16.4 解耦控制器代码

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16.4 解耦控制器代码

app16a中的业务逻辑代码都写在了Servlet控制器中，这个Servlet类将随着应用复杂度的增加而不断膨胀。为避免此问题，我们应该将业务逻辑代码提取到独立的被称为controller的类中。
在app16b应用（app16a的升级版）中，controller目录下有两个controller类，分别是InputProductController和SaveProductController。app16b应用的目录结构如下所示：
这里有一张图
这两个controller都实现了Controller接口（见清单16.6）。Controller接口只有handleRequest一个方法。Controller接口的实现类通过该方法访问到当前请求的HttpServletRequest和HttpServletResponse对象。

Controller接口

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package app16b.controller;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public interface Controller
{
    String handleRequest(HttpServletRequest request,
        HttpServletResponse response);
}

InputProductController类直接返回了ProductForm.jsp的路径。
而SaveProductController类则会读取请求参数来构造一个ProductForm对象，之后用ProductForm对象来构造一个Product对象，并返回ProductDetail.jsp路径。

InputProductController类

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package app16b.controller;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class InputProductController implements Controller {
    @Override
    public String handleRequest(HttpServletRequest request,
            HttpServletResponse response) {
        return "/WEB-INF/jsp/ProductForm.jsp";
    }
}

SaveProductController类

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package app16b.controller;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import app16b.domain.Product;
import app16b.form.ProductForm;
public class SaveProductController
    implements
        Controller
{
    @Override
    public String handleRequest(HttpServletRequest request,
        HttpServletResponse response)
    {
        ProductForm productForm = new ProductForm();
        // populate form properties
        productForm.setName(
            request.getParameter("name"));
        productForm.setDescription(
            request.getParameter("description"));
        productForm.setPrice(request.getParameter("price"));
        // create model
        Product product = new Product();
        product.setName(productForm.getName());
        product.setDescription(productForm.getDescription());
        try {
            product.setPrice(Float.parseFloat(
                productForm.getPrice()));
        } catch (NumberFormatException e) {}
        // insert code to add product to the database
        request.setAttribute("product", product);
        return "/WEB-INF/jsp/ProductDetails.jsp";
    }
}

将业务逻辑代码迁移到controller类的好处很明显：ControllerServlet变得更加专注。现在作用更像一个dispatcher，而非一个controller，因此，我们将其改名为DispatcherServlet。DispatcherServlet类（见清单16.9）检查每个URI，创建相应的controller，并调用其handleRequest方法。

DispatcherServlet类

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package app16b.servlet;
import java.io.IOException;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import app16b.controller.InputProductController;
import app16b.controller.SaveProductController;
public class DispatcherServlet extends HttpServlet
{
    private static final long serialVersionUID = 748495L;
    @Override
    public void doGet(HttpServletRequest request,
        HttpServletResponse response)
        throws IOException,ServletException
    {
        process(request, response);
    }
    @Override
    public void doPost(HttpServletRequest request,
        HttpServletResponse response)
        throws IOException,ServletException
    {
        process(request, response);
    }
    private void process(HttpServletRequest request,
        HttpServletResponse response)
        throws IOException,ServletException
    {
        String uri = request.getRequestURI();
        /*
         * uri is in this form: /contextName/resourceName, 
         * for example: /app10a/product_input. 
         * However, in the event of a default context, the 
         * context name is empty, and uri has this form
         * /resourceName, e.g.: /product_input
         */
        int lastIndex = uri.lastIndexOf("/");
        String action = uri.substring(lastIndex + 1);
        String dispatchUrl = null;
        if(action.equals("product_input.action")) {
            InputProductController controller = new InputProductController();
            dispatchUrl = controller.handleRequest(request, response);
        } else if(action.equals("product_save.action")) {
            SaveProductController controller = new SaveProductController();
            dispatchUrl = controller.handleRequest(request, response);
        }
        if(dispatchUrl != null) {
            RequestDispatcher rd = request
                .getRequestDispatcher(dispatchUrl);
            rd.forward(request, response);
        }
    }
}

现在，可以在浏览器中输入如下URL测试应用了：
http://localhost:8080/app16b/product_input.action