Head First Servlet and JSP 笔记 Servlet 部分

第四章

1、Servlet继承树

2、LifeCycle

   1 init()  2 service() 3 doGet() or doPost()

3、request

You can have multiple values for a single parameter! That means you’ll need getParameterValues() that returns an array, instead of getParameter() that returns a String. 

4、getServerPort(), getLocalPort(), and getRemotePort() 

getServerPort() says, “to which port was the request originally SENT?” while getLocalPort() says, “on which port did the request END UP?” Yes, there’s a difference, because although the requests are sent to a single port (where the server is listening), the server turns around and finds a different local port for each thread so that the app can handle multiple clients at the same time. 

5、ServletRequest interface

 

6、Servlet Response Interface

7、download a JAR file by servlet

public class CodeReturn extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException
 {
response.setContentType(“application/jar”);
ServletContext ctx = getServletContext();;
InputStream is = ctx.getResourceAsStream(“/bookCode.jar”);int read = 0;;
byte[] bytes = new byte[1024];;
OutputStream os = response.getOutputStream();
 while ((read = is.read(bytes)) != -1) 
{
os.write(bytes, 0, read); 
}
os.flush();
os.close();
}
}

8、

Common MIME types:

text/html
application/pdf

video/quicktime

application/java

image/jpeg

application/jar

application/octet-stream

application/x-zip 

9、

To make sure everything works correctly, your best practice (and in some cases a

requirement) is to always call setContentType() first, BEFORE you call the method that gives you your output stream (getWriter() or getOutputStream()). That’ll guarantee you won’t run into conflicts between the content type and the output stream. 

10、

You’ve got two choices for output:

characters or bytes 

ServletOutputStream for bytes, or a PrintWriter for character data. 

PrintWriter writer = response.getWriter();;
writer.println(“some text and HTML”);;

ServletOutputStream out = response.getOutputStream();;;;
out.write(aByteArray);;

11、redirect

if (worksForMe) {
// handle the request
} else { response.sendRedirect(“http://www.oreilly.com”);;
}

相对寻址

sendRedirect(“foo/stuff.html”);

绝对寻址（webroot）

sendRedirect(“/foo/stuff.html”);

第五章 attributes and listeners

1、servlet param

<servlet>
  <servlet-name>BeerParamTests</servlet-name> 
  <servlet-class>TestInitParams</servlet-class>

  <init-param>
    <param-name>adminEmail</param-name> 
    <param-value>likewecare@wickedlysmart.com</param-value>
  </init-param>
</servlet>

out.println(getServletConfig().getInitParameter(“adminEmail”));;

You can’t use servlet init parameters until the servlet is initialized 

e.g.

<?xml version=”1.0” encoding=”ISO-8859-1”?> <web-app xmlns=”http://java.sun.com/xml/ns/j2ee”
xmlns:xsi=”http://www.w3.org/2001/XMLSchema-instance” xsi:schemaLocation=”http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd” version=”2.4”>

<servlet>
  <servlet-name>BeerParamTests</servlet-name> 
  <servlet-class>com.example.TestInitParams</servlet-class>
  <init-param>
    <param-name>adminEmail</param-name>
    <param-value>likewecare@wickedlysmart.com</param-value>
  </init-param> 
  <init-param>
    <param-name>mainEmail</param-name>
    <param-value>blooper@wickedlysmart.com</param-value>
   </init-param>
</servlet>

<servlet-mapping>
  <servlet-name>BeerParamTests</servlet-name>
  <url-pattern>/Tester.do</url-pattern>
</servlet-mapping>


</web-app>

2、Context init parameter

<servlet> 
    <servlet-name>BeerParamTests</servlet-name> 
    <servlet-class>TestInitParams</servlet-class>
</servlet>

<context-param>
    <param-name>adminEmail</param-name>
    <param-value>clientheaderror@wickedlysmart.com</param-value>
</context-param>

out.println(getServletContext().getInitParameter(“adminEmail”));;



ServletContext context = getServletContext();
out.println(context.getInitParameter(“adminEmail”));

diff:

ServletConfig is one per servlet ServletContext is one per web app 

If the app is distributed, there’s one ServletContext per JVM! 

getServletConfig().getServletContext().getInitParameter()

this.getServletContext().getInitParameter()

3、listener

package com.example;
 import javax.servlet.*;
public class MyServletContextListener implements ServletContextListener 
{
  public void contextInitialized(ServletContextEvent event) 
  {
    ServletContext sc = event.getServletContext();
    String dogBreed = sc.getInitParameter(“breed”);
    Dog d = new Dog(dogBreed);;
    sc.setAttribute(“dog”, d);
  }

    public void contextDestroyed(ServletContextEvent event)
    { // nothing to do here
    }
 }

<web-app xmlns=”http://java.sun.com/xml/ns/j2ee” xmlns:xsi=”http://www.w3.org/2001/XMLSchema-instance” xsi:schemaLocation=”http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd” version=”2.4”>

<servlet>
  <servlet-name>ListenerTester</servlet-name> 
  <servlet-class>com.example.ListenerTester</servlet-class>
</servlet>

<servlet-mapping> 
  <servlet-name>ListenerTester</servlet-name>
  <url-pattern>/ListenTest.do</url-pattern>
</servlet-mapping>

<context-param> 
  <param-name>breed</param-name> 
  <param-value>Great Dane</param-value>
</context-param>

<listener>
  <listener-class>com.example.MyServletContextListener </listener-class>
</listener>

</web-app>

8种listener

4、

Context scope isn’t thread-safe! 

public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException 
{
response.setContentType(“text/html”);
PrintWriter out = response.getWriter();
out.println(“test context attributes<br>”);
synchronized(getServletContext()) 
{
  getServletContext().setAttribute(“foo”, “22”);
  getServletContext().setAttribute(“bar”, “42”);
  out.println(getServletContext().getAttribute(“foo”));
  out.println(getServletContext().getAttribute(“bar”));
}
}

Protect session attributes by

synchronizing on the HttpSession 

public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException
{
response.setContentType(“text/html”);
PrintWriter out = response.getWriter();
out.println(“test session attributes<br>”);
HttpSession session = request.getSession();
synchronized(session) 
{
session.setAttribute(“foo”, “22”);; session.setAttribute(“bar”, “42”);
out.println(session.getAttribute(“foo”));
out.println(session.getAttribute(“bar”));
}
}

5、RequestDispatcher

Getting a RequestDispatcher from a ServletRequest 

RequestDispatcher view = request.getRequestDispatcher(“result.jsp”);;

Getting a RequestDispatcher from a ServletContext 

RequestDispatcher view = getServletContext().getRequestDispatcher(“/result.jsp”);;

Calling forward() on a RequestDispatcher 

view.forward(request, response);;

You can’t forward the request if you’ve already committed a response

第六章 Session

1、

So there’s an overloaded getSession(boolean) method just for that purpose. If you don’t want to create a new session, call getSession(false), and you’ll get either null, or a pre-existing HttpSession. 

2、

If cookies aren’t enabled, it means the client
will never join the session. In other words, the session’s isNew() method will always return true. 

3、

A client with cookies disabled will ignore “Set-Cookie” response headers 

4、URL rewrite

If cookies don’t work, the Container falls back to URL rewriting, but only
if you’ve done the extra work of encoding all the URLs you send in the response. I 

 If you do encode your URLs, the Container will first attempt to use cookies for session management, and fall back to URL rewriting only if the cookie approach fails. 

out.println(“<a href=\”” + response.encodeURL(“/BeerTest.do”) + “\”>click me</a>”);;

response.encodeRedirectURL(“/BeerTest.do”)

5、session timeout

Configuring a timeout in the DD has virtually the same effect as calling setMaxInactiveInterval() on every session that’s created. 

<web-app ...>
 <servlet>... </servlet>
<session-config>
<session-timeout>15</session-timeout>
</session-config>
</web-app>

Timeouts in the DD are in MINUTES! 

session.setMaxInactiveInterval(20*60);

The argument to the method is in seconds,

 

6、Cookie

Creating a new Cookie 

Cookie cookie = new Cookie(“username”, name);

Setting how long a cookie will live on the client 

cookie.setMaxAge(30*60);;

setMaxAge is defined in SECONDS. This code says “stay alive on the client for 30*60 seconds” (30 minutes). Setting max age to -1 makes the cookie disappear when the browser exits.  

Sending the cookie to the client 

response.addCookie(cookie);;

Getting the cookie(s) from the client request 

Cookie[] cookies = request.getCookies();; for (int i = 0;; i < cookies.length;; i++) {
Cookie cookie = cookies[i];;
if (cookie.getName().equals(“username”)) {
String userName = cookie.getValue();; out.println(“Hello “ + userName);; break;;
} }

There’s no getCookie(String) method... you can only get cookies in a Cookie array, and then you have to loop over the array to find the one you want. 

7、Session related listener

暂时省略