cookies
cookie被保存在客户端
每个cookie存储的信息量是有限制的。针对某个域名，浏览器保存的cookie数量也是有限的。
cookie通过http header传输
servlet开发者可以控制cookie的存活时间。
cookie有一个缺点，用户可以通过设置浏览器拒绝接受cookie。
与cookie有关的类为
javax.servlet.http.Cookie
以及HttpServletRequest 和 HttpServletResponse interfaces中的部分方法.
创建cookie
Cookie cookie = new Cookie(name, value);
设置存活时间
cookie.setMaxAge(int maxAge);
Cookie默认的maxAge值为-1。
如果maxAge为负数，则表示该Cookie仅在本浏览器窗口以及本窗口打开的子窗口内有效，关闭窗口后该Cookie即失效。maxAge为负数的Cookie，为临时性Cookie，不会被持久化，不会被写到Cookie文件中。Cookie信息保存在浏览器内存中，因此关闭浏览器该Cookie就消失了。
如果maxAge为0，则表示删除该Cookie。Cookie机制没有提供删除Cookie的方法，因此通过设置该Cookie即时失效实现删除Cookie的效果。失效的Cookie会被浏览器从Cookie文件或者内存中删除。
设置访问路径
cookie.setPath(String url);
默认只有设置该 cookie 的 URI 及其子路径可以访问客户端中存储的cookie。
例：
cookie设置在如下面servlet中：http://localhost:8080/JavaWeb/servlet/CookieDemo，并没有指定path，则
/JavaWeb/servlet 就是当前 Cookie 的 path 。 若访问的地址的 URI 包含着 cookie 的路径，即 URI.startWith(cookie 的路径 ), 为 true ，则服务器可访问存储在客户端的cookie。
例：
如果浏览器存的 cookie 的路径是 /JavaWeb，则
http://localhost:8080/JavaWeb/servlet/CookieDemo：可访问
http://localhost:8080/JavaWeb/CookieDemo：可访问
例：
如果浏览器存的 cookie 的路径是 /JavaWeb/servlet/，则
http://localhost:8080/JavaWeb/servlet/CookieDemo：可访问
http://localhost:8080/JavaWeb/CookieDemo：不可访问
如果一个 cookie 的路径设置成了 /JavaWeb ，意味着浏览器访问当前应用下的所有资源时都会带着该 cookie 给服务器。
设置domain
cookie.setDomain(String domain);
read cookie
例：读取一个名为maxRecords的cookie
Cookie[] cookies = request.getCookies();
Cookie maxRecordsCookie = null;
if (cookies != null) {
for (Cookie cookie : cookies) {
if (cookie.getName().equals("maxRecords")) {
maxRecordsCookie = cookie;
break;
}
}
}
delete cookie
例：删除一个名为userName的cookie
Cookie cookie = new Cookie("userName", "");
cookie.setMaxAge(0);
response.addCookie(cookie);
例 在PreferenceServlet中设置cookie
@WebServlet(name = "PreferenceServlet",
urlPatterns = { "/preference" })
public class PreferenceServlet extends HttpServlet {
private static final long serialVersionUID = 888L;
public static final String MENU =
"<div style='background:#e8e8e8;"
+ "padding:15px'>"
+ "<a href='cookieClass'>Cookie Class</a> "
+ "<a href='cookieInfo'>Cookie Info</a> "
+ "<a href='preference'>Preference</a>" + "</div>";
@Override
public void doGet(HttpServletRequest request,
HttpServletResponse response) throws ServletException,
IOException {
response.setContentType("text/html");
PrintWriter writer = response.getWriter();
writer.print("<!DOCTYPE html>"
+ "<html><head>" + "<title>Preference</title>"
+ "<style>table {" + "font-size:small;"
+ "background:NavajoWhite }</style>"
+ "</head><body>"
+ MENU
+ "Please select the values below:"
+ "<form method='post'>"
+ "<table>"
+ "<tr><td>Title Font Size: </td>"
+ "<td><select name='titleFontSize'>"
+ "<option>large</option>"
+ "<option>x-large</option>"
+ "<option>xx-large</option>"
+ "</select></td>"
+ "</tr>"
+ "<tr><td>Title Style & Weight: </td>"
+"<td><select name='titleStyleAndWeight' multiple>"
+ "<option>italic</option>"
+ "<option>bold</option>"
+ "</select></td>"
+ "</tr>"
+ "<tr><td>Max. Records in Table: </td>"
+ "<td><select name='maxRecords'>"
+ "<option>5</option>"
+ "<option>10</option>"
+ "</select></td>"
+ "</tr>"
+ "<tr><td rowspan='2'>"
+ "<input type='submit' value='Set'/></td>"
+ "</tr>"
+ "</table>" + "</form>" + "</body></html>");
}
@Override
public void doPost(HttpServletRequest request,
HttpServletResponse response) throws ServletException,
IOException {
String maxRecords = request.getParameter("maxRecords");
String[] titleStyleAndWeight = request
.getParameterValues("titleStyleAndWeight");
String titleFontSize =
request.getParameter("titleFontSize");
response.addCookie(new Cookie("maxRecords", maxRecords));
response.addCookie(new Cookie("titleFontSize",
titleFontSize));
// delete titleFontWeight and titleFontStyle cookies first
// Delete cookie by adding a cookie with the maxAge = 0;
Cookie cookie = new Cookie("titleFontWeight", "");
cookie.setMaxAge(0);
response.addCookie(cookie);
cookie = new Cookie("titleFontStyle", "");
cookie.setMaxAge(0);
response.addCookie(cookie);
if (titleStyleAndWeight != null) {
for (String style : titleStyleAndWeight) {
if (style.equals("bold")) {
response.addCookie(new
Cookie("titleFontWeight", "bold"));
} else if (style.equals("italic")) {
response.addCookie(new Cookie("titleFontStyle",
"italic"));
}
}
}
response.setContentType("text/html");
PrintWriter writer = response.getWriter();
writer.println("<!DOCTYPE html>"
+ "<html><head>" + "<title>Preference</title></head>"
+ "<body>" + MENU
+ "Your preference has been set."
+ "<br/><br/>Max. Records in Table: " + maxRecords
+ "<br/>Title Font Size: " + titleFontSize
+ "<br/>Title Font Style & Weight: ");
// titleStyleAndWeight will be null if none of the options
// was selected
if (titleStyleAndWeight != null) {
writer.println("<ul>");
for (String style : titleStyleAndWeight) {
writer.print("<li>" + style + "</li>");
}
writer.println("</ul>");
}
writer.println("</body></html>");
}
}
读取cookie：maxRecords
@WebServlet(name = "CookieClassServlet",
urlPatterns = { "/cookieClass" })
public class CookieClassServlet extends HttpServlet {
private static final long serialVersionUID = 837369L;
private String[] methods = {
"clone", "getComment", "getDomain",
"getMaxAge", "getName", "getPath",
"getSecure", "getValue", "getVersion",
"isHttpOnly", "setComment", "setDomain",
"setHttpOnly", "setMaxAge", "setPath",
"setSecure", "setValue", "setVersion"
};
@Override
public void doGet(HttpServletRequest request,
HttpServletResponse response) throws ServletException,
IOException {
Cookie[] cookies = request.getCookies();
Cookie maxRecordsCookie = null;
if (cookies != null) {
for (Cookie cookie : cookies) {
if (cookie.getName().equals("maxRecords")) {
maxRecordsCookie = cookie;
break;
}
}
}
int maxRecords = 5; // default
if (maxRecordsCookie != null) {
try {
maxRecords = Integer.parseInt(
maxRecordsCookie.getValue());
} catch (NumberFormatException e) {
// do nothing, use maxRecords default value
}
}
response.setContentType("text/html");
PrintWriter writer = response.getWriter();
writer.print("<!DOCTYPE html>"
+ "<html><head>" + "<title>Cookie Class</title></head>"
+ "<body>" + PreferenceServlet.MENU
+ "<div>Here are some of the methods in " +
"javax.servlet.http.Cookie");
writer.print("<ul>");
for (int i = 0; i < maxRecords; i++) {
writer.print("<li>" + methods[i] + "</li>");
}
writer.print("</ul>");
writer.print("</div></body></html>");
}
}
读取多个cookie用来控制css样式
@WebServlet(name = "CookieInfoServlet", urlPatterns = { "/cookieInfo" })
public class CookieInfoServlet extends HttpServlet {
private static final long serialVersionUID = 3829L;
@Override
public void doGet(HttpServletRequest request,
HttpServletResponse response) throws ServletException,
IOException {
Cookie[] cookies = request.getCookies();
StringBuilder styles = new StringBuilder();
styles.append(".title {");
if (cookies != null) {
for (Cookie cookie : cookies) {
String name = cookie.getName();
String value = cookie.getValue();
if (name.equals("titleFontSize")) {
styles.append("font-size:" + value + ";");
} else if (name.equals("titleFontWeight")) {
styles.append("font-weight:" + value + ";");
} else if (name.equals("titleFontStyle")) {
styles.append("font-style:" + value + ";");
}
}
}
styles.append("}");
response.setContentType("text/html");
PrintWriter writer = response.getWriter();
writer.print("<!DOCTYPE html>"
+ "<html><head>" + "<title>Cookie Info</title>"
+ "<style>" + styles.toString() + "</style>"
+ "</head><body>" + PreferenceServlet.MENU
+ "<div class='title'>"
+ "Session Management with Cookies:</div>");
writer.print("<div>");
// cookies will be null if there's no cookie
if (cookies == null) {
writer.print("No cookie in this HTTP response.");
} else {
writer.println("<br/>Cookies in this HTTP response:");
for (Cookie cookie : cookies) {
writer.println("<br/>" + cookie.getName() + ":"
+ cookie.getValue());
}
}
writer.print("</div>");
writer.print("</body></html>");
}
}