表示Servlet的上下文，該接口由容器實現，每個部署到容器的的Web項目都有唯一的ServletContext接口的實例與之關聯，他是包含在ServletConfig實例中的
ServletConfig提供的功能
獲取環境信息
讀取全局參數
訪問靜態資源
保存與讀取全局屬性
動態註冊Servlet，filter，listener
在Servlet中獲取ServletContext的實例
1.在init方法中：ServletConfig中的getServletContext方法
2.在service方法中：
GenericServlet中的getServletContext方法
ServletRequest中的getServletContext方法
得到過後就可以獲取環境信息了，方法請參見api
全局參數的配置與讀取
在web.xml中使用context-param，param-name，param-value等標籤配置的全局參數
訪問靜態資源
package com.ls.javaees1;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Enumeration;
import java.util.Set;
import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@WebServlet(name = "servlet1", urlPatterns = "/servlet1", loadOnStartup = 1)
public class Servlet1 extends HttpServlet {
@Override
public void init(ServletConfig config) throws ServletException {
ServletContext context = config.getServletContext();
System.out.println(context.getServerInfo());
System.out.println(context.getMajorVersion());
System.out.println(context.getMinorVersion());
System.out.println(context.getServletContextName());
System.out.println(context.getContextPath());
System.out.println(context.getVirtualServerName());
Enumeration<String> names = context.getInitParameterNames();
while(names.hasMoreElements()){
String name=names.nextElement();
System.out.println(name+"="+context.getInitParameter(name));
}
try {
URL url=context.getResource("/index.jsp");
System.out.println(url);
} catch (MalformedURLException e) {
e.printStackTrace();
}
InputStream is=context.getResourceAsStream("/index.jsp");
Set<String> paths=context.getResourcePaths("/");
for (String path : paths) {
System.out.println(path);
}
System.out.println(context.getRealPath("/"));
}
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
ServletContext context1 = getServletContext();
ServletContext contex2 = request.getServletContext();
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
out.println("<HTML>");
out.println(" <HEAD><TITLE>A Servlet</TITLE></HEAD>");
out.println(" <BODY>");
out.print(" This is ");
out.print(this.getClass());
out.println(", using the POST method");
out.println(" </BODY>");
out.println("</HTML>");
out.flush();
out.close();
}
}