Cookie:
一、Cookie的概念
1.服務器可以向客戶端寫內容2.只能是文本內容
3.客戶端可以阻止服務器寫入
4.只能拿自己WebApp寫入的內容
5.Cookie分爲兩種:a.屬於窗口/子窗口的;b.屬於文本的。
6.一個servlet/jsp設置的cookie能夠被同一路徑下面或者子路徑下面的servlet/jsp讀到(路徑=URL)(路徑 !=真實文件路徑)
二、創建Cookie的示例代碼
創建cookie的代碼:cookie = new Cookie("cookie_name","cookie_value");
cookie.setMaxAge(3600);//不設置的話,cookie寫在內存裏,窗口關閉,該cookie就失效了。
resp.addCookie(cookie);
拿到cookie的代碼:
Cookie[] cookies = req.getCookies();
cookies[0].getName();
cookies[0].getValue();
三、Cookie路徑試驗
<url-pattern>/servlet/TestCookies</url-pattern> //設置cookie<url-pattern>/servlet/ShowCookies</url-pattern> //拿cookie,可以拿到
<url-pattern>/TestCookies</url-pattern> //設置cookie
<url-pattern>/servlet/ShowCookies</url-pattern> //拿cookie,可以拿到
<url-pattern>/servlet/TestCookies</url-pattern> //設置cookie
<url-pattern>/ShowCookies</url-pattern> //拿cookie,不可以拿到
Session:
一、Session的概念和規則
Session是記錄在服務器端的,並且把session-id寫在臨時cookie中。在某段時間一連串客戶端與服務器端的“交易”
在jsp/servlet中如果瀏覽器不支持cookie,可以通過URL重寫來實現,就是將一些額外數據追加到表示會話的每個URL末尾,服務器在該標示符與其存儲的有關的該會話的數據之間建立關聯。
可以通過程序來終止一個會話。如果客戶端在一定時間內沒有操作,服務器會自動終止會話。
通過HttpSession來讀寫Session(地址欄傳送Session)
規則:
如果瀏覽器支持Cookie,創建Session的時候把SessionID保存在Cookie裏
如果不支持,必須自己編程使用URL重寫的方式實現Session
response.encodeURL()
轉碼
URL後面加入SessionID
Session不像Cookie擁有路徑訪問的問題
同一個application下的servlet/jsp可以共享同一個session,前提是同一個客戶端窗口。
二、Session使用演示
Session的信息:
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Date;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
public class SessionInfo extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
HttpSession mysession = req.getSession(true);
resp.setContentType("text/html");
PrintWriter pw = resp.getWriter();
pw.print("<html><head>");
pw.print("<title>Session Info</title>");
pw.print("</head><body>");
pw.print("<h2>Session Information</h2>");
pw.print("New Session: " + mysession.isNew());
pw.print("<br />SessionID:" + mysession.getId());
pw.print("<br />Session created time:" + new Date(mysession.getCreationTime()));
pw.print("<br />Session last access time:" + new Date(mysession.getLastAccessedTime()));
pw.print("<h2>Request Information</h2>");
pw.print("<br />SessionID from request:" + req.getRequestedSessionId());
pw.print("<br />SessionID via cookie:" + req.isRequestedSessionIdFromCookie());
pw.print("<br /> SessionID via rewrite URL" + req.isRequestedSessionIdFromURL());
pw.print("<br /> Valid Session" + req.isRequestedSessionIdValid());
pw.print("<br /> <a href = 'SessionInfo'>refresh</a>");
// 重寫url
pw.print("<br /> <a href =" + resp.encodeURL("SessionInfo") +">refresh</a>");
pw.print("</body></html>");
}
}
三、Session示例代碼解析
tomcat中的通用session過期時間設置爲:conf-->web.xml裏面的<session-config>裏面的<session-timeout>(時間單位爲分鐘)。
<session-config>
<session-timeout>30</session-timeout>
</session-config>
四、Session的作用及示例
作用:session裏面可以存任何你想要存放的內容,使用setAttribute(String name,Object value)設置session裏的內容,用getAttribute(String name)獲取Session裏的內容
示例代碼:
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
public class ShowSession extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
HttpSession session = req.getSession(true);
String head;
resp.setContentType("text/html");
PrintWriter pw = resp.getWriter();
Integer count = (Integer) session.getAttribute("access");
if(count == null) {
count = new Integer(0);
head = "hi,newcommer!";
}else {
count = new Integer(count.intValue() + 1);
head = "welcome back";
}
session.setAttribute("access", count);
pw.print("<html><body><h2>"+ head +"</h2>" +
count +
"</body></html>");
}
}
五、Session總結
1.服務器的一塊內存(存key-value)2.和客戶端窗口對應(子窗口)(獨一無二)
3.客戶端和服務器有對應的SessionID
4.客戶端向服務器端發送SessionID的時候兩種方式:
cookie(內存cookie)
rewriten URL
5.瀏覽器禁掉cookie,就不能使用session(使用cookie實現的session)
6.如果想安全的使用session(不論客戶端是否禁止cookie),只能使用URL重寫(大大增加編程負擔),所以很多網站要求客戶端打開cookie
application:
用於保存整個WebApplication的聲明週期內都可以訪問的數據
在API中表現爲ServletContext
通過HttpServlet的getServletContext方法可以拿到
通過ServletContext的get/setAttribute方法取得和設置(用法跟session有點類似)
用法示例:
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class TestServletContext extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
ServletContext context = req.getServletContext();
resp.setContentType("text/html");
PrintWriter pw = resp.getWriter();
Integer count = (Integer) context.getAttribute("access");
if(count == null) {
count = new Integer(0);
}else {
count = new Integer(count.intValue() + 1);
}
context.setAttribute("access", count);
pw.print("<html><body>" +
count +
"</body></html>");
}
}
數據庫處理_1:
1.JavaBean 的概念
廣義的bean:普通的java類; 狹義的bean:符合sun JavaBean標準的類:屬性私有,首字母小寫,具有getters和setters,具有一個參數爲空的構造方法,具有GUI表現,必須放在包裏面(不能使用裸體類),用來實現某一業務邏輯或者取得特定結果。
使用bean連接數據庫代碼示例:
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.*;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class ShowRs extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
Connection conn = null;
Statement stmt = null;
ResultSet rs = null;
resp.setContentType("text/html");
PrintWriter pw = resp.getWriter();
pw.print("<head><title>顯示數據</title></head><body>" +
"<table border='1' cellspacing='6'><tr><td>ID</td>" +
"<td>title</td></tr>");
try {
Class.forName("com.mysql.jdbc.Driver");
conn = DriverManager.getConnection("jdbc:mysql://localhost/bbs?user=root&password=root");
stmt = conn.createStatement();
rs = stmt.executeQuery("select * from article");
while(rs.next()) {
pw.print("<tr><td>"+ rs.getInt(1)+"</td><td>"+ rs.getString("title")+"</td></tr>");
}
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
} finally {
if(rs != null) {
try {
rs.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
rs = null;
}
if(stmt != null) {
try {
stmt.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
stmt = null;
}
if(conn != null) {
try {
conn.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
conn = null;
}
}
pw.print("</table></body></html>");
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
}
}
使用bean連接數據庫代碼示例:
import java.sql.*;
public class DB {
static Connection conn = null;
public static Connection getConnection() {
try {
Class.forName("com.mysql.jdbc.Driver");
conn = DriverManager.getConnection("jdbc:mysql://localhost/bbs?user=root&password=root");
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
}
return conn;
}
public static Statement getStatement(Connection conn) {
Statement stmt = null;
try {
if(conn != null)
stmt = conn.createStatement();
} catch (SQLException e) {
e.printStackTrace();
}
return stmt;
}
public static ResultSet getResultSet(Statement stmt,String sql) {
ResultSet rs = null;
try {
if(stmt != null)
rs = stmt.executeQuery(sql);
} catch (SQLException e) {
e.printStackTrace();
}
return rs;
}
public static void colseConnection(Connection conn) {
if(conn != null) {
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
conn = null;
}
}
public static void closeStatement(Statement stmt) {
if (stmt != null) {
try {
stmt.close();
} catch (SQLException e) {
e.printStackTrace();
}
stmt = null;
}
}
public static void closeRS(ResultSet rs) {
if(rs != null) {
try {
rs.close();
} catch (SQLException e) {
e.printStackTrace();
}
rs = null;
}
}
}
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.*;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class ShowRsUseBean extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
resp.setContentType("text/html");
PrintWriter pw = resp.getWriter();
pw.print("<head><title>顯示數據</title></head><body>" +
"<table border='1' cellspacing='6'><tr><td>ID</td>" +
"<td>title</td></tr>");
Connection conn = DB.getConnection();
Statement stmt = DB.getStatement(conn);
ResultSet rs = DB.getResultSet(stmt, "select * from article");
try {
while (rs.next()) {
pw.print("<tr><td>"+ rs.getInt(1)+"</td><td>"+ rs.getString("title")+"</td></tr>");
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
DB.closeRS(rs);
DB.closeStatement(stmt);
DB.colseConnection(conn);
}
pw.print("</table></body></html>");
}
}