JavaWeb05_Servlet

亦凉 2023-01-11 08:51 129阅读 0赞

*  **编写Servlet 程序示例：**

1.  编写一个类去实现 Servlet 接口，并实现 service 方法：

public class MyServlet implements Servlet{ 
    	
    	@Override
    	public void init(ServletConfig config) throws ServletException { 
    		System.out.println("----init----第一次访问时调用");
    	}
    
    	@Override
    	public ServletConfig getServletConfig() { 
    		return null;
    	}
    
    	@Override
    	public String getServletInfo() { 
    		return null;
    	}
    
    	@Override
    	public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException { 
    		System.out.println("----Service----");
    		res.setContentType("text/html;charset=UTF-8");
    		res.getWriter().write("你好, BLU!");
    	}
    	
    	@Override
    	public void destroy() { 
    		System.out.println("----destory----");
    	}
    
    }

1.  在 web.xml 中配置映射地址

<servlet>
    	<servlet-name>myServlet</servlet-name>
    	<servlet-class>com.blu.servlet.MyServlet</servlet-class>
    </servlet>
    <servlet-mapping>
    	<servlet-name>myServlet</servlet-name>
    	<url-pattern>/test</url-pattern>
    </servlet-mapping>

1.  访问测试  
    ![在这里插入图片描述][20210126113609345.png]

--------------------

*  **Servlet 的生命周期**

1.  浏览器访问 Servlet，Tomcat 查询当前 Servlet 的实例化对象是否存在，若不存在则通过反射机制动态创建对象（无参构造函数），若存在则直接执行第 3 步
2.  调用 init 方法完成初始化操作
3.  调用 service 方法完成业务逻辑操作
4.  关闭 tomcat 时，会调用 destory 方法释放当前对象所占用的资源

--------------------

*  **基于注解的方式配置 Servlet**

传统基于 xml 的配置：

以上配置可使用以下注解来代替（条件：Servlet 版本在 3.0 以上）：

@WebServlet(name="myServlet",urlPatterns="/test")

--------------------

*  **ServletConfig 接口**

ServletConfig 接口方法：

getServletName()			返回 当前Servlet 的名称
    getInitParameter()			根据（当前Servlet的）初始化参数名获取参数值
    getInitParameterNames()		获取（当前Servlet的）初始化参数名的 Enumeration 集合
    getServletContext()			获取 Servlet 的上下文对象 ServletContext

示例：

@Override
    public void init(ServletConfig config) throws ServletException { 
    	System.out.println(config.getServletName());
    	System.out.println(config.getInitParameter("username"));
    	Enumeration<String> initParameterNames = config.getInitParameterNames();
    	while(initParameterNames.hasMoreElements()) { 
    		System.out.println(initParameterNames.nextElement());
    	}
    	ServletContext context = config.getServletContext();
    }

myServlet
    admin
    password
    username

--------------------

*  **ServletContext**

getContextPath()			获取 Context 路径
    getServerInfo()				获取服务器信息
    getInitParameter()			根据（全局的）初始化参数名获取参数值
    getInitParameterNames()		获取（全局的）初始化参数名的 Enumeration 集合

示例：

<servlet>
    	<servlet-name>myServlet</servlet-name>
    	<servlet-class>com.blu.servlet.MyServlet</servlet-class>
    	<init-param>
    		<param-name>username</param-name>
    		<param-value>admin</param-value>
    	</init-param>
    	<init-param>
    		<param-name>password</param-name>
    		<param-value>123123</param-value>
    	</init-param>
    </servlet>
    <servlet-mapping>
    	<servlet-name>myServlet</servlet-name>
    	<url-pattern>/test</url-pattern>
    </servlet-mapping>
    <context-param>
    	<param-name>username</param-name>
    	<param-value>all</param-value>
    </context-param>
    <context-param>
    	<param-name>password</param-name>
    	<param-value>111111</param-value>
    </context-param>

@Override
    public void init(ServletConfig config) throws ServletException { 
    	ServletContext context = config.getServletContext();
    	System.out.println(context.getContextPath());
    	System.out.println(context.getServerInfo());
    	System.out.println(context.getInitParameter("password"));
    	Enumeration<String> initParameterNames = context.getInitParameterNames();
    	while(initParameterNames.hasMoreElements()) { 
    		System.out.println(initParameterNames.nextElement());
    	}
    }

/bluwebtest
    Apache Tomcat/9.0.31
    111111
    password
    username

--------------------

*  **ServletRequest**

getParameter()					根据请求参数名获取参数值
    getContentType()				获取请求内容类型
    getCharacterEncoding()			获取请求字符编码
    getScheme()						获取请求协议名
    getProtocol()					获取请求协议版本
    getRemoteAddr()					获取客户端ip地址
    getRemoteHost()					获取客户端主机名
    getRemotePort()					获取客户端的端口
    getServerName()					获取请求URL上的主机名
    getServerPort()					获取请求URL上的端口号
    getLocale()						获取客户端Locale相关设置信息
    getLocalAddr()					获取最终接收请求的主机地址
    getLocalName()					获取最终接收请求的主机名
    getLocalPort()					获取最终接收请求的端口
    getServletContext()				获取 ServletContext
    getRequestDispatcher("/demo").forward(req, res)		请求转发

@Override
    public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException { 
    	System.out.println("id:"+ req.getParameter("id"));	
    	System.out.println("contentType:"+ req.getContentType());	
    	System.out.println("characterEncoding:"+ req.getCharacterEncoding());	
    	System.out.println("scheme:"+ req.getScheme());	
    	System.out.println("protocol:"+ req.getProtocol());
    	System.out.println("remoteAddr:"+ req.getRemoteAddr());	
    	System.out.println("remoteHost:"+ req.getRemoteHost());	
    	System.out.println("remotePort:"+ req.getRemotePort());
    	System.out.println("serverName:"+ req.getServerName());
    	System.out.println("serverPort:"+ req.getServerPort());
    	System.out.println("Country:"+ req.getLocale().getCountry());
    	System.out.println("localAddr:"+ req.getLocalAddr());
    	System.out.println("localName:"+ req.getLocalName());
    	System.out.println("localPort:"+ req.getLocalPort());
    	ServletContext context = req.getServletContext();
    				
    }

请求：[http://localhost:8080/bluwebtest/test?id=0001][http_localhost_8080_bluwebtest_test_id_0001]

id:0001
    contentType:null
    characterEncoding:null
    scheme:http
    protocol:HTTP/1.1
    remoteAddr:0:0:0:0:0:0:0:1
    remoteHost:0:0:0:0:0:0:0:1
    remotePort:2743
    serverName:localhost
    serverPort:8080
    Country:CN
    localAddr:0:0:0:0:0:0:0:1
    localName:0:0:0:0:0:0:0:1
    localPort:8080

--------------------

*  **ServletResponse**

getCharacterEncoding()			获取响应字符编码
    getContentType()				获取响应内容类型
    setContentType()				设置响应内容类型
    getWriter()						获取 PrintWriter 对象

@Override
    public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException { 
    
    	System.out.println("CharacterEncoding:"+ res.getCharacterEncoding());
    	System.out.println("ContentType:"+ res.getContentType());
    	res.setContentType("text/html;charset=UTF-8");
    	System.out.println("ContentType:"+ res.getContentType());
    	res.getWriter().write("你好, BLU!");
    		
    }

CharacterEncoding:ISO-8859-1
    ContentType:null
    ContentType:text/html;charset=UTF-8

--------------------

*  **HttpServlet**

@WebServlet("/demo")
    public class MyServlet2 extends HttpServlet { 
    	
    	@Override
    	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { 
    		resp.setContentType("text/html;charset=UTF-8");
    		resp.getWriter().write("你好，BLU!---GET");
    	}
    	
    	@Override
    	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { 
    		resp.setContentType("text/html;charset=UTF-8");
    		resp.getWriter().write("你好，BLU!---POST");
    	}
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0JMVV8xMTE_size_16_color_FFFFFF_t_70]

--------------------

[20210126113609345.png]: /images/20221119/1f4fddf079cd444a833ce605b740131b.png
[http_localhost_8080_bluwebtest_test_id_0001]: http://localhost:8080/bluwebtest/test?id=0001
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0JMVV8xMTE_size_16_color_FFFFFF_t_70]: /images/20221119/8ebd5c0e18ff4a62b3e92a9977b7780c.png