Table of contents
3.1 Collection of simple data types
3.2 Collection of object data types
Related readings of previous columns & articles
4. Spring MVC series of columns
1. Simple data types
In Servlet, we get request parameters through request.getParameter(name). There are two problems with this method:
- Code redundancy occurs when there are many request parameters.
- tightly coupled with the container
SpringMVC supports parameter injection to obtain request data, that is, request parameters are directly encapsulated into method parameters. The usage is as follows:
1.1 Controller method
// 获取简单类型参数
@RequestMapping("/c1/param1")
public void simpleParam(String username,int age){
System.out.println(username+" "+age);
}
Since we have not configured the corresponding param1 page, this is to directly print out the accessed parameters on the console. When accessing this method, the request parameter name is the same as the method parameter name to complete automatic encapsulation. and print it out on the console. The execution path is: http://localhost:8080/c1/param1?username=LYL&age=19
1.2 Test results
OK, it is indeed successfully output on the console, indicating that the encapsulation is successful. Next, let's talk about the object type.
2. Object type
SpringMVC supports directly encapsulating parameters as objects. First, we create a new student class. as follows:
Student
package com.example.domain;
public class Student {
private int id;
private String name;
private String sex;
public Student() {
}
public Student(int id, String name, String sex) {
this.id = id;
this.name = name;
this.sex = sex;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
@Override
public String toString() {
return "Student[ " +
"id=" + id +
", name='" + name + '\'' +
", sex='" + sex + '\'' +
" ]";
}
}
2.1 Single object
2.1.1 Controller methods
// 获取对象类型参数
@RequestMapping("/c1/param2")
public void objParam(Student student){
System.out.println(student);
}
You can know that we will print out the specific information of the students on the console,
Access path: http://localhost:8080/c1/param2?id=1&name=LYL&sex=man
2.1.2 Test results
OK, it is indeed printed on the console, indicating that when we encapsulate the object type, we only need to put their attributes in the parameters of the access path
2.2 Associated objects
To realize the encapsulation of associated objects, first we have to create an Address address class, and then add an Address type attribute in the Student class. as follows:
Address：
package com.example.domain;
public class Address {
// 地址信息
private String info;
// 邮编
private String postcode;
public String getInfo() {
return info;
}
public void setInfo(String info) {
this.info = info;
}
public String getPostcode() {
return postcode;
}
public void setPostcode(String postcode) {
this.postcode = postcode;
}
@Override
public String toString() {
return "Address[ " +
"info='" + info + '\'' +
", postcode='" + postcode + '\'' +
" ]";
}
}
Remember to modify the Student class as follows:
package com.example.domain;
import java.util.List;
import java.util.Map;
public class Student {
private int id;
private String name;
private String sex;
// 地址对象
//private Address address;
public Student() {
}
public Student(int id, String name, String sex) {
this.id = id;
this.name = name;
this.sex = sex;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
public Address getAddress() {
return address;
}
public void setAddress(Address address) {
this.address = address;
}
@Override
public String toString() {
return "Student[ " +
"id=" + id +
", name='" + name + '\'' +
", sex='" + sex + '\'' +
", address='" + address + '\'' +
" ]";
}
}
2.2.1 Controller methods
// 获取关联对象类型参数
@RequestMapping("c1/param3")
public void objParam2(Student student){
System.out.println(student);
}
When accessing this method, the request parameter name is the same as the attribute name of the method parameter, and then automatic encapsulation can be completed. , so we can write the request path as: http://localhost:8080/c1/param3?id=1&name=HQX&sex=woman&address.info=guangzhou&address.postcode=5201314
2.2.2 Test results
OK, it can be clearly seen that it can be successfully queried.
3. Collection type
SpringMVC supports the encapsulation of parameters as a List or Map collection. The following demonstrates how to encapsulate a collection of simple data types. as follows:
3.1 Collection of simple data types
3.1.1 Control method
// 绑定简单数据类型List参数，参数前必须添加@RequestParam注解
@RequestMapping("/c/param4")
public void listParam(@RequestParam List<String> users){
users.forEach(System.out::println);
}
It can be seen from the code that this collection will be traversed in the console after access.
The access path is as follows: http://localhost:8080/c/param4?users=LYL&users=HQX
3.1.2 Test results
OK, indeed successfully printed out on the console.
3.2 Collection of object data types
SpringMVC does not support encapsulating parameters into a List collection of object type, but it can be encapsulated into an object with a List property. Here we have to add a collection object to the Student class first. It is written as follows:
Student
package com.example.domain;
import java.util.List;
import java.util.Map;
public class Student {
private int id;
private String name;
private String sex;
// 地址集合List
private List<Address> address;
public Student() {
}
public Student(int id, String name, String sex) {
this.id = id;
this.name = name;
this.sex = sex;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
public List<Address> getAddress() {
return address;
}
public void setAddress(List<Address> address) {
this.address = address;
}
@Override
public String toString() {
return "Student[ " +
"id=" + id +
", name='" + name + '\'' +
", sex='" + sex + '\'' +
", address='" + address + '\'' +
" ]";
}
}
3.2.1 Controller methods
// 对象中包含集合属性
@RequestMapping("c1/param6")
public void listParam6(Student student){
System.out.println(student);
}In fact, it is no different from the above object types, mainly because the attributes of the parameter types are different, and the access paths are different.
3.2.2 Test results
OK, it can also be successfully queried
3.3 Map collection
Similarly, if SpringMVC wants to encapsulate the Map collection, it needs to be encapsulated into an object with a Map attribute. Modify the Student entity class as follows:
Student
package com.example.domain;
import java.util.List;
import java.util.Map;
public class Student {
private int id;
private String name;
private String sex;
// 地址集合Map
private Map<String,Address> address;
public Student() {
}
public Student(int id, String name, String sex) {
this.id = id;
this.name = name;
this.sex = sex;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
public Map<String, Address> getAddress() {
return address;
}
public void setAddress(Map<String, Address> address) {
this.address = address;
}
@Override
public String toString() {
return "Student[ " +
"id=" + id +
", name='" + name + '\'' +
", sex='" + sex + '\'' +
", address='" + address + '\'' +
" ]";
}
}
3.3.1 Controller methods
// 对象中包含Map属性
@RequestMapping("c1/param7")
public void mapParam(Student student){
System.out.println(student);
}Access path:
3.3.2 Test results
OK, it was also successfully detected. As for why the info of the first two is empty, it is because I missed a ']', so there was a little episode, but it does not affect our continued output.
Related readings of previous columns & articles
If you don’t know anything about the content of this issue, you can also go to the previous issues. The following is a series of column articles such as Maven and Mybatis carefully crafted by bloggers in the past. Don’t miss it when you pass by! If it is helpful to you, please like it and bookmark it. Among them, some of the Spring columns are being updated, so they cannot be viewed, but they can be viewed after the bloggers have completed all the updates.
1. Maven series of columns
| Maven Series Column | Maven project development |
| Maven aggregation development [example detailed explanation --- 5555 words] |