学习SpringMVC——你们要的REST风格的CRUD来了

时间：2016-09-04 17:15:15 阅读：515 评论：0 收藏：0 [点我收藏+]

标签：

　　来来来，让一下，客官，您要的REST清蒸CRUD来了，火候刚刚好，不油不腻，请慢用~~~

　　如果说前面是准备调料，洗菜，切菜，摆盘，那么今天就来完整的上道菜，主要说的是基于REST风格实现数据的增删改查（CRUD）操作。

用料

　　entity：Employee + Department

　　对于这样的实体类大家肯定很熟悉，一个Employee就是一个员工，一个Department就是一个部门，一个员工只属于一个部门，一个部门可以对应多个员工。

　　Employee.java

package com.jackie.springmvc.crud.entities;

import java.util.Date;
import javax.validation.constraints.Past;
import org.hibernate.validator.constraints.Email;
import org.hibernate.validator.constraints.NotEmpty;
import org.springframework.format.annotation.DateTimeFormat;
import org.springframework.format.annotation.NumberFormat;

public class Employee {

	private Integer id;
	@NotEmpty
	private String lastName;

	@Email
	private String email;
	//1 male, 0 female
	private Integer gender;
	
	private Department department;
	
	@Past
	@DateTimeFormat(pattern="yyyy-MM-dd")
	private Date birth;
	
	@NumberFormat(pattern="#,###,###.#")
	private Float salary;

	public Integer getId() {
		return id;
	}

	public void setId(Integer id) {
		this.id = id;
	}

	public String getLastName() {
		return lastName;
	}

	public void setLastName(String lastName) {
		this.lastName = lastName;
	}

	public String getEmail() {
		return email;
	}

	public void setEmail(String email) {
		this.email = email;
	}

	public Integer getGender() {
		return gender;
	}

	public void setGender(Integer gender) {
		this.gender = gender;
	}

	public Department getDepartment() {
		return department;
	}

	public void setDepartment(Department department) {
		this.department = department;
	}

	public Date getBirth() {
		return birth;
	}

	public void setBirth(Date birth) {
		this.birth = birth;
	}

	public Float getSalary() {
		return salary;
	}

	public void setSalary(Float salary) {
		this.salary = salary;
	}

	@Override
	public String toString() {
		return "Employee [id=" + id + ", lastName=" + lastName + ", email="
				+ email + ", gender=" + gender + ", department=" + department
				+ ", birth=" + birth + ", salary=" + salary + "]";
	}

	public Employee(Integer id, String lastName, String email, Integer gender,
			Department department) {
		super();
		this.id = id;
		this.lastName = lastName;
		this.email = email;
		this.gender = gender;
		this.department = department;
	}

	public Employee() {
		// TODO Auto-generated constructor stub
	}
}

　　Department.java

package com.jackie.springmvc.crud.entities;

public class Department {

	private Integer id;
	private String departmentName;

	public Department() {
		// TODO Auto-generated constructor stub
	}
	
	public Department(int i, String string) {
		this.id = i;
		this.departmentName = string;
	}

	public Integer getId() {
		return id;
	}

	public void setId(Integer id) {
		this.id = id;
	}

	public String getDepartmentName() {
		return departmentName;
	}

	public void setDepartmentName(String departmentName) {
		this.departmentName = departmentName;
	}

	@Override
	public String toString() {
		return "Department [id=" + id + ", departmentName=" + departmentName
				+ "]";
	}
	
}

　　dao层：除了entity层，我们还需要有dao层，用于对于entity的增删改查的操作，这里对应的有EmployeeDao和DepartmentDao

　　EmployeeDao.java

package com.jackie.springmvc.crud.dao;

import java.util.Collection;
import java.util.HashMap;
import java.util.Map;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Repository;

import com.jackie.springmvc.crud.entities.Department;
import com.jackie.springmvc.crud.entities.Employee;

@Repository
public class EmployeeDao {

	private static Map<Integer, Employee> employees = null;
	
	@Autowired
	private DepartmentDao departmentDao;
	
	static{
		employees = new HashMap<Integer, Employee>();

		employees.put(1001, new Employee(1001, "E-AA", "aa@163.com", 1, new Department(101, "D-AA")));
		employees.put(1002, new Employee(1002, "E-BB", "bb@163.com", 1, new Department(102, "D-BB")));
		employees.put(1003, new Employee(1003, "E-CC", "cc@163.com", 0, new Department(103, "D-CC")));
		employees.put(1004, new Employee(1004, "E-DD", "dd@163.com", 0, new Department(104, "D-DD")));
		employees.put(1005, new Employee(1005, "E-EE", "ee@163.com", 1, new Department(105, "D-EE")));
	}
	
	private static Integer initId = 1006;
	
	public void save(Employee employee){
		if(employee.getId() == null){
			employee.setId(initId++);
		}
		
		employee.setDepartment(departmentDao.getDepartment(employee.getDepartment().getId()));
		employees.put(employee.getId(), employee);
	}
	
	public Collection<Employee> getAll(){
		return employees.values();
	}
	
	public Employee get(Integer id){
		return employees.get(id);
	}
	
	public void delete(Integer id){
		employees.remove(id);
	}
}

该dao提供了：1. 添加保存一个employee——save方法

　　　　　　　2. 获取所有员工信息——getAll方法

　　　　　　　3. 根据指定员工id查找员工——get方法

　　　　　　　4. 根据指定员工id删除员工——delete方法

　　DepartmentDao.java

package com.jackie.springmvc.crud.dao;

import java.util.Collection;
import java.util.HashMap;
import java.util.Map;

import org.springframework.stereotype.Repository;

import com.jackie.springmvc.crud.entities.Department;

@Repository
public class DepartmentDao {

	private static Map<Integer, Department> departments = null;
	
	static{
		departments = new HashMap<Integer, Department>();
		
		departments.put(101, new Department(101, "D-AA"));
		departments.put(102, new Department(102, "D-BB"));
		departments.put(103, new Department(103, "D-CC"));
		departments.put(104, new Department(104, "D-DD"));
		departments.put(105, new Department(105, "D-EE"));
	}
	
	public Collection<Department> getDepartments(){
		return departments.values();
	}
	
	public Department getDepartment(Integer id){
		return departments.get(id);
	}
	
}

　　该dao提供了：1. 查找所有部门信息——getDepartments

　　　　　　　2. 根据指定id查找相应的部门信息——getDepartment

　　另外这里需要用到的所有jar包都在这里

　　http://pan.baidu.com/s/1qXT180c　　提取码：z7q2

　　用料齐活了，就开始做菜了，要做的分别是REST清蒸C（添加记录）、REST油炸R（查询记录）、REST红烧U（更新记录）和REST水煮D（删除记录）。

1. 查询记录

　　这个很简单，跟前几篇介绍的套路差不多，新建一个index.jsp，放入一个用于查询的超链接

<a href="emps">list all employees</a><br/>

相应的在Handler中需要添加映射支持，这里新建一个EmployeeHandler类

package com.jackie.springmvc.crud.handlers;

import java.util.Map;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import com.jackie.springmvc.crud.dao.EmployeeDao;

@Controller
public class EmployeeHandler {
	
	@Autowired
	private EmployeeDao employeeDao;
	
	@RequestMapping("/emps")
	public String list(Map<String, Object> map){
		map.put("employees", employeeDao.getAll());
		return "list";
	}

}

注意：

　　这里RequestMapping中没有指明RequestMethod的请求类型，默认是GET方式。

　　最终我们需要将查询的数据解析出来放到页面上，这个页面就是list.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
	<c:if test="${empty requestScope.employees}">
		没有员工信息
	</c:if>
	<c:if test="${!empty requestScope.employees }">
		<table border="1" cellpadding="10" cellspacing="0">
			<tr>
				<th>ID</th>
				<th>LastName</th>
				<th>Email</th>
				<th>Gender</th>
				<th>Department</th>
				<th>Edit</th>
				<th>Delete</th>
			</tr>
			
			<c:forEach items="${requestScope.employees }" var="emp">
				<tr>
					<td>${emp.id }</td>
					<td>${emp.lastName }</td>
					<td>${emp.email }</td>
					<td>${emp.gender==0?‘Female‘:‘Male‘ }</td>
					<td>${emp.department.departmentName }</td>
					<td><a href="emp/${emp.id}">Edit</a></td>
					<td><a class="delete" href="emp/${emp.id}">Delete</a></td>
				</tr>
			</c:forEach>
		</table>
	</c:if>
	<br><br>
</body>
</html>

　　这里通过表格的方式显示，表格的每一行显示一个员工记录。

　　如果Handler层没有传入employee，则显示“没有员工信息”。

　　如果从Handler层传入查询到的employee的信息，则通过遍历的方式查询每条记录并显示在对应的表格中。

　　结果如下：

技术分享

　　这里查询了所有的员工信息，为简便起见，这里的员工信息并不是从数据库中读取的，而是在EmployeeDao中通过静态模块声明构造的，将每个员工信息放入一个map集合中。

2. 添加记录

　　添加记录即在原有的数据集合基础上，再新建一个员工信息，我们需要为员工的每个属性填充值，所以我们需要一个页面来为这些字段赋值，这个页面就叫input.jsp。

　　添加员工信息的入口链接就放在list.jsp中

<a href = "emp">add new employee</a><br/>

　　同时在EmployeeHandler中添加映射

@RequestMapping(value="/emp", method=RequestMethod.GET)
public String input(Map<String, Object> map){
	map.put("departments", departmentDao.getDepartments());
	map.put("employee", new Employee());
	return "input";
}

　　input.jsp

<%@page import="java.util.HashMap"%>
<%@page import="java.util.Map"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ taglib prefix="form" uri="http://www.springframework.org/tags/form" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
 <form:form action="emp" method="POST" modelAttribute="employee">
 	<!-- path 属性对应html表单标签的name属性 -->
 	LastName: <form:input path="lastName"></form:input><br>
 	Email:<form:input path="email"></form:input><br>
 	<%
 		Map<String, String> genders = new HashMap<String, String>();
 		genders.put("1", "male");
 		genders.put("0", "female");
 		request.setAttribute("genders", genders);
 	%>
 	Gender:<form:radiobuttons path="gender" items="${genders }"/><br>
 	Department:<form:select path="department.id" items="${departments }" itemLabel="departmentName" itemValue="id"></form:select><br>
 	<input type="submit" value="Submit"/>
 </form:form>

</body>
</html>

　　先不看代码，至此你就能看到这样的效果：

技术分享

　　到这里还没完，我们还需要写一个保存的handler接口，在EmployeeHandler.java中

@RequestMapping(value="/emp", method=RequestMethod.POST)
public String save(Employee employee){
	employeeDao.save(employee);
	return "redirect:/emps";
}

主要实现将新建的员工记录保存到employee集合中。

这样我们就能够成功的添加一条记录了

技术分享

注意：

　　这里有几个问题需要声明

　　(1). 为什么使用form标签:可以更快速开发表单页面，而且可以方便的进行表单值的回显

　　(2) 为什么要在EmployeeHandler类中添加map.put("employee", employee),并且在input.jsp页面的form:form标签中添加modelAttribute="employee"

　　如果没有这样的声明代码，在运行中会出现报错信息如下：

HTTP Status 500 - An exception occurred processing JSP page /WEB-INF/views/input.jsp at line 23
type Exception report
message An exception occurred processing JSP page /WEB-INF/views/input.jsp at line 23
description The server encountered an internal error that prevented it from fulfilling this request.
exception
org.apache.jasper.JasperException: An exception occurred processing JSP page /WEB-INF/views/input.jsp at line 23

20:  -->
21:  <form:form action="emp" method="POST">
22:  	<!-- path 灞炴?у搴攈tml琛ㄥ崟鏍囩鐨刵ame灞炴?? -->
23:  	LastName: <form:input path="lastName"></form:input><br>
24:  	Email:<form:input path="email"></form:input><br>
25:  	<%
26:  		Map<String, String> genders = new HashMap<String, String>();


Stacktrace:
	org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:574)
	org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:471)
	org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:396)
	org.apache.jasper.servlet.JspServlet.service(JspServlet.java:340)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
	org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:209)
	org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:267)
	org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1221)
	org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1005)
	org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:952)
	org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:870)
	org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
	org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:852)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
	org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
	org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:77)
	org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
root cause
java.lang.IllegalStateException: Neither BindingResult nor plain target object for bean name ‘command‘ available as request attribute
	org.springframework.web.servlet.support.BindStatus.<init>(BindStatus.java:144)
	org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.getBindStatus(AbstractDataBoundFormElementTag.java:168)
	org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.getPropertyPath(AbstractDataBoundFormElementTag.java:188)
	org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.getName(AbstractDataBoundFormElementTag.java:154)
	org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.autogenerateId(AbstractDataBoundFormElementTag.java:141)
	org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.resolveId(AbstractDataBoundFormElementTag.java:132)
	org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.writeDefaultAttributes(AbstractDataBoundFormElementTag.java:116)
	org.springframework.web.servlet.tags.form.AbstractHtmlElementTag.writeDefaultAttributes(AbstractHtmlElementTag.java:422)
	org.springframework.web.servlet.tags.form.InputTag.writeTagContent(InputTag.java:142)
	org.springframework.web.servlet.tags.form.AbstractFormTag.doStartTagInternal(AbstractFormTag.java:84)
	org.springframework.web.servlet.tags.RequestContextAwareTag.doStartTag(RequestContextAwareTag.java:80)
	org.apache.jsp.WEB_002dINF.views.input_jsp._jspx_meth_form_005finput_005f0(input_jsp.java:244)
	org.apache.jsp.WEB_002dINF.views.input_jsp._jspService(input_jsp.java:168)
	org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
	org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:438)
	org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:396)
	org.apache.jasper.servlet.JspServlet.service(JspServlet.java:340)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
	org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:209)
	org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:267)
	org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1221)
	org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1005)
	org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:952)
	org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:870)
	org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
	org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:852)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
	org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
	org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:77)
	org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
note The full stack trace of the root cause is available in the Apache Tomcat/8.0.36 logs.

　　于是在handler中将employee放入map集合中，此时运行，仍然报错

HTTP Status 500 - java.lang.IllegalStateException: Neither BindingResult nor plain target object for bean name ‘command‘ available as request attribute
type Exception report
message java.lang.IllegalStateException: Neither BindingResult nor plain target object for bean name ‘command‘ available as request attribute
description The server encountered an internal error that prevented it from fulfilling this request.
exception
org.apache.jasper.JasperException: java.lang.IllegalStateException: Neither BindingResult nor plain target object for bean name ‘command‘ available as request attribute
	org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:555)
	org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:471)
	org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:396)
	org.apache.jasper.servlet.JspServlet.service(JspServlet.java:340)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
	org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:209)
	org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:267)
	org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1221)
	org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1005)
	org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:952)
	org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:870)
	org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
	org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:852)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
	org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
	org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:77)
	org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
root cause
java.lang.IllegalStateException: Neither BindingResult nor plain target object for bean name ‘command‘ available as request attribute
	org.springframework.web.servlet.support.BindStatus.<init>(BindStatus.java:144)
	org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.getBindStatus(AbstractDataBoundFormElementTag.java:168)
	org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.getPropertyPath(AbstractDataBoundFormElementTag.java:188)
	org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.getName(AbstractDataBoundFormElementTag.java:154)
	org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.autogenerateId(AbstractDataBoundFormElementTag.java:141)
	org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.resolveId(AbstractDataBoundFormElementTag.java:132)
	org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.writeDefaultAttributes(AbstractDataBoundFormElementTag.java:116)
	org.springframework.web.servlet.tags.form.AbstractHtmlElementTag.writeDefaultAttributes(AbstractHtmlElementTag.java:422)
	org.springframework.web.servlet.tags.form.InputTag.writeTagContent(InputTag.java:142)
	org.springframework.web.servlet.tags.form.AbstractFormTag.doStartTagInternal(AbstractFormTag.java:84)
	org.springframework.web.servlet.tags.RequestContextAwareTag.doStartTag(RequestContextAwareTag.java:80)
	org.apache.jsp.WEB_002dINF.views.input_jsp._jspx_meth_form_005finput_005f0(input_jsp.java:244)
	org.apache.jsp.WEB_002dINF.views.input_jsp._jspService(input_jsp.java:168)
	org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
	org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:438)
	org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:396)
	org.apache.jasper.servlet.JspServlet.service(JspServlet.java:340)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
	org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:209)
	org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:267)
	org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1221)
	org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1005)
	org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:952)
	org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:870)
	org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
	org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:852)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
	org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
	org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:77)
	org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
note The full stack trace of the root cause is available in the Apache Tomcat/8.0.36 logs.

　　这时候在form:form中加入modelAttribute="employee"，再次运行，就能够成功添加记录了。

　　这是为什么呢，因为表单在显示的时候会做一个检查，如果表单的字段在request的bean中不能一一对应，就会无法显示并报错，说白了就是这里加上了employee这个bean后，这个对象中的各个属性如email、gender和表单上的字段都能够对应起来了，校验通过，就能正常添加保存了。

　　注意input.jsp中modelAttribute的值要和handler中放进map集合的key值一致，默认在页面上这个modelAttribute的值为command,所以你会看到报错信息中频繁的出现command。

　　(3). <form:radiobuttons>这个标签中有一下属性：

　　　　items：存放具体的数据集合，可以是String、Map或List类型

　　　　itemValue：指定radio的value值，可以使集合中bean的一个属性值

　　　　itemLabel：radio的label值

3. 删除记录

　　其实从前面的list.jsp的表格中已经看出来了，在每条记录后面都有一个DELETE选项，用于删除该项记录，那么具体怎么实现

　　这里首先要该Delete项对应的href，在list.jsp中

<td><a href="emp/${emp.id}">Delete</a></td>

　　我们将href的值赋值为一个请求路径，显然我们需要在handler中添加映射处理：

@RequestMapping(value="/emp/{id}", method=RequestMethod.DELETE)
public String delete(@PathVariable("id") Integer id){
	employeeDao.delete(id);
	return "redirect:/emps";
}

　　删除完记录后重定向到emps即list.jsp页面。

　　效果如下

技术分享

注意：

　　(1). 这里要明白，实际上我们在页面上发送的是一个rest的delete请求，但是通过<a href>的超链接方式我们只能发送get请求，而且前面我们说过，对于form来说只能发get和post请求，如果要发delete和put，则需要伪装成post请求，再在handler处理类中进行解析处理。

　　对于这个问题，我们想到了jquery，于是引入jquery库到WebContent/scripts目录下，版本是1.9.1

　　首先需要一个form表单，因为无可厚非，只有表单才能提交post请求

<form action="" method="POST">
	<input type="hidden" name="_method" value="DELETE"/>
</form>

　　在list.jsp中引入jquery库

<script type="text/javascript" src="scripts/jquery-1.9.1.min.js"></script>

　　在delete对应的<a>中加入class=“delete”，方便后面使用jquery进行元素定位

　　写入功能实现代码：

<script type="text/javascript">
	$(function(){
		$(".delete").click(function(){
			var href = $(this).attr("href");
			$("form").attr("action", href).submit();
			return false;
		});
	})
</script>

　这段代码的意思无非就是：找到delete删除元素，提取器href属性值，并将其赋给新添加的form表单中，当点击超链接后相当于提交form，并移交给定义好的hanlder接口。

　　(2). 又要啰嗦下，对于静态资源来说，因为我们在web.xml中声明spring是拦截了所有请求，所以对于静态资源我们也统统招收，拦截不误，但是显然我们没有与这个静态资源对应的映射，也就是说spring拦截下来了，却没有能力处理，这里介绍在springmvc.xml中添加两个标签就能解决问题

<mvc:default-servlet-handler/> 
<mvc:annotation-driven></mvc:annotation-driven>

　　在前面的章节中有介绍过其他的方法，就是在web.xml中声明各种静态资源的支持，比较繁琐傻瓜点^^

　　(3). 为什么添加了这个<mvc:default-servlet-handler/>就能解决问题：

　　Default-servlet-handler将在SpringMVC上下文中定义一个DefaultServletHttpRequestHandler，它会对进入DispatcherServlet的请求进行筛查，如果发现是没有经过映射的请求，就将该请求交由WEB应用服务器默认的Servlet处理。如果不是静态资源的请求，才由DispatcherServlet继续处理。

　　一般WEB应用服务器默认的Servlet的名称都是default，若所使用的WEB服务器的默认Serlvet名称不是default，则需要通过default-servlet-name属性显示指定。

　　这里的小问题比较多，不知道你晕了没，但是到目前为止，好像一个简易的框架就有了，有了后台的java，还有模板jsp技术，以及对于dom操作的Jquery，当然我们还少了一个真正的数据库。

4. 更新记录

　　更新操作实际上是分为两步：查找要修改的记录 + 修改记录并保存

　　(1). 查找记录

　　通过get方式映射到emp/${id}

　　与delete选项类似，在list.jsp改为

<td><a href="emp/${emp.id}">Edit</a></td>

　　同时在Handler添加相应映射

@RequestMapping(value="/emp/{id}", method=RequestMethod.GET)
public String input(@PathVariable("id") Integer id, Map<String, Object> map){
	map.put("employee", employeeDao.get(id));
	map.put("departments", departmentDao.getDepartments());
	return "input";
}

　　这样就可以定位到选中的employee对象上，并跳转到input.jsp界面上。

　　(2). 修改并保存

　　这里要说清楚，进入input.jsp页面会有两种情况，一种是添加一条Employee记录，二是修改一条Employee记录，而且我们从前面的界面可以看出我们并不修改LastName这个字段，那我们如果让input.jsp具有辨识是从添加记录那还是修改记录那跳转过来的呢，于是我们需要在input.jsp中加入判断

 <c:if test="${employee.id == null }">
		<!-- path 属性对应 html 表单标签的 name 属性值 -->
			LastName: <form:input path="lastName" />
			<form:errors path="lastName"></form:errors>
		</c:if>
		<c:if test="${employee.id != null }">
			<form:hidden path="id" />
			<input type="hidden" name="_method" value="PUT" />
</c:if>

　　如果传过来的employee中id存在，那说明是修改更新，如果为空，说明是新建一条记录。

　　同时，老套路，这里还是利用隐藏域hidden来发送一个put请求到handler

　　在EmployeeHandler中

@ModelAttribute
public void getEmployee(@RequestParam(value="id",required=false) Integer id,
		Map<String, Object> map){
		if(id != null){
			map.put("employee", employeeDao.get(id));
		}
}
	
@RequestMapping(value="/emp", method=RequestMethod.PUT)
public String update(Employee employee){
	employeeDao.save(employee);
	return "redirect:/emps";
}

　　之所以这里有ModelAttribute前篇已经说过，如果没有话，更新完后这个LastName字段就会为空。

　　最终效果如下：

技术分享