場景：假設某個web服務，有兩個servlet分別是servlet1和servlet2，servlet1要傳參數name=zhangsan傳送給servlet2，傳統方法如下：

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

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

但是如果我要傳的參數是一個對象呢，例如一個student對象。這時候就需要引入域對象的概念了。

域對象：作用是用於保存數據，獲取數據。可以在不同的動態資源之間共享數據。

那麽，上邊的場景，用域對象來解決，示意圖如下：

ServletContext就是一個域對象，下邊是域對象操作的函數：

　　保存數據：void setAttribute(java.lang.String name, java.lang.Object object)

　　獲取數據： java.lang.Object getAttribute(java.lang.String name)

　　刪除數據： void removeAttribute(java.lang.String name)

實例：

servlet1

public class servlet1 extends HttpServlet {

    
 
public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        //1.得到域對象
        ServletContext context = this.getServletContext();
        
        //2.把數據保存到域對象中
        //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.得到域對象
        ServletContext context = this.getServletContext();
        
        //2.從域對象中取出數據
        //String name = (String)context.getAttribute("name");
        Student student = (Student)context.getAttribute("student");
        //System.out.println("name="+name);
        
        System.out.println(student);
    }

}

ServletContext域對象