如何编写一个Servlet处理类并设置其初始化参数

一.Servlet继承体系

Servlet接口：总接口，定义了Servlet的不同生命周期行为

ServletConfig接口：得到对应Servlet的各种参数

GennericServlet类：是一个抽象类，实现了大部分需要的Servlet方法，大多数Servlet行为都在这里实现

HttpServlet类:抽象类，基于HTTP请求的特性，继承自GennericServlet，实现了自己的service()方法

MyTestServlet：自定义处理类，实现具体的doGet().doPost()方法

//使用注解设置初始化参数@WebServlet(value = "/test",loadOnStartup = 0)public class MyTestServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { }}

二.初始化Servlet参数

使用注解初始化@WebServlet

@Target(ElementType.TYPE)@Retention(RetentionPolicy.RUNTIME)@Documentedpublic @interface WebServlet { /** * @return name of the Servlet */ //指定Servlet名字，默认为包名加上类名 String name() default ""; /** * A convenience method, to allow extremely simple annotation of a class. * * @return array of URL patterns * @see #urlPatterns() */语言方法

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//作用与urlPatterns相同，指定Servlet处理的URL但不能与urlPatterns同时出现 String[] value() default {}; /** * @return array of URL patterns to which this Filter applies */ //指定Servlet处理的URL String[] urlPatterns() default {}; /** * @return load on startup ordering hint */ //指定Servlet的加载顺序 int loadOnStartup() default -1; /** * @return array of initialization params for this Servlet */ //指定初始化参数类型是@webinitparam注解数组 WebInitParam[] initParams() default {}; /** * @return asynchronous operation supported by this Servlet */ boolean asyncSupported() default false; /** * @return small icon for this Servlet, if present */ String smallIcon() default ""; /** * @return large icon for this Servlet, if present */ String largeIcon() default ""; /** * @return description of this Servlet, if present */ String description() default ""; /** * @return display name of this Servlet, if present */ String displayName() default "";}

三.获取初始化参数

调用ServletConfig接口中的getInitParameter(String name)方法获取指定的参数值，返回String

/** * Returns a <code>String</code> containing the value of the named * initialization parameter, or <code>null</code> if the parameter does not * exist. * * @param name * a <code>String</code> specifying the name of the * initialization parameter * @return a <code>String</code> containing the value of the initialization * parameter */ public String getInitParameter(String name);

调用ServletConfig接口中的getInitParameterNames()方法获取全部参数，返回Enumeration<String>

/** * Returns the names of the servlet's initialization parameters as an * <code>Enumeration</code> of <code>String</code> objects, or an empty * <code>Enumeration</code> if the servlet has no initialization parameters. * * @return an <code>Enumeration</code> of <code>String</code> objects * containing the names of the servlet's initialization parameters */ public Enumeration<String> getInitParameterNames();