非严谨–Servlet学习总结
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- 什么是Servlet？干啥用的？
- Java Server Applet的简称，小服务程序
- 指Java编写的服务器端程序，具有独立平台和协议的特性
- 主要用于交互式浏览和生成数据、动态web内容
- 具体到语言层面指实现了Servlet接口的类，大多数情况下只用于拓展基于HTTP协议的web服务器（继承HttpServlet）
- Servlet的工作工程概述
- web容器（web服务器）接收用户端请求
- 请求发送到Servlet程序
- Servlet响应请求，生成响应内容发送给服务器
- 服务器将响应内容发送给客户端
- Servlet的声明周期
- 调用init方法初始化
- 调用service方法处理请求
- 调用destroy方法销毁
- GC回收
- Servlet接口源码浏览（忽略异常）
void init(ServletConfig var1);
void service(ServletRequest var1, ServletResponse var2);
void destroy();
ServletConfig getServletConfig();
String getServletInfo();
- GenericServlet源码浏览
public abstract class GenericServlet implements Servlet {
private transient ServletConfig config;
public void init(ServletConfig config) throws ServletException {
this.config = config;
this.init();
}
public void init() throws ServletException {
}
public abstract void service(ServletRequest var1, ServletResponse var2) throws ServletException, IOException;
public void destroy() {
}
public ServletConfig getServletConfig() {
return this.config;
}
public String getServletInfo() {
return "";
}
}
- HttpServlet源码浏览
public abstract class HttpServlet extends GenericServlet {
protected void service(HttpServletRequest req, HttpServletResponse resp) {
//决定调用doGet()、doPost()等某个方法
}
protected void doGet(HttpServletRequest req, HttpServletResponse resp){...}
protected void doPost(HttpServletRequest req, HttpServletResponse resp){...}
...
}
- Servlet在web.xml中的映射设置
<servlet>
<!--给该servlet程序起个霸气的名字-->
<servlet-name>hello</servlet-name>
<!--servlet程序的全类名-->
<servlet-class>com.calmjava.servlet.Servlet01</servlet-class>
</servlet>
<servlet-mapping>
<!--与上边起的名字相同-->
<servlet-name>hello</servlet-name>
<!--相对工程的浏览器访问URL-->
<url-pattern>/servlet01</url-pattern>
</servlet-mapping>
- 编写第一个Servlet程序Demo
public class Servlet01 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
resp.setContentType("text/html");
resp.setCharacterEncoding("utf8");
PrintWriter out = resp.getWriter();
out.write("调用了我的第一个Servlet程序的doGet方法！");
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
- ServletContext概述
- web容器在启动是为每个web程序创建一个ServletContext对象，代表当前web应用
- 一个web应用的所有Servlet共享ServletContext，可以进行通信
- ServletConfig对象中维护了ServletContext对象的引用
- Servlet的应用Demo
- 共享资源
public class Servlet01 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//设置name=calmjava键值对
ServletContext context = getServletContext();
context.setAttribute("name", "calmjava");
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
public class Servlet02 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//获取name的值输出到网页
ServletContext context = getServletContext();
resp.setContentType("text/html");
resp.setCharacterEncoding("utf8");
String name = (String)context.getAttribute("name");
resp.getWriter().print(name);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
-
- 请求转发（与重定向区别）
public class Servlet03 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
ServletContext context = getServletContext();
RequestDispatcher dispatcher = context.getRequestDispatcher("/servlet映射路径");
dispatcher.forward(req, resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
- 读取资源文件
public class Servlet05 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//注意路径使用了打包后的相对路径
InputStream is = getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties");
Properties prop = new Properties();
prop.load(is);
String username = prop.getProperty("username");
String password = prop.getProperty("password");
is.close();
resp.getWriter().write(username + ":" + password);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
- 关于请求与响应
- web服务器接收http请求，创建代表请求的HttpServletRequest对象和代表响应的HttpServletResponse对象
- HttpServletRequest对象用来获取请求信息，HttpServletResponse对象用来响应信息
- HttpServletResponse
- 写出数据
ServletOutputStream getOutputStream() throws IOException;
PrintWriter getWriter() throws IOException;
- 设置响应头
void setCharacterEncoding(String var1);
void setContentLength(int var1);
void setContentLengthLong(long var1);
void setContentType(String var1);
- 一些响应状态码
int SC_OK = 200;
int SC_BAD_REQUEST = 400;
int SC_NOT_FOUND = 404;
int SC_BAD_GATEWAY = 502;
- 一些应用
- 输出信息(简单，不做演示)
- 下载文件
public class FileServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
ServletContext context = getServletContext();
//获取文件的绝对路径(当前工程打包后路径+我们填写的字符串)
String path = context.getRealPath("WEB-INF/classes/1.png");
//获取文件名(精彩的实现方式)
String fileName = path.substring(path.lastIndexOf("\\")+1);
//设置响应头让浏览器下载文件
resp.setHeader("Content-Disposition","attachment;filename="+fileName);
//获取文件输入流并写出
InputStream is = new FileInputStream(path);
ServletOutputStream os = resp.getOutputStream();
int len;
byte[] buffer = new byte[1024];
while ((len = is.read(buffer)) != -1) {
os.write(buffer,0,len);
}
//关闭流
os.close();
is.close();
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
- 重定向
public class RedirectServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
/*
通过抓包可以看到：状态码设置302 响应头Location：/Web03_war/down
*/
resp.sendRedirect("/Web03_war/down");
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
