Struts提供了一个更简单的方式来处理未捕获的异常,并将用户重定向到一个专门的错误页面。您可以轻松地Struts配置到不同的异常有不同的错误页面。
Struts的异常处理所使用的“exception”拦截容易。“exception”拦截器作为默认的栈的一部分,所以不必做任何额外的配置。它可为准备使用的盒。让我们看到了一个简单的Hello World示例进行一些修改在HelloWorldAction.java文件。在这里,我们特意推出了一个空指针异常在我们HelloWorldAction动作代码。
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package com.yiibai.struts2; import com.opensymphony.xwork2.ActionSupport; public class HelloWorldAction extends ActionSupport{ private String name; public String execute(){ String x = null ; x = x.substring( 0 ); return SUCCESS; } public String getName() { return name; } public void setName(String name) { this .name = name; } } |
让我们 helloWorld.jsp保持内容如下:
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<%@ page contentType= "text/html; charset=UTF-8" %> <%@ taglib prefix= "s" uri= "/struts-tags" %> <html> <head> <title>Hello World</title> </head> <body> Hello World, <s:property value= "name" /> </body> </html> |
以下是内容index.jsp:
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<%@ page language= "java" contentType= "text/html; charset=ISO-8859-1" pageEncoding= "ISO-8859-1" %> <%@ taglib prefix= "s" uri= "/struts-tags" %> <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd" > <html> <head> <title>Hello World</title> </head> <body> <h1>Hello World From Struts2</h1> <form action= "hello" > <label for = "name" >Please enter your name</label><br/> <input type= "text" name= "name" /> <input type= "submit" value= "Say Hello" /> </form> </body> </html> |
struts.xml 应该像这样:
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<? xml version = "1.0" encoding = "UTF-8" ?> <!DOCTYPE struts PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN" "http://struts.apache.org/dtds/struts-2.0.dtd"> < struts > < constant name = "struts.devMode" value = "true" /> < package name = "helloworld" extends = "struts-default" > < action name = "hello" class = "com.yiibai.struts2.HelloWorldAction" method = "execute" > < result name = "success" >/HelloWorld.jsp</ result > </ action > </ package > </ struts > |
现在右击项目名称,并单击Export > WAR File创建一个WAR文件。然后部署此WAR在Tomcat的webapps目录下。最后,启动Tomcat 服务器和尝试访问URL http://localhost:8080/HelloWorldStruts2/index.jsp。这会给出以下画面:
输入一个值“Struts2”,并提交页面。应该看到以下页面:
在上面的例子所示,默认的异常拦截器做了非常出色的处理异常。现在,让我们创建一个专用的错误页面,我们的例外。创建一个文件名为error.jsp 如以下内容:
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<%@ page language= "java" contentType= "text/html; charset=ISO-8859-1" pageEncoding= "ISO-8859-1" %> <%@ taglib prefix= "s" uri= "/struts-tags" %> <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd" > <html> <head> <title></title> </head> <body> This is my custom error page </body> </html> |
Let us now configure Struts to use this this error page in case of an exception. Let us modify thestruts.xml as follows:
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<? xml version = "1.0" encoding = "UTF-8" ?> <!DOCTYPE struts PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN" "http://struts.apache.org/dtds/struts-2.0.dtd"> < struts > < constant name = "struts.devMode" value = "true" /> < package name = "helloworld" extends = "struts-default" > < action name = "hello" class = "com.yiibai.struts2.HelloWorldAction" method = "execute" > < exception-mapping exception = "java.lang.NullPointerException" result = "error" /> < result name = "success" >/HelloWorld.jsp</ result > < result name = "error" >/Error.jsp</ result > </ action > </ package >< br ></ struts > |
在上面的例子所示,现在我们已经配置 Struts使用专用error.jsp的NullPointerException异常。如果现在重新运行该程序,现在看到下面的输出:
根据<exception-mapping…../>元素出现位置的不同,异常映射又可分为两种:
局部异常映射:将<exception-mapping… />元素作为<action…/>元素的子元素配置;
全局异常映射:将<exception-mapping… />元素作为<global-exception-mappings… />元素的子元素配置;
全局异常映射对所有的Action都有效,但局部异常映射仅对该异常映射所在的Action有效。
如果局部异常映射和全局异常映射配置了同一个异常类型,在<action…./>元素内的局部异常映射将覆盖全局异常映射。
Struts.xml
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< package name = "ssh2" extends = "struts-default" > < global-results > < result name = "sql" >/exception.jsp</ result > < result name = "root" >/exception.jsp</ result > </ global-results > < global-exception-mappings > < exception-mapping exception = "java.sql.SQLException" result = "sql" /> < exception-mapping exception = "java.lang.Exception" result = "root" /> </ global-exception-mappings > < action name = "login" class = "loginAction" > < result >/welcome.jsp</ result > < result name = "nullPointer" >/nullPointer.jsp</ result > < exception-mapping exception = "java.lang.NullPointerException" result = "nullPointer" /> </ action > </ package > |
Action
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public class loginAction extends ActionSupport { public String add() throws SQLException { return "toadd" ; } } |
有异常往外抛即可。你也可以在方法里面抛,比如throw SQLException。
我们可以使用Struts2的标签输出异常信息:
输出异常的message属性信息:<s:property value="exception.message" />
输出异常堆栈信息:<s:property value="exceptionStack" />。
有了处理系统异常的基础,我们来看一看自定义异常:
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package com.exception ; public class MyException extends Exception { private String message; public MyException(String message) { super (message); this .message = message ; } public String getMessage() { return message; } public void setMessage(String message) { this .message = message; } } public String execute() throws Exception { if (! "hello" .equals(usename) || ! "world" .equals(password)) { throw new MyException( "用户名或密码错误,您发现了吧!" ); } return "success" ; } |
在action配置中的异常处理
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<struts> < package name= "struts2" extends = "struts-default" > <action name= "login" class = "com.struts2.LoginAction" > <exception-mapping result= "myex" exception= "com.exception.MyException" > </exception-mapping> <result name= "myex" >/error.jsp</result> <result name= "success" >/result.jsp</result> </action> </ package > </struts> |
在全局配置中的异常处理
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<struts> < package name= "struts2" extends = "struts-default" > <global-results> <result name= "myexception1" >/error.jsp</result> </global-results> <global-exception-mappings> <exception-mapping result= "myexception1" exception= "com.exception.MyException" > </exception-mapping> </global-exception-mappings> <action name= "login" class = "com.struts2.LoginAction" > <result name= "success" >/result.jsp</result> </action> </ package > </struts> |
错误页面error.jsp
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<%@ page language= "java" import = "java.util.*" pageEncoding= "UTF-8" %> <%@ taglib prefix= "s" uri= "/struts-tags" %> <html> <body> <!-- 这个exception 是 exception= "com.exception.MyException" --> <s:property value= "exception.message" /> </body> </html> |
总结
局部异常处理比全局异常处理高,并且可覆盖全局异常处理,如果定义了全局异常映射,那么会对所有的Action生效,反之定义了局部异常映射则会对当前Action生效,
如果在全局区域和局部区域定义了相同的异常映射,首先去局部异常区域找result结果页面,如果找到了,则直接跳转到错误结果页面,不管全局有没有相同的结果,都被局部所覆盖,如果在局部区域没找到,则去全局区域找。