Java 如何从一个 servlet 文件调用另一个 servlet 文件？
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How can i call from one servlet file to another servlet file?
提问by selvam
I am using net beans 7.1 and i create one JSP file with two servlet files. like
我使用的是 net beans 7.1，我创建了一个带有两个 servlet 文件的 JSP 文件。喜欢
index.jsp --->servlet1.java --->servlet2.java
index.jsp --->servlet1.java --->servlet2.java
I give some value from index.jspfile and send to servlet1.java.
我从index.jsp文件中给出一些价值并发送到servlet1.java.
In this servlet1.javafile I call servlet2.javafile.
在这个servlet1.java文件中，我将servlet2.javafile.
Then it throws NullPointerException.
How can I solve this?
然后它抛出NullPointerException。
我该如何解决这个问题？
My code like this.
我的代码是这样的。
index.jsp
索引.jsp
<form action="servlet1" method="post">
servlet1.java
servlet1.java
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
..................
..................
..................
servlet2 ob=new servlet2();
ob.doPost(request, response);
..................
..................
..................
}
Then it throws NullPointerException.
然后它抛出NullPointerException。
采纳答案by Aniket Kulkarni
RequestDispatcher rd = request.getRequestDispatcher("servlet2");
rd.forward(request,response);
RequestDispatcher
请求调度器
Defines an object that receives requests from the client and sends them to any resource (such as a servlet, HTML file, or JSP file) on the server.
定义一个对象，该对象接收来自客户端的请求并将它们发送到服务器上的任何资源（例如 servlet、HTML 文件或 JSP 文件）。
Update
更新
No need to create an object of servlet manually, just simply use RequestDispatcherto call servlet because web container controls the lifecycleof servlet.
不需要手动创建servlet对象，直接RequestDispatcher调用servlet即可，因为web容器控制 servlet的生命周期。
From Oracle JavaEE docs Servlet Lifecycle
来自 Oracle JavaEE 文档Servlet 生命周期
The lifecycle of a servlet is controlled by the container in which the servlet has been deployed.
When a request is mapped to a servlet, the container performs the following steps.
servlet 的生命周期由部署 servlet 的容器控制。
当请求映射到 servlet 时，容器执行以下步骤。
If an instance of the servlet does not exist, the web container
Loads the servlet class.
Creates an instance of the servlet class.
Initializes the servlet instance by calling the init method. Initialization is covered in Creating and Initializing a Servlet.
Invokes the service method, passing request and response objects. Service methods are discussed in Writing Service Methods.
如果 servlet 的实例不存在，则 Web 容器
加载 servlet 类。
创建 servlet 类的实例。
通过调用 init 方法初始化 servlet 实例。创建和初始化 Servlet 中介绍了初始化。
调用服务方法，传递请求和响应对象。服务方法在编写服务方法中讨论。
回答by Santhosh
What are you trying here,
你在这里尝试什么，
servlet2 ob=new servlet2();
ob.doPost(request, response);
Its not necessary to create an object explicitly for a servlet, Web container creates an instance for a servlet and shares it during the app's lifetime. Though you have created an object here, it will return the existing object only.
不必为 servlet 显式创建对象，Web 容器会为 servlet 创建实例并在应用程序的生命周期内共享它。尽管您在此处创建了一个对象，但它只会返回现有对象。
You can is instead go for Request Dispatcher or page Redirect.
您可以改为使用Request Dispatcher 或 page Redirect。
