servlet 绝对路径和相对路径获取代码

import java.io.*;
import java.text.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class MyServlet extends HttpServlet {

public void doGet(HttpServletRequest req, HttpServletResponse res)
                               throws ServletException, IOException {
    res.setContentType("text/plain; charset=Shift_JIS");
    PrintWriter out = res.getWriter();
    res.setHeader("Content-Language", "ja");

    Locale locale = new Locale("ja", "");
    DateFormat full = DateFormat.getDateTimeInstance(DateFormat.LONG,
                                                     DateFormat.LONG,
                                                     locale);
    out.println("In Japanese:");

    try {
      FileInputStream fis =
        new FileInputStream(req.getRealPath("/HelloWorld.ISO-2022-JP"));
      InputStreamReader isr = new InputStreamReader(fis, "ISO-2022-JP");
      BufferedReader reader = new BufferedReader(isr);
      String line = null;
      while ((line = reader.readLine()) != null) {
        out.println(line);
      }
    }
    catch (FileNotFoundException e) {
      e.printStackTrace();
    }

out.println(full.format(new Date()));
}
}

<?xml version="1.0" encoding="iso-8859-1"?>
<!DOCTYPE web-app
PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
"http://java.sun.com/dtd/web-app_2_3.dtd">
<web-app>

    <servlet><servlet-name>MyServletName</servlet-name>
             <servlet-class>MyServlet</servlet-class>
    </servlet>

    <servlet-mapping><servlet-name>MyServletName</servlet-name>
        <url-pattern>*.htm</url-pattern>
    </servlet-mapping>

</web-app>

判断来自文件路径信息

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class MyServlet extends HttpServlet {

public void doGet(HttpServletRequest req, HttpServletResponse res)
                               throws ServletException, IOException {
    res.setContentType("text/plain");
    PrintWriter out = res.getWriter();

    if (req.getPathInfo() != null) {
      out.println("The file "" + req.getPathInfo() + """);
      out.println("Is stored at "" + req.getPathTranslated() + """);
    }
    else {
      out.println("Path info is null, no file to lookup");
    }
}
}

<?xml version="1.0" encoding="ISO-8859-1"?>

<!DOCTYPE web-app
PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.2//EN"
"http://java.sun.com/j2ee/dtds/web-app_2_2.dtd">

<web-app>
    <servlet><servlet-name>MyServletName</servlet-name>
             <servlet-class>MyServlet</servlet-class>
    </servlet>

    <servlet-mapping><servlet-name>MyServletName</servlet-name>
        <url-pattern>/index.html</url-pattern>
    </servlet-mapping>
</web-app>

补充：Jsp教程,Jsp/Servlet开发工具