Servlet知识总结(5)——ServletContext

5.ServletContext

web容器启动时，会为每个web程序创建一个对应的ServletContext对象，代表了当前的web应用，即在一个web应用中ServletContext是共有的(唯一)

1.共享数据

在一个Servlet中保存的数据能在另一个Servlet中获取到

public class HelloServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//        this.getServletContext()  servlet上下文
//        this.getInitParameterNames()  初始化参数
//        this.getServletConfig()  servlet配置
        ServletContext context = this.getServletContext();
        String userName = "meeseek";
        context.setAttribute("name",userName);
        System.out.println(" hello");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        super.doGet(req, resp);
    }
}

public class GetServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //解决中文乱码问题
        resp.setContentType("text/html");
        resp.setCharacterEncoding("utf-8");
        
        ServletContext servletContext = this.getServletContext();
        String username = (String) servletContext.getAttribute("name");
        resp.getWriter().print("名字为" + username);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

<servlet>
    <servlet-name>hello</servlet-name>
    <servlet-class>com.shida.servlet.HelloServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>hello</servlet-name>
    <url-pattern>/hello</url-pattern>
  </servlet-mapping>

  <servlet>
    <servlet-name>getc</servlet-name>
    <servlet-class>com.shida.servlet.GetServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>getc</servlet-name>
    <url-pattern>/getc</url-pattern>
  </servlet-mapping>

测试访问结果即可

2.获取初始化参数

<!--  配置一些web初始参数-->
  <context-param>
    <param-name>url</param-name>
    <param-value>jdbc:mysql://localhost:3306/mybatis</param-value>
  </context-param>

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        String url = context.getInitParameter("url");
        resp.getWriter().print(url);
    }

<servlet>
    <servlet-name>sd3</servlet-name>
    <servlet-class>com.shida.servlet.ServletDemo03</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>sd3</servlet-name>
    <url-pattern>/sd3</url-pattern>
  </servlet-mapping>

启动测试结果：

进入的是sd4，但是请求被转发到了sd3，收到的也是sd3的响应

4.读取资源文件

Properties

• 在Java目录下新建properties

  在java目录下新建时，需要在当前module的pom.xml中配置

  <!--在build中配置resources，来防止我们资源导出失败的问题-->
      <build>
          <resources>
              <resource>
                  <directory>src/main/resources</directory>
                  <includes>
                      <include>**/*.properties</include>
                      <include>**/*.xml</include>
                  </includes>
                  <filtering>true</filtering>
              </resource>
              <resource>
                  <directory>src/main/java</directory>
                  <includes>
                      <include>**/*.properties</include>
                      <include>**/*.xml</include>
                  </includes>
                  <filtering>true</filtering>
              </resource>
          </resources>
      </build>
  

  username = dgdfg
  password = fgfegdyhfgjhg
  

  protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
      InputStream stream = this.getServletContext().getResourceAsStream("/WEB-INF/classes/com/shida/servlet/aa.properties");
      Properties properties = new Properties();
      properties.load(stream);
      resp.setContentType("text/html");
      resp.setCharacterEncoding("utf-8");
      String name = properties.getProperty("username");
      String pwd = properties.getProperty("password");
      resp.getWriter().print("用户名：" + name + ",密码：" + pwd);
  
  
  }
  

测试结果为

• 在resources目录下新建properties

  username = root
  password = 123456
  

  protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
      InputStream stream = this.getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties");
      Properties properties = new Properties();
      properties.load(stream);
      resp.setContentType("text/html");
      resp.setCharacterEncoding("utf-8");
      String name = properties.getProperty("username");
      String pwd = properties.getProperty("password");
      resp.getWriter().print("用户名：" + name + ",密码：" + pwd);
  
  
  }
  

  <servlet>
    <servlet-name>sd5</servlet-name>
    <servlet-class>com.shida.servlet.ServletDemo05</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>sd5</servlet-name>
    <url-pattern>/sd5</url-pattern>
  </servlet-mapping>
  

  测试结果为