解析：（第一部分是PrepareInterceptor拦截器的操作流程）

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 class PrepareInterceptor extends MethodFilterInterceptor {

 

    private static final long serialVersionUID = -5216969014510719786L;

 

    private final static String PREPARE_PREFIX ="prepare";

    private final static String ALT_PREPARE_PREFIX ="prepareDo";

 

    private boolean alwaysInvokePrepare = true;

private boolean firstCallPrepareDo = false;

 

    public void setAlwaysInvokePrepare(String alwaysInvokePrepare) {

        this.alwaysInvokePrepare = Boolean.parseBoolean(alwaysInvokePrepare);

}

 

    public void setFirstCallPrepareDo(String firstCallPrepareDo) {

        this.firstCallPrepareDo = Boolean.parseBoolean(firstCallPrepareDo);

    }

 

    @Override

    public String doIntercept(ActionInvocation invocation)throws Exception {

        //获取Action对象

Object action = invocation.getAction();

//判断Action是否实现了preparable接口

        if (actioninstanceof Preparable) {

            try {

                String[] prefixes;

//根据当前拦截器的 firstCallPrepareDo(默认为 false)属性确定 prefixes

                if (firstCallPrepareDo) {

                    prefixes = new String[] {ALT_PREPARE_PREFIX,PREPARE_PREFIX};

                } else {

                    prefixes = new String[] {PREPARE_PREFIX,ALT_PREPARE_PREFIX};

                }

//若为 false,则 prefixes: prepare, prepareDo

            //调用前缀方法.

                PrefixMethodInvocationUtil.invokePrefixMethod(invocation, prefixes);

            }

            catch (InvocationTargetException e) {

 

                Throwable cause = e.getCause();

                if (causeinstanceof Exception) {

                    throw (Exception) cause;

                } elseif(cause instanceof Error) {

                    throw (Error) cause;

                } else {

                    throw e;

                }

            }

//根据当前拦截器的 alwaysInvokePrepare(默认是 true)决定是否调用 Action的 prepare 方法

            if (alwaysInvokePrepare) {

                ((Preparable) action).prepare();

            }

        }

        return invocation.invoke();

    }

}

 

 

PrefixMethodInvocationUtil.invokePrefixMethod(invocation, prefixes) 方法:

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 class PrefixMethodInvocationUtil {

   

    private static final Logger LOG = LoggerFactory.getLogger(PrefixMethodInvocationUtil.class);

 

    private static final String DEFAULT_INVOCATION_METHODNAME ="execute";

 

private static final Class[] EMPTY_CLASS_ARRAY =new Class[0];

 

    public static void invokePrefixMethod(ActionInvocation actionInvocation, String[] prefixes)throws InvocationTargetException, IllegalAccessException {

//获取 Action实例

       Object action = actionInvocation.getAction();

       //获取要调用的 Action方法的名字(update)

       String methodName = actionInvocation.getProxy().getMethod();

      

       if (methodName ==null) {

           // 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,则通过反射调用前缀方法      

if (method !=null) {

           method.invoke(action, new Object[0]);

       }

    }

   

    public static Method getPrefixedMethod(String[] prefixes, String methodName, Object action) {

       assert(prefixes !=null);

//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,得到前缀方法名: 第一次 prepareUpdate,第二次prepareDoUpdate           

try {

//利用反射获从 action中获取对应的方法, 若有直接返回. 并结束循环.

                return action.getClass().getMethod(prefixedMethodName,EMPTY_CLASS_ARRAY);

            }

            catch (NoSuchMethodException e) {

                // hmm -- OK, try next prefix

                if (LOG.isDebugEnabled()) {

                    LOG.debug("cannot find method [#0] in action [#1]", prefixedMethodName, action.toString());

                }

            }

        }

       return null;

    }

   

    public static String capitalizeMethodName(String methodName) {

       assert(methodName !=null);

       return methodName.substring(0, 1).toUpperCase() + methodName.substring(1);

    }

 

}

 

 

 

第二部分（ModelDriver拦截器的源代码解析）

 

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 class ModelDrivenInterceptorextends AbstractInterceptor {

 

    protected boolean refreshModelBeforeResult =false;

 

    public void setRefreshModelBeforeResult(boolean val) {

        this.refreshModelBeforeResult = val;

    }

 

    @Override

public String intercept(ActionInvocation invocation)throws Exception {

//获取 Action对象: EmployeeAction对象, 此时该 Action 已经实现了 ModelDriven 接口

    //public class EmployeeAction implements RequestAware, ModelDriven<Employee>

        Object action = invocation.getAction();

//判断 action是否是 ModelDriven的实例

        if (actioninstanceof ModelDriven) {

//强制转换为 ModelDriven类型

            ModelDriven modelDriven = (ModelDriven) action;

//获取值栈

            ValueStack stack = invocation.getStack();

//调用 ModelDriven接口的 getModel()方法

            //即调用 EmployeeAction的 getModel()方法

            /*

            public Employee getModel() {

              employee = new Employee();

              return employee;

           }

            */

            Object model = modelDriven.getModel();

            if (model != null) {

//把 getModel()方法的返回值压入到值栈的栈顶.实际压入的是 EmployeeAction的 employee 成员变量

              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 static class RefreshModelBeforeResultimplements PreResultListener {

        private ObjectoriginalModel = null;

        protected ModelDrivenaction;

 

 

        public RefreshModelBeforeResult(ModelDriven action, Object model) {

            this.originalModel = model;

            this.action = action;

        }

 

        public void beforeResult(ActionInvocation invocation, String resultCode) {

            ValueStack stack = invocation.getStack();

            CompoundRoot root = stack.getRoot();

 

            boolean needsRefresh =true;

            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 !=null) {

                    root.remove(originalModel);

                }

                if (newModel !=null) {

                    stack.push(newModel);

                }

            }

        }

    }

}

 

 

细节注释：

细节一：执行 ParametersInterceptor 的 intercept 方法: 把请求参数的值赋给栈顶对象对应的属性. 若栈顶对象没有对应的属性, 则查询值栈中下一个对象对应的属性...

 

细节二：getModel 方法不能提供以下实现. 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.

@Override

   public Employee getModel() {

      returnnew Employee();

   }

 

从源代码剖析modelDriven拦截器和params拦截器和拦截器prepare 和paramsPrepareParamsStack拦截器栈（使您的Struts2代码更加简洁——怎样培养框架设计能力


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