javax.servlet Package

javax.servlet

ServletRequest

servlet Container将servletRequest实例传递给servlet的service方法。

public int getContentLength()
// 获取Content type
public java.lang.String getContentType()
// 获取get或post方法传递的value
public java.lang.String getParameter(java.lang.String name)
public java.lang.String getProtocol()

ServletResponse

servlet Container将servletResponse实例传递给servlet的service方法。

  • response.getWriter()获取java.io.PrintWriter实例，处理字符流，默认的编码是ISO-8859-1。
  • response.getOutputStream()获取javax.servlet.ServletOutputStream(继承java.io.OutputStream)实例，处理字节流。
  • response.setContextType()设置content type（content type用于定义网络文件的类型和网页的编码，决定浏览器将以什么形式、什么编码读取这个文件）。
    @Override
public void service(ServletRequest request,
      ServletResponse response) throws ServletException,
      IOException {
  String servletName = servletConfig.getServletName();
  response.setContentType("text/html");
  PrintWriter writer = response.getWriter();
  writer.print("<!DOCTYPE html>"
          + "<html>"
          + "<body>Hello from " + servletName 
          + "</body>"
          + "</html>");
}

ServletConfig

servlet Container初始话servlet时，通过init方法，将ServletConfig实例传递给servlet。

通过init方法，获取ServletConfig并赋值给成员变量

private transient ServletConfig servletConfig;

  @Override
  public void init(ServletConfig servletConfig)
          throws ServletException {
      this.servletConfig = servletConfig;
  }

servletConfig可获取初始化参数（init-param）给servlet。

java.lang.String getInitParameter(java.lang.String name)
java.util.Enumeration<java.lang.String> getInitParameterNames()
java.lang.String servletConfig.getServletName();
// 获取servletContext实例
javax.servlet.ServletContext servletConfig.getServletContext();

例

@WebServlet(name = "ServletConfigDemoServlet", 
    urlPatterns = { "/servletConfigDemo" },
    initParams = {
        @WebInitParam(name="admin", value="Harry Taciak"),
        @WebInitParam(name="email", value="[email protected]")
    }
)
public class ServletConfigDemoServlet implements Servlet {
    private transient ServletConfig servletConfig;

    @Override
    public ServletConfig getServletConfig() {
        return servletConfig;
    }

    @Override
    public void init(ServletConfig servletConfig) 
            throws ServletException {
        this.servletConfig = servletConfig;
    }

    @Override
    public void service(ServletRequest request, 
            ServletResponse response)
            throws ServletException, IOException {
        ServletConfig servletConfig = getServletConfig();
        String admin = servletConfig.getInitParameter("admin");
        String email = servletConfig.getInitParameter("email");
        response.setContentType("text/html");
        PrintWriter writer = response.getWriter();
        writer.print("<!DOCTYPE html>"
                + "<html>"
                + "<body>" 
                + "Admin:" + admin 
                + "<br/>Email:" + email
                + "</body></html>");
    }

    @Override
    public String getServletInfo() {
        return "ServletConfig demo";
    }

    @Override
    public void destroy() {
    }    
}

ServletContext

一个web app，只有一个context。分布式环境下，一个web app部署在多个container中，则一个JVM有一个context。

两种方法获取ServletContext实例：

// 通过request获取
request.getServletContext();
// 通过servletConfig实例获取
servletConfig.getServletContext();

存储在servletContext中的对象被称为attributes

ServletContext提供如下方法处理attributes

java.lang.Object getAttribute(java.lang.String name)
java.util.Enumeration<java.lang.String> getAttributeNames()
void setAttribute(java.lang.String name, java.lang.Object object)
void removeAttribute(java.lang.String name)

GenericServlet

实现了Servlet和ServletConfig接口，主要完成如下任务：

可通过getServletConfig方法获取servletConfig实例

提供servlet接口除service外所有方法的默认实现。

包装servletConfig的方法。

例

@WebServlet(name = "GenericServletDemoServlet", 
    urlPatterns = { "/generic" },
    initParams = {
        @WebInitParam(name="admin", value="Harry Taciak"),
        @WebInitParam(name="email", value="[email protected]")
    }
)
public class GenericServletDemoServlet extends GenericServlet {

    private static final long serialVersionUID = 62500890L;

    @Override
    public void service(ServletRequest request, 
            ServletResponse response)
            throws ServletException, IOException {
        ServletConfig servletConfig = getServletConfig();
        String admin = servletConfig.getInitParameter("admin");
        String email = servletConfig.getInitParameter("email");
        response.setContentType("text/html");
        PrintWriter writer = response.getWriter();
        writer.print("<!DOCTYPE html>"
                + "<html><head></head><body>" 
                + "Admin:" + admin
                + "<br/>Email:" + email
                + "</body></html>");
    }
}

annotations

配置servlet&servlet-mapping

@WebServlet(name = "MyServlet", urlPatterns = { "/my" })

配置init-param

@WebServlet(name = "ServletConfigDemoServlet", 
    urlPatterns = { "/servletConfigDemo" },
    initParams = {
        @WebInitParam(name="admin", value="Harry Taciak"),
        @WebInitParam(name="email", value="[email protected]")
    }
)

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