java servlet 3 入门
web开发没怎么搞过，还是看好java ee在web开发领域的实力。servlet 3 来了，写个简单的hello world程序，熟悉熟悉。
开发环境：
linux debian jessie + openjdk 7 + tomcat 7,具体安装配置不详述，安装debian官方源里的包即可，简单快捷。
目录结构
web程序的根目录为hello,其目录结构如下：
[java]
hello
– common
– css
– html
– images
– js
– src
`– HelloServlet3.java
`– WEB-INF
– classes
`– HelloServlet3.class
– lib
`– web.xml
[/java]
源代码
HelloServlet3.java
[java]
import java.io.IOException;
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=”helloServlet3”,urlPatterns={“/“},loadOnStartup=1)
public class HelloServlet3 extends HttpServlet{
@Override
protected void doGet(HttpServletRequest request,HttpServletResponse response)
throws ServletException,IOException{
response.setContentType(“text/plain”);
response.getWriter().write(“hello servlet 3!”);
}
@Override
protected void doPost(HttpServletRequest request,HttpServletResponse response)
throws ServletException,IOException{
doGet(request,response);
}
}
[/java]
部署描述符
servlet 3支持使用注解来部署servlet，因此无需再用web.xml来部署servlet。此web应用的web.xml部署描述符只是一个空的骨架，内容如下：
[xml]
此例程使用@WebServlet注解来部署HelloServlet,与在web.xml中使用如下配置部署是一样的。
[java]
[/java]
编译打包
编译
$ javac -classpath /usr/share/java/servlet-api-3.0.jar HelloServlet3.java
编译完成后生成class文件HelloServlet3.class,将其拷贝到WEB-INF/classes/目录下
打包
切换到web应用程序根目录hello，然后执行
$ jar cvf hello.war *
added manifest
adding: common/(in = 0) (out= 0)(stored 0%)
adding: css/(in = 0) (out= 0)(stored 0%)
adding: html/(in = 0) (out= 0)(stored 0%)
adding: images/(in = 0) (out= 0)(stored 0%)
adding: js/(in = 0) (out= 0)(stored 0%)
adding: src/(in = 0) (out= 0)(stored 0%)
adding: src/HelloServlet3.class(in = 923) (out= 532)(deflated 42%)
adding: src/HelloServlet3.java(in = 796) (out= 292)(deflated 63%)
adding: WEB-INF/(in = 0) (out= 0)(stored 0%)
adding: WEB-INF/lib/(in = 0) (out= 0)(stored 0%)
adding: WEB-INF/web.xml(in = 295) (out= 168)(deflated 43%)
adding: WEB-INF/classes/(in = 0) (out= 0)(stored 0%)
adding: WEB-INF/classes/HelloServlet3.class(in = 923) (out= 532)(deflated 42%)
部署访问
将hello.war拷贝到tomcat7默认的虚拟主机目录下
#cp hello.war /var/lib/tomcat7/webapps/
默认配置下hello.war会被展开到一个文件夹hello，这是因为/etc/tomcat7/server.xml里面默认配置的host的unpackWARs属性为true。
用浏览器打开地址http://127.0.0.1/hello,浏览器会输出：
hello servlet 3!