struts2源码分析1(part2)-优快云博客

本文链接：https://blog.youkuaiyun.com/iteye_3330/article/details/82044289

本文深入解析 Struts2 的请求流程，从拦截器、Action 执行到 Result 返回的完整过程，包括如何调用 Action 方法、处理异常以及执行不同的 Result 类型。详细介绍了 Struts2 中的拦截器链、Action 执行机制、Result 创建与执行流程，以及如何通过 Ognl 进行值的查找和设置。最后，提供了一段测试程序来验证 Struts2 的核心功能。

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转： http://blog.youkuaiyun.com/accpsz/archive/2010/12/31/6108917.aspx

// this is needed because the result will be executed, then control will return to the Interceptor, which will
             // return above and flow through again
             if ( ! executed) {
                         // 在Result返回之前调用preResultListeners
                 if (preResultListeners != null ) {
                     for (Iterator iterator = preResultListeners.iterator();
                        iterator.hasNext();) {
                        PreResultListener listener = (PreResultListener) iterator.next();

                        String _profileKey = " preResultListener: " ;
                         try {
                            UtilTimerStack.push(_profileKey);
                            listener.beforeResult( this , resultCode);
                        }
                         finally {
                            UtilTimerStack.pop(_profileKey);
                        }
                    }
                }

                 // now execute the result, if we're supposed to
                 if (proxy.getExecuteResult()) {
                    executeResult();
                }

                executed = true ;
            }

             return resultCode;
        }
         finally {
            UtilTimerStack.pop(profileKey);
        }
    }

看程序中的if(interceptors.hasNext())语句，当然，interceptors里存储的是interceptorMapping列表（它包括一个Interceptor和一个name），所有的截拦器必须实现Interceptor的intercept方法，而该方法的参数恰恰又是ActionInvocation，在intercept方法中还是调用invocation.invoke()，从而实现了一个Interceptor链的调用。当所有的Interceptor执行完，最后调用invokeActionOnly方法来执行Action相应的方法。

   protected String invokeAction(Object action, ActionConfig actionConfig) throws Exception {
        String methodName = proxy.getMethod();
        String timerKey = " invokeAction: " + proxy.getActionName();
         try {
            UtilTimerStack.push(timerKey);

             boolean methodCalled = false ;
            Object methodResult = null ;
            Method method = null ;
             try {
                 // 获得需要执行的方法
                method = getAction().getClass().getMethod(methodName, new Class[ 0 ]);
            } catch (NoSuchMethodException e) {
                 // 如果没有对应的方法，则使用do+Xxxx来再次获得方法
                 try {
                    String altMethodName = " do " + methodName.substring( 0 , 1 ).toUpperCase() + methodName.substring( 1 );
                    method = getAction().getClass().getMethod(altMethodName, new Class[ 0 ]);
                } catch (NoSuchMethodException e1) {
                     // well, give the unknown handler a shot
                     if (unknownHandler != null ) {
                         try {
                            methodResult = unknownHandler.handleUnknownActionMethod(action, methodName);
                            methodCalled = true ;
                        } catch (NoSuchMethodException e2) {
                             // throw the original one
                             throw e;
                        }
                    } else {
                         throw e;
                    }
                }
            }

             if ( ! methodCalled) {
                methodResult = method.invoke(action, new Object[ 0 ]);
            }
             // 根据不同的Result类型返回不同值
             // 如输出流Result
             if (methodResult instanceof Result) {
                 this .explicitResult = (Result) methodResult;
                 return null ;
            } else {
                 return (String) methodResult;
            }
        } catch (NoSuchMethodException e) {
             throw new IllegalArgumentException( " The " + methodName + " () is not defined in action " + getAction().getClass() + "" );
        } catch (InvocationTargetException e) {
             // We try to return the source exception.
            Throwable t = e.getTargetException();

             if (actionEventListener != null ) {
                String result = actionEventListener.handleException(t, getStack());
                 if (result != null ) {
                     return result;
                }
            }
             if (t instanceof Exception) {
                 throw (Exception) t;
            } else {
                 throw e;
            }
        } finally {
            UtilTimerStack.pop(timerKey);
        }
    }

好了，action执行完了，还要根据ResultConfig返回到view，也就是在invoke方法中调用executeResult方法。

   private void executeResult() throws Exception {
         // 根据ResultConfig创建Result
        result = createResult();
        String timerKey = " executeResult: " + getResultCode();
         try {
            UtilTimerStack.push(timerKey);
             if (result != null ) {
                 // 这儿正式执行:)
                 // 可以参考Result的实现，如用了比较多的ServletDispatcherResult,ServletActionRedirectResult,ServletRedirectResult
                result.execute( this );
            } else if (resultCode != null && ! Action.NONE.equals(resultCode)) {
                 throw new ConfigurationException( " No result defined for action " + getAction().getClass().getName()
                         + " and result " + getResultCode(), proxy.getConfig());
            } else {
                 if (LOG.isDebugEnabled()) {
                    LOG.debug( " No result returned for action " + getAction().getClass().getName() + " at " + proxy.getConfig().getLocation());
                }
            }
        } finally {
            UtilTimerStack.pop(timerKey);
        }
    }
     public Result createResult() throws Exception {
         if (explicitResult != null ) {
            Result ret = explicitResult;
            explicitResult = null ;;
             return ret;
        }
        ActionConfig config = proxy.getConfig();
        Map results = config.getResults();
        ResultConfig resultConfig = null ;
         synchronized (config) {
             try {
                 // 根据result名称获得ResultConfig，resultCode就是result的name
                resultConfig = (ResultConfig) results.get(resultCode);
            } catch (NullPointerException e) {
            }
             if (resultConfig == null ) {
                 // 如果找不到对应name的ResultConfig，则使用name为*的Result
                resultConfig = (ResultConfig) results.get( " * " );
            }
        }
         if (resultConfig != null ) {
             try {
                 // 参照StrutsObjectFactory的代码
                Result result = objectFactory.buildResult(resultConfig, invocationContext.getContextMap());
                 return result;
            } catch (Exception e) {
                LOG.error( " There was an exception while instantiating the result of type " + resultConfig.getClassName(), e);
                 throw new XWorkException(e, resultConfig);
            }
        } else if (resultCode != null && ! Action.NONE.equals(resultCode) && unknownHandler != null ) {
             return unknownHandler.handleUnknownResult(invocationContext, proxy.getActionName(), proxy.getConfig(), resultCode);
        }
         return null ;
    }
     // StrutsObjectFactory
     public Result buildResult(ResultConfig resultConfig, Map extraContext) throws Exception {
        String resultClassName = resultConfig.getClassName();
         if (resultClassName == null )
             return null ;
         // 创建Result，因为Result是有状态的，所以每次请求都新建一个
        Object result = buildBean(resultClassName, extraContext);
         // 这句很重要，后面将会谈到，reflectionProvider参见OgnlReflectionProvider；
         // resultConfig.getParams()就是result配置文件里所配置的参数<param>

</param>
         // setProperties方法最终调用的是Ognl类的setValue方法
         // 这句其实就是把param名值设置到根对象result上
        reflectionProvider.setProperties(resultConfig.getParams(), result, extraContext);
         if (result instanceof Result)
             return (Result) result;
         throw new ConfigurationException(result.getClass().getName() + " does not implement Result. " );
    }

最后补充一下，Struts2的查找值和设置值都是使用Ognl来实现的。关于Ognl的介绍可以到其官方网站查看http://www.ognl.org/，我在网上也找到另外一篇http://www.iteye.com/topic/254684和http://www.iteye.com/topic/223612。完了来看下面这段小测试程序（其它的Ognl的测试可以自己添加）。

public class TestOgnl {

     private User user;
     private Map context;

    @Before
     public void setUp() throws Exception {

    }

    @Test
     public void ognlGetValue() throws Exception {
    reset();
    Assert.assertEquals( " myyate " , Ognl.getValue( " name " , user));
    Assert.assertEquals( " cares " , Ognl.getValue( " dept.name " , user));
    Assert.assertEquals( " myyate " , Ognl.getValue( " name " , context, user));
    Assert.assertEquals( " contextmap " , Ognl.getValue( " #name " , context, user));
    Assert.assertEquals( " parker " , Ognl.getValue( " #pen " , context, user));
    }

    @Test
     public void ognlSetValue() throws Exception {
    reset();
    Ognl.setValue( " name " , user, " myyateC " );
    Assert.assertEquals( " myyateC " , Ognl.getValue( " name " , user));

    Ognl.setValue( " dept.name " , user, " caresC " );
    Assert.assertEquals( " caresC " , Ognl.getValue( " dept.name " , user));

    Assert.assertEquals( " contextmap " , Ognl.getValue( " #name " , context, user));
    Ognl.setValue( " #name " , context, user, " contextmapC " );
    Assert.assertEquals( " contextmapC " , Ognl.getValue( " #name " , context, user));

    Assert.assertEquals( " parker " , Ognl.getValue( " #pen " , context, user));
    Ognl.setValue( " #name " , context, user, " parkerC " );
    Assert.assertEquals( " parkerC " , Ognl.getValue( " #name " , context, user));
    }

     public static void main(String[] args) throws Exception {
    JUnitCore.runClasses(TestOgnl. class );
    }

     private void reset() {
    user = new User( " myyate " , new Dept( " cares " ));
    context = new OgnlContext();
    context.put( " pen " , " parker " );
    context.put( " name " , " contextmap " );
    }
}

class User {
     public User(String name, Dept dept) {
     this .name = name;
     this .dept = dept;
    }
    String name;
     private Dept dept;
     public Dept getDept() {
         return dept;
    }
     public String getName() {
         return name;
    }
     public void setDept(Dept dept) {
         this .dept = dept;
    }
     public void setName(String name) {
         this .name = name;
    }
}

class Dept {
     public Dept(String name) {
     this .name = name;
    }
     private String name;
     public String getName() {
         return name;
    }
     public void setName(String name) {
         this .name = name;
    }
}

这样，一个Struts2的请求流程基本上就结束了。其实我觉得做项目把Struts2参考文档看两遍就可以了，