Servlet

Servlet

一. 创建servlet项目配置内容

• 新建web项目要记得在pom.xml中导入servlet包

    <dependencies>
        <!--        maven可以自动导入导入的jar包所依赖的其他jar-->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>4.0.1</version>
            <!--          <scope>provided</scope> //作用域（范围），这里保留idea会自动报错-->
        </dependency>
    </dependencies>
    
    <!--在 build 中配置 resources，解决资源导出失败问题-->
<!--include 标签指定哪些文件将被匹配，以*作为通配符-->
<!--exclude 标签指定哪些文件将被忽略，以*作为通配符-->
<!--filtering 构建过程中是否对资源进行过滤，默认false-->
<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>

• class代码

public class HelloServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("hello");
    }

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

• web.xml代码

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

• 浏览器访问 http://localhost:8080/servlet_01/hello

• 控制台输出

[2023-01-05 10:46:22,761] 工件 servlet-01:Web exploded: 正在部署工件，请稍候…
[2023-01-05 10:46:23,200] 工件 servlet-01:Web exploded: 工件已成功部署
[2023-01-05 10:46:23,200] 工件 servlet-01:Web exploded: 部署已花费 439 毫秒
hello

二. 解决服务器输出乱码

将

# java.util.logging.ConsoleHandler.encoding = GBK
改为
java.util.logging.ConsoleHandler.encoding = UTF-8

结果服务器没乱码了，但class文件输出还是乱码

破案了

18版的openjdk有毛病，重新下个17版就行了

三. ServletContext使用

3.1 先存储servletContext

• 直接上代码吧，先调类（可能，猜的）
• 定义变量
• 最后建立属性

ServletContext servletContext = this.getServletContext();
String name = "yorha";
servletContext.setAttribute("name",name);

3.2 调用servletContext

• 第一步一样的，先调类
• 然后定义变量
• 用getAttribute方法获取servletContext内容
• 因为setAttributet中存储的类型是object（数组），所以需要强制类型转化，代码如下

        ServletContext servletContext = this.getServletContext();
        String name = (String) servletContext.getAttribute("name");

网页回显代码

        resp.setContentType("text/html");
        resp.setCharacterEncoding("utf-8");
        resp.getWriter().print("用户名："+name);

未访问hello时get回显内容如下

访问hello文件再回访get回显如下

这里补充一下web.xml配置

    <servlet>
        <servlet-name>hello</servlet-name>
        <servlet-class>com.yorha.servlet.HelloServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>hello</servlet-name>
        <url-pattern>/hello</url-pattern>
    </servlet-mapping>
    
    <servlet>
        <servlet-name>get</servlet-name>
        <servlet-class>com.yorha.servlet.GetServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>get</servlet-name>
        <url-pattern>/get</url-pattern>
    </servlet-mapping>

四. getInitParameter获取初始化参数

4.1 基本配置

• web.xml配置内容

<!--    配置web的一些初始化参数-->
    <context-param>
        <param-name>url</param-name>
        <param-value>jdbc:mysql://localhost:3306/mybatis</param-value>
    </context-param>

• class内容

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

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

输出效果

4.2 转发

实现代码

        ServletContext context = this.getServletContext();
/*        RequestDispatcher requestDispatcher = context.getRequestDispatcher("/demo03");//转发路径
        requestDispatcher.forward(req,resp);//调用servlet实现请求*/
//        简洁化
        context.getRequestDispatcher("/demo03").forward(req,resp);

实例图

可以看到路径不同，但都显示demo03的内容

五. InputStream获取资源包

5.1 java代码

ServletContext context = this.getServletContext();
InputStream resourceAsStream = context.getResourceAsStream("/classes/db.properties");
Properties properties = new Properties();
properties.load(resourceAsStream);
String username = properties.getProperty("username");
String password = properties.getProperty("password");

System.out.println(username+":"+password);

5.2 路径

照着target目录来的

5.3 结果╥﹏╥

提示inStream parameter is null

5.4 inStream parameter is null解决办法

• 然后试着去改了pom.xml文件

<build>
    <resources>
        <resource>
            <directory>src/main/resources</directory>
            <includes>
                <include>**/*.properties</include>
                <include>**/*.xml</include>
            </includes>
            <filtering>true</filtering>
        </resource>
    </resources>
</build>

改完发现没啥用

然后去修改java代码中的路径

InputStream resourceAsStream = context.getResourceAsStream("/WEB-INF/classes/db.properties");

添加WEB-INF目录后获取成功了

但很明显target目录下是没WEB-INF目录的，但如果看out文件中就能发现db.properties是在WEB-INF/classes中