实例：现在jsp页面传递一个名为username的参数到action中
url: http://localhost:8080/StudentSystem/role_list.action username=1321312
一、通过get set方法获取
在对应的action类中定义同名变量,并生成set get方法，那么参数将会自动获取值
String username;
public String getUsername()
{
return username;
}
public void setUsername(String username)
{
this.username = username;
}
System.out.println(username);//结果为1321312
二、通过ServletActionContext获取//导入import org.apache.struts2.ServletActionContext;
HttpServletRequest reqeust= ServletActionContext.getRequest();
String username=reqeust.getParameter("username");//字符串
//url: http://localhost:8080/StudentSystem/role_list.action username=1321312&username=34343
String[] username=reqeust.getParameterValues("username");//字符串数组
System.out.println(username);//结果为1321312
System.out.println(username[0]);//结果为1321312
三、通过ActionContext获取//导入import com.opensymphony.xwork2.ActionContext;
ActionContext context = ActionContext.getContext();
Map params = context.getParameters();
String[] username=(String[])params.get("username");
//ActionContext获取到一个对象如object或String[]
System.out.println(username[0]);//结果为1321312