在程序员的日常工作中,Web开发应该是占比很重的一部分,至少我工作以来,开发的系统基本都是Web端访问的系统,Web开发在这几年也是经历了很快的发展,前端也显得越来越重要,现在很多大一点的公司都实行前后端分离,让后端和前端只专注于自己的事,所谓术业有专攻,我个人也非常建议前后端分离。
既然前后端分离了,那么后端肯定需要提供Web Api接口给到前端,并返回前端需要的数据。
在Spring Boot中,开发Web Api接口主要使用以下几个注解:
- @Controller
- @ResponseBody
- @RestController
- @RequestMapping
- @PathVariable
其实,这些注解在Spring MVC里都有了,所以Spring Boot里的用法也和Spring MVC里基本一样。
在Spring Boot之所以能使用,是因为在spring-boot-starter-web 这个starter pom中,已经引用了spring-web和spring-webmvc。
接下来,我们通过具体例子来讲解下各个注解的使用方法。
1.@Controller
新建控制器HelloController,添加@Controller注解,添加1个方法sayHello,添加@RequestMapping注解,代码如下:
package com.zwwhnly.springbootdemo.controller;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
@Controller
public class HelloController {
@RequestMapping(value = \"/hello\", method = RequestMethod.GET)
public String sayHello() {
return \"hello\";
}
}
运行项目,在浏览器输入http://localhost:8080/hello访问,发现报如下错误:
报错的原因是未找到对应的模板,那么如何解决呢?
我们先讲解下第一种解决方法,添加下thymeleaf模板,首先修改pom文件,添加如下配置:
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-thymeleaf</artifactId>
</dependency>
如果没有设置自动导入maven包的话,IDEA右下角会提示你导入,点击“Import Changes”。
然后在resources/templates目录下,新建hello.html文件(内容先随便写),再次运行项目,访问http://localhost:8080/hello,发现访问正常:
2.@ResponseBody
还有一种更简单的方法是在控制器上添加@ResponseBody注解:
package com.zwwhnly.springbootdemo.controller;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.ResponseBody;
@Controller
@ResponseBody
public class HelloController {
@RequestMapping(value = \"/hello\", method = RequestMethod.GET)
public String sayHello() {
return \"hello\";
}
}
此时的运行结果(直接返回字符串):
hello
3.@RestController
@RestController是Spring4.0推出的组合注解,相当于@Controller+@ResponseBody,我们看下它的源码,也能看出:
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Controller
@ResponseBody
public @interface RestController {
@AliasFor(
annotation = Controller.class
)
String value() default \"\";
}
此时我们就可以将代码简化为:
@RestController
public class HelloController {
@RequestMapping(value = \"/hello\", method = RequestMethod.GET)
public String sayHello() {
return \"hello\";
}
}
4.@RequestMapping
@RequestMapping注解主要用来配置url映射,既可以添加到控制器上,也可以添加到控制器下的方法上,添加到方法上是对添加到控制器上的补充,举例说明:
新建图书类Book:
package com.zwwhnly.springbootdemo.model;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
public class Book {
private Integer bookId;
private String bookName;
private String bookAuthor;
private Date purchaseDate;
public Book(Integer bookId, String bookName, String bookAuthor, String purchaseDate) throws ParseException {
SimpleDateFormat simpleDateFormat = new SimpleDateFormat(\"yyyy-MM-dd\");
this.bookId = bookId;
this.bookName = bookName;
this.bookAuthor = bookAuthor;
this.purchaseDate = simpleDateFormat.parse(purchaseDate);
}
public Integer getBookId() {
return bookId;
}
public void setBookId(Integer bookId) {
this.bookId = bookId;
}
public String getBookName() {
return bookName;
}
public void setBookName(String bookName) {
this.bookName = bookName;
}
public String getBookAuthor() {
return bookAuthor;
}
public void setBookAuthor(String bookAuthor) {
this.bookAuthor = bookAuthor;
}
public Date getPurchaseDate() {
return purchaseDate;
}
public void setPurchaseDate(Date purchaseDate) {
this.purchaseDate = purchaseDate;
}
}
在HelloController中添加方法getBookList:
@RequestMapping(value = \"/getBookList\", method = RequestMethod.GET)
public List<Book> getBookList() {
List<Book> books = new ArrayList<>();
try {
Book book1 = new Book(1, \"平凡的世界\", \"路遥\", \"2010-01-01\");
Book book2 = new Book(2, \"人生\", \"路遥\", \"2011-01-01\");
books.add(book1);
books.add(book2);
} catch (ParseException e) {
e.printStackTrace();
}
return books;
}
运行项目在浏览器输入http://localhost:8080/getBookList,结果为:
// 20190424140621
// http://localhost:8080/getBookList
[
{
\"bookId\": 1,
\"bookName\": \"平凡的世界\",
\"bookAuthor\": \"路遥\",
\"purchaseDate\": \"2009-12-31 16:00:00\"
},
{
\"bookId\": 2,
\"bookName\": \"人生\",
\"bookAuthor\": \"路遥\",
\"purchaseDate\": \"2010-12-31 16:00:00\"
}
]
然后我们在HelloController上也加上@RequestMapping注解:
package com.zwwhnly.springbootdemo.controller;
import com.zwwhnly.springbootdemo.model.Book;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;
import java.text.ParseException;
import java.util.ArrayList;
import java.util.List;
@RestController
@RequestMapping(value = \"hello\")
public class HelloController {
@RequestMapping(value = \"/hello\", method = RequestMethod.GET)
public String sayHello() {
return \"hello\";
}
@RequestMapping(value = \"/getBookList\", method = RequestMethod.GET)
public List<Book> getBookList() {
List<Book> books = new ArrayList<>();
try {
Book book1 = new Book(1, \"平凡的世界\", \"路遥\", \"2010-01-01\");
Book book2 = new Book(2, \"人生\", \"路遥\", \"2011-01-01\");
books.add(book1);
books.add(book2);
} catch (ParseException e) {
e.printStackTrace();
}
return books;
}
}
此时两个方法的访问地址就分别变为了:http://localhost:8080/hello/hello,http://localhost:8080/hello/getBookList。
5.@PathVariable
@PathVariable注解用来获取url中的数据,以下为具体的使用方法,
在HelloController控制器中添加方法getBook,通过占位符传递bookId:
@RequestMapping(value = \"/getBook/{bookId}\", method = RequestMethod.GET)
public Book getBook(@PathVariable Integer bookId) {
Book book = null;
List<Book> books = new ArrayList<>();
try {
Book book1 = new Book(1, \"平凡的世界\", \"路遥\", \"2010-01-01\");
Book book2 = new Book(2, \"人生\", \"路遥\", \"2011-01-01\");
books.add(book1);
books.add(book2);
book = books.get(bookId - 1);
} catch (ParseException e) {
e.printStackTrace();
}
return book;
}
运行项目,在浏览器中访问http://localhost:8080/hello/getBook/1,结果如下:
// 20190424145348
// http://localhost:8080/hello/getBook/1
{
\"bookId\": 1,
\"bookName\": \"平凡的世界\",
\"bookAuthor\": \"路遥\",
\"purchaseDate\": \"2009-12-31 16:00:00\"
}
注意:占位符里的名称必须和参数名完全一致,区分大小写,否则访问会报500错误。
如果想不一致,可以写成如下方式:
@RequestMapping(value = \"/getBook/{bookId}\", method = RequestMethod.GET)
public Book getBook(@PathVariable(\"bookId\") Integer bookIndex) {
......
}
这种方式也要求,PathVariable的value属性值必须与占位符里的名称完全一致。
好了,本篇文章就先讲解这么多,其它注解后续再单独发布文章讲解。
6.源码地址
原文地址:Spring Boot入门(四):开发Web Api接口常用注解总结
源码地址:https://github.com/zwwhnly/springbootdemo.git
欢迎大家下载,有问题可以多多交流。
7.参考链接
用Spring Boot开发一个web API 接口返回数据
SpringBoot 中常用注解@Controller/@RestController/@RequestMapping介绍