Servlet版本
Oracle将Java EE（Java SE还自己保留）交给开源组织，Eclipse基金会接手。但Oracle不允许开源组织使用Java名号，所以Jakarta EE名称于2018.02.26应运而生。
正是因为组织变化，Servlet被割裂为了2个版本，javax.servlet和jakarta.servlet。
javax.servlet已经停止维护，但它仍然是一个非常有用和重要的技术，特别是在许多现有项目中，学习和使用它将为你提供坚实的Web开发基础。
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>javax.servlet-api</artifactId>
<version>3.1.0</version>
<scope>provided</scope>
</dependency>
如果希望使用Jakarta EE 9或更高版本的Servlet API，则需要切换到javax.servlet。
<dependency>
<groupId>jakarta.servlet</groupId>
<artifactId>jakarta.servlet-api</artifactId>
<version>6.0.0</version>
<scope>provided</scope>
</dependency>
本文将基于javax.servlet来介绍Servlet，从Usages来看，它仍然是使用最广泛的。
Servlet API
Servlet API主要有2个包，javax.servlet包含了servlet和web container使用的接口和类。javax.servlet.http包含了http相关的接口和类。
javax.servlet接口列表：
- Servlet
- ServletRequest
- ServletResponse
- RequestDispatcher
- ServletConfig
- ServletContext
- SingleThreadModel
- Filter
- FilterConfig
- FilterChain
- ServletRequestListener
- ServletRequestAttributeListener
- ServletContextListener
- ServletContextAttributeListener
javax.servlet类列表：
- GenericServlet
- ServletInputStream
- ServletOutputStream
- ServletRequestWrapper
- ServletResponseWrapper
- ServletRequestEvent
- ServletContextEvent
- ServletRequestAttributeEvent
- ServletContextAttributeEvent
- ServletException
- UnavailableException
javax.servlet.http接口列表：
- HttpServletRequest
- HttpServletResponse
- HttpSession
- HttpSessionListener
- HttpSessionAttributeListener
- HttpSessionBindingListener
- HttpSessionActivationListener
- HttpSessionContext (deprecated now)
javax.servlet.http类列表：
- HttpServlet
- Cookie
- HttpServletRequestWrapper
- HttpServletResponseWrapper
- HttpSessionEvent
- HttpSessionBindingEvent
- HttpUtils (deprecated now)
Servlet接口
Servlet Interface定义了所有servlet必须具有的行为。主要方法如下：
-
public void init(ServletConfig config) 初始化，只会被web container调用1次
-
public void service(ServletRequest request, ServletResponse response) 接收请求，返回响应，每次请求都会调用1次
-
public void destroy() 销毁，只会被web container调用1次
-
public ServletConfig getServletConfig() Servlet配置
-
public String getServletInfo() Servlet信息
以下是代码示例：
import java.io.*;
import javax.servlet.*;
public class First implements Servlet {
ServletConfig config = null;
/**
* 初始化
* @param config
*/
public void init(ServletConfig config) {
this.config = config;
System.out.println("servlet is initialized");
}
/**
* 服务
* @param req
* @param res
* @throws IOException
* @throws ServletException
*/
public void service(ServletRequest req, ServletResponse res)
throws IOException, ServletException {
res.setContentType("text/html");
PrintWriter out = res.getWriter();
out.print("<html><body>");
out.print("<b>hello simple servlet</b>");
out.print("</body></html>");
}
/**
* 销毁
*/
public void destroy() {
System.out.println("servlet is destroyed");
}
/**
* 配置
* @return
*/
public ServletConfig getServletConfig() {
return config;
}
/**
* 信息
* @return
*/
public String getServletInfo() {
return "copyright 2007-1010";
}
}
GenericServlet类
GenericServlet是个抽象类，实现了Servlet, ServletConfig, Serializable接口，能处理任何请求，支持任何协议。主要方法如下：
- public void init(ServletConfig config) 初始化
- public abstract void service(ServletRequest request, ServletResponse response) 接收请求，返回响应，每次请求都会调用1次
- public void destroy() 销毁，只会被web container调用1次
- public ServletConfig getServletConfig() Servlet配置
- public String getServletInfo() Servlet信息
- public void init() 无参初始化
- public ServletContext getServletContext() Servlet上下文
- public String getInitParameter(String name) 根据参数name返回value
- public Enumeration getInitParameterNames() web.xml所有参数
- public String getServletName() Servlet名称
- public void log(String msg) 记录Servlet日志
- public void log(String msg,Throwable t) 记录Servlet日志和异常堆栈
以下是代码示例：
import javax.servlet.GenericServlet;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
public class First extends GenericServlet {
public void service(ServletRequest req, ServletResponse res)
throws IOException, ServletException {
res.setContentType("text/html");
PrintWriter out = res.getWriter();
out.print("<html><body>");
out.print("<b>hello generic servlet</b>");
out.print("</body></html>");
}
}
HttpServlet类
HttpServlet继承了GenericServlet抽象类。主要方法如下：
-
public void service(ServletRequest req,ServletResponse res) dispatches the request to the protected service method by converting the request and response object into http type.（这里结合英文解释比较清楚，转换类型后，调用第2个service）
-
protected void service(HttpServletRequest req, HttpServletResponse res) receives the request from the service method, and dispatches the request to the doXXX() method depending on the incoming http request type.（这里结合英文解释比较清楚，根据不同method，调用doXXX()方法）
-
protected void doGet(HttpServletRequest req, HttpServletResponse res) 处理GET请求，web container调用
-
protected void doPost(HttpServletRequest req, HttpServletResponse res) 处理POST请求，web container调用
-
protected void doHead(HttpServletRequest req, HttpServletResponse res) 处理HEAD请求，web container调用
-
protected void doOptions(HttpServletRequest req, HttpServletResponse res) 处理OPTIONS请求，web container调用
-
protected void doPut(HttpServletRequest req, HttpServletResponse res) 处理PUT请求，web container调用
-
protected void doTrace(HttpServletRequest req, HttpServletResponse res) 处理TRACE请求，web container调用
-
protected void doDelete(HttpServletRequest req, HttpServletResponse res) 处理DELETE请求，web container调用
-
protected long getLastModified(HttpServletRequest req) 上次修改时间
如果想深入学习Servlet API，可以在Maven pom.xml引入servlet包依赖，External Libraries查看源码。
标签：JavaWeb,Servlet,void,javax,API,res,servlet,public From： https://www.cnblogs.com/df888/p/18301949参考资料：
https://www.javatpoint.com/servlet-api
https://www.javatpoint.com/Servlet-interface
https://www.javatpoint.com/GenericServlet-class
https://www.javatpoint.com/HttpServlet-class
ChatGPT