2.0springmvc uses restful

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RESTful

1、RESTful brief introduction

REST：Representational State Transfer, Presentation layer resource state transition .

a> resources

     resources It is a kind of look Wait for the server The way , namely , Think of the server as composed of many discrete resources . Each resource is a nameable abstraction on the server . Because resource is an abstract concept , So it can not only represent a file in the server file system 、 A table in the database and so on , We can design resources as abstract as possible , As long as imagination allows and client application developers can understand . Similar to object-oriented design , Resources are organized around terms , The first concern is the noun . A resource can be made up of one or more URI To mark .URI Is the name of the resource , It's also resources Web Address on . Client applications interested in a resource , The URI Interact with it .

b> Expression of resources

     The expression of resources is a paragraph about resources In a certain Specific moment Of state Of describe . Can be on the client side - Transfer between servers （ In exchange for ）. Resources can be expressed in a variety of formats , for example HTML/XML/JSON/ Pure text / picture / video / Audio and so on. . The presentation format of resources can be determined by negotiation mechanism . request - The response direction is usually expressed in different formats .

c> State shift

     State transition is about ： stay client and Server side Between Transfer （transfer） Representation of resource status . By transferring and manipulating the expression of resources , To achieve the purpose of operating resources indirectly .

2、RESTful The implementation of the

     specifically , Namely HTTP In the agreement , Four represent the operation mode It's a simple verb ：GET、POST、PUT、DELETE.

     They correspond to four basic operations ：GET Used to obtain resources ,POST Used to create a new resource ,PUT Used to update resources ,DELETE Used to delete resources .

    REST Style advocates URL Address using Unified style design , Use the words from front to back Slashes separate , Do not use question mark key values Carry on the way Request parameters , Instead, the data to be sent to the server is used as URL Part of the address , To ensure the consistency of the overall style .

operation	The traditional way	REST style
Query operation	getUserById?id=1	user/1–>get Request mode
Save operation	saveUser	user–>post Request mode
Delete operation	deleteUser?id=1	user/1–>delete Request mode
update operation	updateUser	user–>put Request mode

3、HiddenHttpMethodFilter filter

     Because the browser only supports sending get and post Method request , So how to send put and delete What about the request ？

    SpringMVC Provides HiddenHttpMethodFilter Help us take POST Request conversion to DELETE or PUT request

HiddenHttpMethodFilter Handle put and delete The condition of the request ：

• Request mode of current request It has to be for post

• The current request must be transmitted Request parameters _method

     Meet the above conditions ,HiddenHttpMethodFilter The filter will convert the request mode of the current request into request parameters _method Value , So request parameters ==_method== The value of is the final request method

stay web.xml Register in HiddenHttpMethodFilter

<!-- Configure how requests are processed put and delete Of HiddenHttpMethodFilter-->
<filter>
    <filter-name>HiddenHttpMethodFilter</filter-name>
    <filter-class>org.springframework.web.filter.HiddenHttpMethodFilter</filter-class>
</filter>
<filter-mapping>
    <filter-name>HiddenHttpMethodFilter</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

Source code

/*  filter   There must be three ways  ① initialization （ important ） ② filtering  ③ Three methods of destruction   Mode one :  How to perform filtering doFilter Who has executed it   The subclass is not looking for the parent class   Mode two :  The search parameter is  filterChain  It must be the method of performing filtering  filterChain  For release  */ 
public class HiddenHttpMethodFilter extends OncePerRequestFilter {
    
    private static final List<String> ALLOWED_METHODS;
    public static final String DEFAULT_METHOD_PARAM = "_method";
    private String methodParam = "_method";

    public HiddenHttpMethodFilter() {
    
    }

    public void setMethodParam(String methodParam) {
    
        Assert.hasText(methodParam, "'methodParam' must not be empty");
        this.methodParam = methodParam;
    }

    // The search parameter is  filterChain  It must be the method of performing filtering  filterChain  For release  ( How to perform filtering )
    //HttpServletRequest request, HttpServletResponse response  Filtering is the interception of requests   and   Respond to 
    protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain) throws ServletException, IOException {
    

        HttpServletRequest requestToUse = request; //  The assignment is  HttpServletRequest  object 

        //  Get request parameters   Is it equal to  POST  Constant for the  true
        if ("POST".equals(request.getMethod()) && request.getAttribute("javax.servlet.error.exception") == null) {
    
            //  Get request parameters  this.methodParam private String methodParam = "_method"; ( The value of a constant )
            String paramValue = request.getParameter(this.methodParam);
            if (StringUtils.hasLength(paramValue)) {
     //  Is there a length   Is it empty 
                String method = paramValue.toUpperCase(Locale.ENGLISH); //  take _method  Converts the value of to uppercase 
                if (ALLOWED_METHODS.contains(method)) {
     // Can only write  PUT DELETE PATCH  Here's the explanation 
                    // requestToUse  Assign him a value   Turned into  PUT DELETE PATCH
                    requestToUse = new HiddenHttpMethodFilter.HttpMethodRequestWrapper(request, method);
                }
            }
        }
        //  At the time of release   The newly created request object   As a   Filter intercepted objects   Released 
        filterChain.doFilter((ServletRequest)requestToUse, response);//  The results obtained in the future are  PUT DELETE PATCH
    }

    static {
    
        //List  combination  //  Put the last three values in list In combination  HttpMethod enumeration 
        ALLOWED_METHODS = Collections.unmodifiableList(Arrays.asList(HttpMethod.PUT.name(), HttpMethod.DELETE.name(), HttpMethod.PATCH.name()));
    }

    private static class HttpMethodRequestWrapper extends HttpServletRequestWrapper {
    
        private final String method;  // ② PUT DELETE PATCH

        public HttpMethodRequestWrapper(HttpServletRequest request, String method) {
    
            super(request);
            this.method = method; // ① PUT DELETE PATCH
        }

        public String getMethod() {
    
            return this.method; // ③ PUT DELETE PATCH
        }
    }
}

notes ：

     When there are multiple filters , The order of filter execution is determined , The more advanced the configuration , Just execute
    
     So far, ,SpringMVC Two filters are provided in ：CharacterEncodingFilter and HiddenHttpMethodFilter

stay web.xml Registration in China , Must first register CharacterEncodingFilter, To register again HiddenHttpMethodFilter

reason ：

• stay CharacterEncodingFilter Pass through request.setCharacterEncoding(encoding) Method to set the value of the character set

• request.setCharacterEncoding(encoding) Method requires that there must be no previous operation to get the request parameters

• and HiddenHttpMethodFilter There is just one operation to get the request mode ：

• String paramValue = request.getParameter(this.methodParam);
  

RESTful Case study

1、 preparation

And traditional CRUD equally , Realize the addition, deletion, modification and query of employee information .

• Set up the environment

• Prepare entity classes

  public class Employee {
        
  
     private Integer id;
     private String lastName;
  
     private String email;
     //1 male, 0 female
     private Integer gender;
     
     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 Employee(Integer id, String lastName, String email, Integer gender) {
        
        super();
        this.id = id;
        this.lastName = lastName;
        this.email = email;
        this.gender = gender;
     }
  
     public Employee() {
        
     }
  }
  

• Get ready dao Analog data

  import java.util.Collection;
  import java.util.HashMap;
  import java.util.Map;
  
  import com.atguigu.mvc.bean.Employee;
  import org.springframework.stereotype.Repository;
  
  
  @Repository // Persistent layer by layer component database 
  public class EmployeeDao {
        
  
      private static Map<Integer, Employee> employees = null;
  
      static{
        
          employees = new HashMap<Integer, Employee>();
  
          employees.put(1001, new Employee(1001, "E-AA", "[email protected]", 1));
          employees.put(1002, new Employee(1002, "E-BB", "[email protected]", 1));
          employees.put(1003, new Employee(1003, "E-CC", "[email protected]", 0));
          employees.put(1004, new Employee(1004, "E-DD", "[email protected]", 0));
          employees.put(1005, new Employee(1005, "E-EE", "[email protected]", 1));
      }
  
      private static Integer initId = 1006;
  
      //  add to   and   modify   function 
      public void save(Employee employee){
        
          if(employee.getId() == null){
        
              employee.setId(initId++); //  Assign first   Increasing 
          }
          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);
      }
  }
  

2、 Feature list

function	URL Address	Request mode
Visit the home page √	/	GET
Query all data √	/employee	GET
Delete √	/employee/2	DELETE
Jump to the add data page √	/toAdd	GET
Perform save √	/employee	POST
Jump to the update data page √	/employee/2	GET
Perform the update √	/employee	PUT

3、 Specific function ： Visit the home page

a> To configure view-controller

<mvc:view-controller path="/" view-name="index"/>

b> Create a page

<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8" >
    <title>Title</title>
</head>
<body>
<h1> home page </h1>
<a th:href="@{/employee}"> Access employee information </a>
</body>
</html>

4、 Specific function ： Query all employee data

a> Controller method

@RequestMapping(value = "/employee", method = RequestMethod.GET)
public String getEmployeeList(Model model){
    
    Collection<Employee> employeeList = employeeDao.getAll();
    model.addAttribute("employeeList", employeeList);
    return "employee_list";
}

b> establish employee_list.html

<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8">
    <title>Employee Info</title>
    <script type="text/javascript" th:src="@{/static/js/vue.js}"></script>
</head>
<body>
	<!-- Margin  = 1 ,  Cancel margins ,  Cancel spacing   In the middle -->
    <table border="1" cellpadding="0" cellspacing="0" style="text-align: center;" id="dataTable">
        <tr>
            <th colspan="5">Employee Info</th>
        </tr>
        <tr>
            <th>id</th>
            <th>lastName</th>
            <th>email</th>
            <th>gender</th>
            <th>options(<a th:href="@{/toAdd}">add</a>)</th>
        </tr>
        <tr th:each="employee : ${employeeList}">
            <td th:text="${employee.id}"></td>
            <td th:text="${employee.lastName}"></td>
            <td th:text="${employee.email}"></td>
            <td th:text="${employee.gender}"></td>
            <td>
                <!-- Wrong way of writing : {  It will be resolved to  %7B }  It will be resolved to  %7D-->
                <!--<a th:href="@{/employee/${employee.id}}">delete</a>-->
                <!-- Mode one :-->
                    <a @click="deleteEmployee" th:href="@{
     '/employee/'+${employee.id}}">delete</a>
                <!-- Mode two :-->
                    <a th:href="@{
     '/employee/'+${employee.id}}">update</a>
            </td>
        </tr>
    </table>
</body>
</html>

5、 Specific function ： Delete a key

a> Create processing delete Request Form

<!--  effect ： Control the submission of forms through hyperlinks , take post Request conversion to delete request  -->
<form id="delete_form" method="post">
    <!-- HiddenHttpMethodFilter requirement ： Must transmit _method Request parameters , And the value is the final request method  -->
    <input type="hidden" name="_method" value="delete"/>
</form>

b> Delete hyperlink binding click event

• introduce vue.js

<script type="text/javascript" th:src="@{/static/js/vue.js}"></script>

• Create hyperlinks

                <!-- Wrong way of writing : {  It will be resolved to  %7B }  It will be resolved to  %7D-->
                <!--<a th:href="@{/employee/${employee.id}}">delete</a>-->
                <!-- Mode one :-->
                    <a @click="deleteEmployee" th:href="@{
     '/employee/'+${employee.id}}">delete</a>
                <!-- Mode two :-->
                    <a th:href="@{
     '/employee/'+${employee.id}}">update</a>

• adopt vue Handle click events

    <script type="text/javascript"> var vue = new Vue({
       el:"#dataTable", methods:{
       deleteEmployee:function (event) {
       // according to id Get form elements  var deleteForm = document.getElementById("deleteForm"); // The of the hyperlink that will trigger the click event href Property is assigned to the of the form action deleteForm.action = event.target.href; // Submit Form  deleteForm.submit(); // Cancel the default behavior of hyperlinks  event.preventDefault(); } } }); </script>

c> Controller method

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

6、 Specific function ： Jump to the add data page

a> To configure view-controller

<mvc:view-controller path="/toAdd" view-name="employee_add"></mvc:view-controller>

b> establish employee_add.html

<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8">
    <title>Add Employee</title>
</head>
<body>

<form th:action="@{/employee}" method="post">
    lastName:<input type="text" name="lastName"><br>
    email:<input type="text" name="email"><br>
    gender:<input type="radio" name="gender" value="1">male
    <input type="radio" name="gender" value="0">female<br>
    <input type="submit" value="add"><br>
</form>

</body>
</html>

* 7、 Specific function ： Perform save

a> Controller method

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

8、 Specific function ： Jump to the update data page

a> Modify hyperlinks

<a th:href="@{
     '/employee/'+${employee.id}}">update</a>

b> Controller method

@RequestMapping(value = "/employee/{id}", method = RequestMethod.GET)
public String getEmployeeById(@PathVariable("id") Integer id, Model model){
    
    Employee employee = employeeDao.get(id);
    model.addAttribute("employee", employee);
    return "employee_update";
}

c> establish employee_update.html

<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8">
    <title>Update Employee</title>
</head>
<body>

<form th:action="@{/employee}" method="post">
    <input type="hidden" name="_method" value="put">
    <input type="hidden" name="id" th:value="${employee.id}"> <!-- The echo data ${}-->
    lastName:<input type="text" name="lastName" th:value="${employee.lastName}"><br>
    email:<input type="text" name="email" th:value="${employee.email}"><br>
    <!-- th:field="${employee.gender}" Can be used to echo radio boxes or check boxes   If the radio box value and employee.gender The value is consistent. , Then add checked="checked" attribute  -->
    gender:<input type="radio" name="gender" value="1" th:field="${employee.gender}">male
    <input type="radio" name="gender" value="0" th:field="${employee.gender}">female<br>
    <input type="submit" value="update"><br>
</form>

</body>
</html>

9、 Specific function ： Perform the update

a> Controller method

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