ServletContext域对象

场景：假设某个web服务，有两个servlet分别是servlet1和servlet2，servlet1要传参数name=zhangsan传送给servlet2，传统方法如下：

servlet1端：用response.sendRedirect函数，形式如：response.sendRedirect("/Servlet2?name=zhangsan")。

servlet2端：String name = (String)request.getParameter("name");

但是如果我要传的参数是一个对象呢，例如一个student对象。这时候就需要引入域对象的概念了。

域对象：作用是用于保存数据，获取数据。可以在不同的动态资源之间共享数据。

那么，上边的场景，用域对象来解决，示意图如下：

ServletContext就是一个域对象，下边是域对象操作的函数：

　　保存数据：void setAttribute(java.lang.String name, java.lang.Object object)

　　获取数据： java.lang.Object getAttribute(java.lang.String name)

　　删除数据： void removeAttribute(java.lang.String name)

实例：

servlet1

public class servlet1 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        //1.得到域对象
        ServletContext context = this.getServletContext();

        //2.把数据保存到域对象中
        //context.setAttribute("name", "eric");
        context.setAttribute("student", new Student("jacky",20));
        System.out.println("保存成功");
    }

}

class Student{
    private String name;
    private int age;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public Student(String name, int age) {
        super();
        this.name = name;
        this.age = age;
    }
    @Override
    public String toString() {
        return "Student [age=" + age + ", name=" + name + "]";
    }
    

servlet2

public class servlet2 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        //1.得到域对象
        ServletContext context = this.getServletContext();

        //2.从域对象中取出数据
        //String name = (String)context.getAttribute("name");
        Student student = (Student)context.getAttribute("student");
        //System.out.println("name="+name);

        System.out.println(student);
    }

}