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JSP的异常处理
方法1：使用Exception對象
exception對象是Throwable子類的一個實例，只在錯誤頁面中可用。
看一個例子：
<%@ page errorPage="ShowError.jsp" %><html> <head><title>Error Handling Example</title> </head> <body> <% // Throw an exception to invoke the error page int x = 1; if (x == 1) { throw new RuntimeException("Error condition!!!"); } %> </body> </html>使用<%@page errorPage=“XXXXX”%>指令指定一個錯誤頁面ShowError.jsp.
ShowError.jsp的源代碼：
<%@ page isErrorPage="true" %> <html> <head> <title>Show Error Page</title> </head> <body> <h1>Opps...</h1> <p>Sorry, an error occurred.</p> <p>Here is the exception stack trace: </p> <pre> <% exception.printStackTrace(response.getWriter()); %>注意，在瀏覽器里，雖然訪問的是main.jsp, 但實際上顯示的內容已經是ShowError.jsp的實現了：
打印出的錯誤堆棧信息：
java.lang.RuntimeException: Error condition!!! at org.apache.jsp.main_jsp._jspService(main_jsp.java:125) at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70) at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:477) at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:385) at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:329) at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:526) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:678) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:367) at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:860) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1591) at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.lang.Thread.run(Thread.java:745) Opps...方法2：在錯誤頁面中使用JSTL標簽
將ShowError.jsp的內容替換成如下：
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %> <%@page isErrorPage="true" %> <html> <head> <title>Show Error Page</title> </head> <body> <h1>Opps...</h1> <table width="100%" border="1"> <tr valign="top"> <td width="40%"><b>Error:</b></td> <td>${pageContext.exception}</td> </tr> <tr valign="top"> <td><b>URI:</b></td> <td>${pageContext.errorData.requestURI}</td> </tr> <tr valign="top"> <td><b>Status code:</b></td> <td>${pageContext.errorData.statusCode}</td> </tr> <tr valign="top"> <td><b>Stack trace:</b></td> <td> <c:forEach var="trace" items="${pageContext.exception.stackTrace}"> <p>${trace}</p> </c:forEach> </td> </tr> </table> </body> </html>測試結果：
方法3：使用 try…catch塊
如果想要將異常處理放在一個頁面中，并且對不同的異常進行不同的處理，那么就需要使用try…catch塊了。
main.jsp的源代碼：
<html> <head><title>Try...Catch Example</title> </head> <body> <% try{ int i = 1; i = i / 0; out.println("The answer is " + i); } catch (Exception e){ out.println("An exception occurred: " + e.getMessage()); } %> </body> </html>要獲取更多Jerry的原創文章，請關注公眾號"汪子熙":
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