[J2EE] Developing JavaServer Pages - How to Use the Methods of the Request Object
Developing JavaServer Pages - How to Use the Methods of the Request Object
كود:
getParameter(String param)
Returns the value of the specified parameter as a string if it exists or null if it doesn't. Often, this is the value defined in the Value attribute of the control in the HTML page or JSP.
كود:
getParameterValues(String param)
Returns an array of String objects containing all of the values that the given request parameter has or null if the parameter doesn't have any values.
Returns an Enumeration object that contains the names of all the parameters contained in the request. If the request has no parameters, the method returns an empty Enumeration object.
More Scriptlets
A scriptlet that determines if a checkbox is checked
كود:
<%
String rockCheckBox = request.getParameter("Rock");
// returns the value or "on" if checked, null otherwise.
if (rockCheckBox != null){
%>
You checked Rock music!
<%
}
%>
كود:
<%
String[] selectedCountries = request.getParameterValues("country");
// returns the values of items selected in list box.
for (int i = 0; i < selectedCountries.length; i++){
%>
<%= selectedCountries[i] %> <br>
<%
}
%>
كود:
<%
Enumeration parameterNames = request.getParameterNames();
while (parameterNames.hasMoreElements()){
String parameterName = (String) parameterNames.nextElement();
String parameterValue = request.getParameter(parameterName);
%>
<%= parameterName %> has value <%= parameterValue %>. <br>
<%
}
%>
You can use the getParameter method to return the value of the selected radio button in a group or the selected item in a combo box. You can also use it to return the value of a selected check box or independent radio button, but that value is null if it isn't selected.
If an independent radio button or a checkbox doesn't have a Value attribute, this method returns "on" if the control is selected or null if it isn't.
In most cases, the getParameter method returns the value of the parameter. For a textbox, that's usually the value entered by the user. But for a group of radio buttons or a combo box, that's the value of the button or item selected by the user.
For checkboxes or independent radio buttons that have a Value attribute, the getParameter method returns that value if the checkbox or button is selected and a null value if it isn't. For checkboxes or independent radio buttons that don't have a Value attribute, though, the getParameter method returns an "on" value if the checkbox or button is selected and a null value if it isn't. This is illustrated by the first example in this figure.
