（22）增加表单
l 下面增加一个允许用户输入百分值的表单。由于表单中使用了Spring的标记，所以将dist/spring.tld导入到springapp/WEB-INF目录下，并在web.xml中增加<taglib>条目
<taglib>
<taglib-uri>/spring</taglib-uri>
<taglib-location>/WEB-INF/spring.tld</taglib-location>
</taglib>
l 在表单页面priceincrease.jsp中，定义了包含一个输入增加百分比的文本域和提交按钮的表单
<%@ include file="/WEB-INF/jsp/include.jsp" %>
<%@ taglib prefix="spring" uri="/spring" %>
<html>
<head><title><fmt:message key="title"/></title></head>
<body>
<h1><fmt:message key="priceincrease.heading"/></h1>
<form method="post">
<table width="95%" bgcolor="f8f8ff" border="0" cellspacing="0" cellpadding="5">
<tr>
<td alignment="right" width="20%">Increase (%):</td>
<spring:bind path="priceIncrease.percentage">
<td width="20%">
<input type="text" name="percentage" value="<c:out value="${status.value}"/>">
</td>
<td width="60%">
<font color="red"><c:out value="${status.errorMessage}"/></font>
</td>
</spring:bind>
</tr>
</table>
<br>
<spring:hasBindErrors name="priceIncrease">
<b>Please fix all errors!</b>
</spring:hasBindErrors>
<br><br>
<input type="submit" alignment="center" value="Execute">
</form>
<a href="<c:url value="hello.htm"/>">Home</a>
</body>
</html>
l <spring:bind>绑定文本域到Command对象（后面介绍）的属性（由path属性指定），status.value变量表示绑定属性的值，status.errorMessage变量表示验证错误时返回的错误信息
l <spring:hasBindErrors>绑定错误到指定对象（由name属性指定）
l Command对象是个简单的JavaBean，传递给验证器，如果验证通过，再传递给控制器
package bus;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
public class PriceIncrease {
/** Logger for this class and subclasses */
protected final Log logger = LogFactory.getLog(getClass());
private int percentage;
public void setPercentage(int I) {
percentage = I;
logger.info(“Percentage set to “ + I);
}
public int getPercentage() {
return percentage;
}
}
l 用户提交表单时，表单的数据由Spring设置到Command对象中，并调用验证器进行数据有效性验证
package bus;
import org.springframework.validation.Validator;
import org.springframework.validation.Errors;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
public class PriceIncreaseValidator implements Validator {
private int DEFAULT_MIN_PERCENTAGE = 0;
private int DEFAULT_MAX_PERCENTAGE = 50;
private int minPercentage = DEFAULT_MIN_PERCENTAGE;
private int maxPercentage = DEFAULT_MAX_PERCENTAGE;
/** Logger for this class and subclasses */
protected final Log logger = LogFactory.getLog(getClass());
public boolean supports(Class clazz) {
return clazz.equals(PriceIncrease.class);
}
public void validate(Object obj, Errors errors) {
PriceIncrease pi = (PriceIncrease) obj;
if (pi == null) {
errors.rejectValue("percentage", "error.not-specified", null, "Value required.");
}
else {
logger.info("Validating with " + pi + ": " + pi.getPercentage());
if (pi.getPercentage() > maxPercentage) {
errors.rejectValue("percentage", "error.too-high",
new Object[] {new Integer(maxPercentage)}, "Value too high.");
}
if (pi.getPercentage() <= minPercentage) {
errors.rejectValue("percentage", "error.too-low",
new Object[] {new Integer(minPercentage)}, "Value too low.");
}
}
}
public void setMinPercentage(int i) {
minPercentage = i;
}
public int getMinPercentage() {
return minPercentage;
}
public void setMaxPercentage(int i) {
maxPercentage = i;
}
public int getMaxPercentage() {
return maxPercentage;
}
}
l 验证器实现Validator接口，该接口有两个方法：
Ø supports()：决定指定类的对象是否能够验证
Ø validate()：实现验证对象，提供两个参数，一个是验证对象，一个是我们构建的包含与域属性相关的错误消息的Errors；错误消息可以使用前面介绍的status.errorMessage变量获取
l Errors对象的rejectValue()方法用来弹出验证对象指定域属性的指定错误描述，它包含四个参数：属性名，消息key值（消息在属性文件中定义），消息参数（提供动态消息）和缺省消息
