2.2 隐藏域
使用隐藏域来保持状态类似于URL重写技术，但不是将值附加到URL上，而是放到HTML表单的隐藏域中。当表单提交时，隐藏域的值也同时提交到服务器端。隐藏域技术仅当网页有表单时有效。该技术相对于 URL重写的优势在于：没有字符数限制，同时无须额外的编码。但该技术同URL重写一样，不适合跨越多个界面。
清单2.3展示了如何通过隐藏域来更新客户信息。清单2.2的Customer类为客户对象模型。
清单2.2 Customer类
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| package app02a.hiddenfields;
public class Customer
{
private int id;
private String name;
private String city;
public int getId()
{
return id;
}
public void setId(int id)
{
this.id = id;
}
public String getName()
{
return name;
}
public void setName(String name)
{
this.name = name;
}
public String getCity()
{
return city;
}
public void setCity(String city)
{
this.city = city;
}
}
|
清单2.3 CustomerServlet类
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| package app02a.hiddenfields;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@WebServlet(
name = "CustomerServlet",
urlPatterns =
{"/customer", "/editCustomer", "/updateCustomer"}
)
public class CustomerServlet extends HttpServlet
{
private static final long serialVersionUID = -20L;
private List<Customer> customers = new ArrayList<Customer>();
@Override
public void init() throws ServletException
{
Customer customer1 = new Customer();
customer1.setId(1);
customer1.setName("Donald D.");
customer1.setCity("Miami");
customers.add(customer1);
Customer customer2 = new Customer();
customer2.setId(2);
customer2.setName("Mickey M.");
customer2.setCity("Orlando");
customers.add(customer2);
}
private void sendCustomerList(HttpServletResponse response)
throws IOException
{
response.setContentType("text/html");
PrintWriter writer = response.getWriter();
writer.println("<html><head><title>Customers</title></head>"
+ "<body><h2>Customers </h2>");
writer.println("<ul>");
for (Customer customer : customers) {
writer.println("<li>" + customer.getName() + "("
+ customer.getCity() + ") (" + "<a href='editCustomer?id="
+ customer.getId() + "'>edit</a>)");
}
writer.println("</ul>");
writer.println("</body></html>");
}
private Customer getCustomer(int customerId)
{
for (Customer customer : customers) {
if (customer.getId() == customerId) {
return customer;
}
}
return null;
}
private void sendEditCustomerForm(HttpServletRequest request,
HttpServletResponse response) throws IOException
{
response.setContentType("text/html");
PrintWriter writer = response.getWriter();
int customerId = 0;
try {
customerId = Integer.parseInt(request.getParameter("id"));
} catch (NumberFormatException e) {}
Customer customer = getCustomer(customerId);
if (customer != null) {
writer
.println("<html><head>" + "<title>Edit Customer</title></head>"
+ "<body><h2>Edit Customer</h2>" + "<form method='post' "
+ "action='updateCustomer'>");
writer.println(
"<input type='hidden' name='id' value='" + customerId + "'/>");
writer.println("<table>");
writer
.println("<tr><td>Name:</td><td>" + "<input name='name' value='"
+ customer.getName().replaceAll("'", "'")
+ "'/></td></tr>");
writer
.println("<tr><td>City:</td><td>" + "<input name='city' value='"
+ customer.getCity().replaceAll("'", "'")
+ "'/></td></tr>");
writer.println("<tr>" + "<td colspan='2' style='text-align:right'>"
+ "<input type='submit' value='Update'/></td>" + "</tr>");
writer.println("<tr><td colspan='2'>"
+ "<a href='customer'>Customer List</a>" + "</td></tr>");
writer.println("</table>");
writer.println("</form></body>");
} else {
writer.println("No customer found");
}
}
@Override
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
{
String uri = request.getRequestURI();
if (uri.endsWith("/customer")) {
sendCustomerList(response);
} else if (uri.endsWith("/editCustomer")) {
sendEditCustomerForm(request, response);
}
}
@Override
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
{
int customerId = 0;
try {
customerId = Integer.parseInt(request.getParameter("id"));
} catch (NumberFormatException e) {}
Customer customer = getCustomer(customerId);
if (customer != null) {
customer.setName(request.getParameter("name"));
customer.setCity(request.getParameter("city"));
}
sendCustomerList(response);
}
}
|
CustomerServlet类继承自HttpServlet，其URL映射分别为/customer、/editCustomer和 /updateCustomer。前两个URL会调用Servlet的doGet方法， 而/updateCustomer 会调用doPost方法。
/customer是本例的入口URL。该URL会列举出在 init 方法中所初始化的类级别的列表对象customers（在 真实应用中，通常是从数据库中获取用户信息），如图下图所示。
![这里有一张图片]()
如图上图所示，每个客户信息后都有一个edit链接， 每个edit链接的href属性为 /editCustomer?id=customerId。当通过/editCustomer访问servlet时， servlet会返回一个编辑表单，如下图所示。
![这里有一张图片]()
此时,servlet返回的表单如下:
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| <form method="post" action="updateCustomer">
<input type="hidden" name="id" value="1">
<table>
<tbody>
<tr>
<td>Name:</td>
<td>
<input name="name" value="Donald D.">
</td>
</tr>
<tr>
<td>City:</td>
<td>
<input name="city" value="Miami">
</td>
</tr>
<tr>
<td colspan="2" style="text-align:right">
<input type="submit" value="Update">
</td>
</tr>
<tr>
<td colspan="2">
<a href="customer">Customer List</a>
</td>
</tr>
</tbody>
</table>
</form>
|
可以看到表达中的隐藏域为<input type="hidden" name="id" value="1">.
该隐藏域保存了所编辑的客户id，因为隐藏域包含在表单中,所以会随着表单一起提交给服务器,这样服务端就知道应更新哪个客户信息。
需要强调的是，表单是通过post方式提交的，因此调用的是servlet的doPost方法。
