Servlet如何编写异常呢？
下文讲述常见的Servlet抛出异常的处理方法分享，
实现思路:
1.在web.xml中的exception-type定义相应的异常类型及所对应的处理Servlet
2.在web.xml中使用error-page设置相应的状态码对应的Servlet
例: 使用 ExceptionHandler Servlet处理异常的Servlet
<!-- servlet 定义 -->
<servlet>
<servlet-name>ExceptionHandler</servlet-name>
<servlet-class>com.java265.ExceptionHandler</servlet-class>
</servlet>
<!-- servlet 映射 -->
<servlet-mapping>
<servlet-name>ExceptionHandler</servlet-name>
<url-pattern>/com.java265.ExceptionHandler</url-pattern>
</servlet-mapping>
<!-- error-code 相关的错误页面 -->
<error-page>
<error-code>404</error-code>
<location>/ExceptionHandler</location>
</error-page>
<error-page>
<error-code>403</error-code>
<location>/ExceptionHandler</location>
</error-page>
<!-- exception-type 相关的错误页面 -->
<error-page>
<exception-type>
javax.servlet.ServletException
</exception-type >
<location>/ExceptionHandler</location>
</error-page>
<error-page>
<exception-type>java.io.IOException</exception-type >
<location>/ExceptionHandler</location>
</error-page>
exception-type注意事项:
java.lang.Throwable可以接收所有异常类型
--------------------------------------
如:想配置所有异常所对应的Servlet
<error-page>
<exception-type>java.lang.Throwable</exception-type >
<location>/ExceptionHandler</location>
</error-page>
当我们在web.xml中采用以上配置后，
无论异常还是 403,500,404等状态码，
都会调用 ExceptionHandler Servlet进行相应的处理
例:
ServletHelloWorld.java
package servlet01;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class ServletHelloWorld extends HttpServlet {
private static final long serialVersionUID = 888;
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
resp.sendError(500, "Server Exception!");
}
}
ExceptionHandler.java
package servlet01;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class ExceptionHandler extends HttpServlet {
/**
*
*/
private static final long serialVersionUID = 1L;
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
// TODO Auto-generated method stub
Throwable throwable = (Throwable) req.getAttribute("javax.servlet.error.exception");
Integer statusCode = (Integer) req.getAttribute("javax.servlet.error.status_code");
String servletName = (String) req.getAttribute("javax.servlet.error.servlet_name");
if (servletName == null) {
servletName = "Unknown";
}
String requestUri = (String) req.getAttribute("javax.servlet.error.request_uri");
if (requestUri == null) {
requestUri = "Unknown";
}
// 设置响应内容类型
resp.setContentType("text/html;charset=UTF-8");
PrintWriter out = resp.getWriter();
String title = "Java265教程 Error/Exception 信息";
String docType = "<!DOCTYPE html>\n";
out.println(
docType + "<html>\n" + "<head><title>" + title + "</title></head>\n" + "<body bgcolor=\"#f0f0f0\">\n");
out.println("<h1>Java265教程异常信息实例演示</h1>");
if (throwable == null && statusCode == null) {
out.println("<h2>错误信息丢失</h2>");
out.println("请返回 <a href=\"" + resp.encodeURL("http://localhost:8080/servlet01") + "\">主页</a>。");
} else if (statusCode != null) {
out.println("错误代码 : " + statusCode);
} else {
out.println("<h2>错误信息</h2>");
out.println("Servlet Name : " + servletName + "</br></br>");
out.println("异常类型 : " + throwable.getClass().getName() + "</br></br>");
out.println("请求 URI: " + requestUri + "<br><br>");
out.println("异常信息: " + throwable.getMessage());
}
out.println("</body>");
out.println("</html>");
}
}
web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
<display-name>servlet01</display-name>
<servlet>
<servlet-name>helloWorld</servlet-name>
<servlet-class>servlet01.ServletHelloWorld</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>helloWorld</servlet-name>
<url-pattern>/index</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>ErrorHandler</servlet-name>
<servlet-class>servlet01.ExceptionHandler</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>ErrorHandler</servlet-name>
<url-pattern>/ErrorHandler</url-pattern>
</servlet-mapping>
<!-- error-code 相关的错误页面 -->
<error-page>
<error-code>404</error-code>
<location>/ErrorHandler</location>
</error-page>
<error-page>
<error-code>403</error-code>
<location>/ErrorHandler</location>
</error-page>
<error-page>
<error-code>500</error-code>
<location>/ErrorHandler</location>
</error-page>
<!-- exception-type 相关的错误页面 -->
<error-page>
<exception-type>java.lang.Throwable</exception-type >
<location>/ErrorHandler</location>
</error-page>
</web-app>
运行效果如下图所示:
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