Spring MVC 填充和验证下拉列表示例

模型类
添加PropertyEditorSupport
查看更改以显示下拉框
下拉验证
测试下拉菜单

原文： https://howtodoinjava.com/spring-mvc/spring-mvc-populate-and-validate-dropdown-example/

如果您正在使用 Spring MVC 开发的任何面向客户的 Web 应用程序，那么您可能还需要在应用程序 UI 中的某个位置使用下拉框。本教程将帮助您显示预填充的下拉列表，然后验证用户在提交表单时是否选择了任何值。

这篇文章是我以前关于 spring mvc 验证（使用 JSR-303 注解 ）的继续。我将修改相同的源代码。

在此示例中，我将显示一个用于向系统中添加新员工的表单。该表格将有一个下拉列表，列出所有部门。应用程序用户必须在提交表单之前从下拉列表中选择一个值。

Spring MVC 下拉菜单示例 – 空白表单

Table of Contents
Model Classes
Adding PropertyEditorSupport
View layer changes for displaying Dropdown box
Dropdown validation changes
Test The Application

模型类

DepartmentVO.java

package com.howtodoinjava.demo.model;
public class DepartmentVO 
{
    public DepartmentVO(Integer id, String name) {
        super();
        this.id = id;
        this.name = name;
    }
    private Integer id;
    private String name;
    //Setters and Getters
    @Override
    public String toString() {
        return "DepartmentVO [id=" + id + ", name=" + name + "]";
    }
}

EmployeeVO.java

此类具有DepartmentVO的关联属性。

package com.howtodoinjava.demo.model;
import java.io.Serializable;
import javax.validation.constraints.NotNull;
import org.hibernate.validator.constraints.NotEmpty;
public class EmployeeVO implements Serializable 
{
    private static final long serialVersionUID = 1L;
    private Integer id;
    @NotEmpty
    private String firstName;
    private String lastName;
    private String email;
    @NotNull
    private DepartmentVO department;
    //Setters and Getters
    @Override
    public String toString() {
        return "EmployeeVO [id=" + id + ", firstName=" + firstName
                + ", lastName=" + lastName + ", email=" + email
                + ", department=" + department + "]";
    }
}

添加`PropertyEditorSupport`

我们不会在 UI 中将DepartmentVO显示为 java 对象，而是当用户提交绑定到Department字段的属性时，HTTP POST 中只会出现一个字符串值。我们需要某种机制将字符串值转换回DepartmentVO实例并注入EmployeeVO实例。

Spring 为此提供了PropertyEditorSupport类。

DepartmentEditor.java

package com.howtodoinjava.demo.convertor;
import java.beans.PropertyEditorSupport;
import com.howtodoinjava.demo.model.DepartmentVO;
public class DepartmentEditor extends PropertyEditorSupport 
{
    //This will be called when user HTTP Post to server a field bound to DepartmentVO
    @Override
    public void setAsText(String id) 
    {
        DepartmentVO d;
        switch(Integer.parseInt(id))
        {
            case 1: d = new DepartmentVO(1,  "Human Resource"); break;
            case 2: d = new DepartmentVO(2,  "Finance"); break;
            case 3: d = new DepartmentVO(3,  "Information Technology"); break;
            default: d = null;
        }
        this.setValue(d);
    }
}

可以，但是 spring 怎么会知道我们有此类用于转换目的。为此，我们必须告诉 Spring。我们可以通过以下方式在控制器类中进行操作。

@InitBinder
public void initBinder(WebDataBinder binder) {
    binder.registerCustomEditor(DepartmentVO.class, new DepartmentEditor());
}

现在，每次将表单提交到EmployeeController且字段绑定到department的字段时，DepartmentEditor都会用于将字符串值转换为DepartmentVO实例。

EmployeeController的完整代码如下。

EmployeeController.java

package com.howtodoinjava.demo.controller;
import java.util.ArrayList;
import java.util.List;
import java.util.Set;
import javax.validation.ConstraintViolation;
import javax.validation.Validation;
import javax.validation.Validator;
import javax.validation.ValidatorFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.validation.BindingResult;
import org.springframework.validation.FieldError;
import org.springframework.web.bind.WebDataBinder;
import org.springframework.web.bind.annotation.InitBinder;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.SessionAttributes;
import org.springframework.web.bind.support.SessionStatus;
import com.howtodoinjava.demo.convertor.DepartmentEditor;
import com.howtodoinjava.demo.model.DepartmentVO;
import com.howtodoinjava.demo.model.EmployeeVO;
import com.howtodoinjava.demo.service.EmployeeManager;
@Controller
@RequestMapping("/employee-module/addNew")
@SessionAttributes("employee")
public class EmployeeController
{
    @Autowired
    EmployeeManager manager;
    private Validator validator;
    public EmployeeController()
    {
        ValidatorFactory validatorFactory = Validation.buildDefaultValidatorFactory();
        validator = validatorFactory.getValidator();
    }
    @InitBinder
    public void initBinder(WebDataBinder binder) {
        binder.registerCustomEditor(DepartmentVO.class, new DepartmentEditor());
    }
    @ModelAttribute("allDepartments")
    public List<DepartmentVO> populateDepartments() 
    {
        ArrayList<DepartmentVO> departments = new ArrayList<DepartmentVO>();
        departments.add(new DepartmentVO(-1,  "Select Department"));
        departments.add(new DepartmentVO(1,  "Human Resource"));
        departments.add(new DepartmentVO(2,  "Finance"));
        departments.add(new DepartmentVO(3,  "Information Technology"));
        return departments;
    }
    @RequestMapping(method = RequestMethod.GET)
    public String setupForm(Model model) {
        EmployeeVO employeeVO = new EmployeeVO();
        model.addAttribute("employee", employeeVO);
        return "addEmployee";
    }
    @RequestMapping(method = RequestMethod.POST)
    public String submitForm(@ModelAttribute("employee") EmployeeVO employeeVO,
            BindingResult result, SessionStatus status) {
        Set<ConstraintViolation<EmployeeVO>> violations = validator.validate(employeeVO);
        for (ConstraintViolation<EmployeeVO> violation : violations) 
        {
            String propertyPath = violation.getPropertyPath().toString();
            String message = violation.getMessage();
            // Add JSR-303 errors to BindingResult
            // This allows Spring to display them in view via a FieldError
            result.addError(new FieldError("employee", propertyPath, "Invalid "+ propertyPath + "(" + message + ")"));
        }
        if (result.hasErrors()) {
            return "addEmployee";
        }
        // Store the employee information in database
        // manager.createNewRecord(employeeVO);
        System.out.println(employeeVO);
        // Mark Session Complete
        status.setComplete();
        return "redirect:addNew/success";
    }
    @RequestMapping(value = "/success", method = RequestMethod.GET)
    public String success(Model model) {
        return "addSuccess";
    }
}

要了解有关此控制器中更多代码段的更多信息，请参考本 spring mvc 显示形式教程 。

查看更改以显示下拉框

要显示下拉列表，您必须将部门的集合提供给 jsp 文件。这是从控制器完成的。请注意，在此示例中，我对集合进行了硬编码。在生产类应用程序中，您将需要动态构建此集合。

@ModelAttribute("allDepartments")
public List<DepartmentVO> populateDepartments() 
{
    ArrayList<DepartmentVO> departments = new ArrayList<DepartmentVO>();
    departments.add(new DepartmentVO(-1,  "Select Department"));
    departments.add(new DepartmentVO(1,  "Human Resource"));
    departments.add(new DepartmentVO(2,  "Finance"));
    departments.add(new DepartmentVO(3,  "Information Technology"));
    return departments;
}

可以在form:select标记的 JSP 文件内部访问此allDepartments属性。

<%@ page contentType="text/html;charset=UTF-8"%>
<%@ taglib prefix="form" uri="http://www.springframework.org/tags/form"%>
<%@ taglib prefix="spring" uri="http://www.springframework.org/tags" %>
<html>
<head>
    <title>Add Employee Form</title>
    <style>
    .error 
    {
        color: #ff0000;
        font-weight: bold;
    }
    </style>
</head>
<body>
    <h2><spring:message code="lbl.page" text="Add New Employee" /></h2>
    <br/>
    <form:form method="post" modelAttribute="employee">
        <%-- <form:errors path="*" cssClass="error" /> --%>
        <table>
            <tr>
                <td><spring:message code="lbl.firstName" text="First Name" /></td>
                <td><form:input path="firstName" /></td>
                <td><form:errors path="firstName" cssClass="error" /></td>
            </tr>
            <tr>
                <td><spring:message code="lbl.lastName" text="Last Name" /></td>
                <td><form:input path="lastName" /></td>
                <td><form:errors path="lastName" cssClass="error" /></td>
            </tr>
            <tr>
                <td><spring:message code="lbl.email" text="Email Id" /></td>
                <td><form:input path="email" /></td>
                <td><form:errors path="email" cssClass="error" /></td>
            </tr>
            <!-- DROPDOWN code -->
            <tr>
                <td><spring:message code="lbl.department" text="Department" /></td>
                <td><form:select path="department" items="${allDepartments}" itemValue="id" itemLabel="name" /></td>
                <td><form:errors path="department" cssClass="error" /></td>
            </tr>
            <tr>
                <td colspan="3"><input type="submit" value="Add Employee"/></td>
            </tr>
        </table>
    </form:form>
</body>
</html>

下拉验证

为了验证下拉框，我们使用了以下内容。

1）我们在EmployeeVO内的部门字段中使用了@NotNull注解。如果字段为null，使用 JSR-303 的 spring 验证将自动引发错误。

@NotNull
private DepartmentVO department;

2）由于具有@NotNull注解，因此我们要做的就是在department字段中为所有意外值设置null。这是在DepartmentEditor内部完成的，因为在进入控制器代码之前，会调用DepartmentEditor.setAsText()来设置部门的正确值。

public void setAsText(String id) 
{
    DepartmentVO d;
    switch(Integer.parseInt(id))
    {
        case 1: d = new DepartmentVO(1,  "Human Resource"); break;
        case 2: d = new DepartmentVO(2,  "Finance"); break;
        case 3: d = new DepartmentVO(3,  "Information Technology"); break;
        default: d = null;
    }
    this.setValue(d);
}