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使用 Java Springboot 开发 Restful API 接口 - 2021版

- by zhaiduo.com - 标签： JavaSpringbootRestful

都2021年了，对初学Java的同学来说，起点要高，高度要够。

I、首先，我们看看开发配置环境：
  1. IDE: 我们使用VSCode
  2. Java SDK 1.8+

    • 检查是否安装Java 1.8: java -version

    • 下载 Spring Boot CLI，解压到目录，把目录命令行路径加入Path，检测是否安装成功：spring --version

  3. 安装Maven 3+ 或者 Gradle 4+
    • 下载 Maven 3.6.3，解压到目录，把目录命令行路径加入Path，检测是否安装成功：mvn --version
II、其次，脚手架生成项目，我们需要去 https://start.spring.io/ 下载一个初始化项目：

初始化项目

选择依赖：

  1. Spring Web - 包含Spring MVC框架和内嵌Tomcat服务器
  2. Spring Data JPA - 数据持久化接口
  3. Spring Boot DevTools - 开发工具
  4. MySQL Driver - JDBC 驱动器

点击Generate生成按钮，生成初始化项目 demoRestful.zip, 解压。

III、或者手动生成项目，新建目录firstDemo
  1. 新建pom.xml，并且当前目录下运行：mvn package
1<?xml version="1.0" encoding="UTF-8"?>
2<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
3    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
4    <modelVersion>4.0.0</modelVersion>
5
6    <groupId>com.example</groupId>
7    <artifactId>myproject</artifactId>
8    <version>0.0.1-SNAPSHOT</version>
9
10    <parent>
11        <groupId>org.springframework.boot</groupId>
12        <artifactId>spring-boot-starter-parent</artifactId>
13        <version>2.4.3</version>
14    </parent>
15
16    <description/>
17    <developers>
18        <developer/>
19    </developers>
20    <licenses>
21        <license/>
22    </licenses>
23    <scm>
24        <url/>
25    </scm>
26    <url/>
27
28    <!-- Additional lines to be added here... -->
29    <dependencies>
30        <dependency>
31            <groupId>org.springframework.boot</groupId>
32            <artifactId>spring-boot-starter-web</artifactId>
33        </dependency>
34    </dependencies>
35
36</project>
  1. 查看依赖：mvn dependency:tree
  2. 新建目录 src/main/java ，在 java 目录下新建 Example.java
1import org.springframework.boot.*;
2import org.springframework.boot.autoconfigure.*;
3import org.springframework.web.bind.annotation.*;
4
5@RestController //表示要处理web请求
6@EnableAutoConfiguration //表示自动配置Spring
7public class Example {
8
9    @RequestMapping("/") //表示请求的url相对地址
10    String home() {
11        return "Hello World!";
12    }
13
14    //入口函数
15    public static void main(String[] args) {
16        SpringApplication.run(Example.class, args);
17    }
18
19}
  1. 回到项目根目录 firstDemo，运行：mvn spring-boot:run （限制内存：export MAVEN_OPTS=-Xmx1024m）
1[INFO] Attaching agents: []
2
3  .   ____          _            __ _ _
4 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
5( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
6 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
7  '  |____| .__|_| |_|_| |_\__, | / / / /
8 =========|_|==============|___/=/_/_/_/
9 :: Spring Boot ::                (v2.4.3)
  1. 启动成功后即可在浏览器访问：http://localhost:8080/
1Hello World!
发布代码（可执行 jar 文件）
  1. pom.xml 中 <dependencies > 后添加编译配置:
1<build>
2    <plugins>
3        <plugin>
4            <groupId>org.springframework.boot</groupId>
5            <artifactId>spring-boot-maven-plugin</artifactId>
6        </plugin>
7    </plugins>
8</build>
  1. 根目录 firstDemo，运行：mvn package，你会发现新生成了一个目录 target
  2. 根目录 firstDemo，启动jar包：java -jar target/myproject-0.0.1-SNAPSHOT.jar (支持远程调试：java -Xdebug -Xrunjdwp:server=y,transport=dt_socket,address=8000,suspend=n
    -jar target/myproject-0.0.1-SNAPSHOT.jar)
  3. 启动成功后即可在浏览器访问：http://localhost:8080/
1Hello World!
RESTful 接口
  1. 进入之前解压的 demoRestful 目录, 编辑 application.properties文件，加入：
1spring.autoconfigure.exclude=org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration
  1. 回到项目根目录 demoRestful，运行：mvn spring-boot:run
1[INFO] Attaching agents: []
2
3  .   ____          _            __ _ _
4 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
5( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
6 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
7  '  |____| .__|_| |_|_| |_\__, | / / / /
8 =========|_|==============|___/=/_/_/_/
9 :: Spring Boot ::                (v2.4.3)
  1. 启动成功后即可在浏览器访问：http://localhost:8080/
1Whitelabel Error Page
2This application has no explicit mapping for /error, so you are seeing this as a fallback.
3
4Sat Feb 27 20:46:29 CST 2021
5There was an unexpected error (type=Not Found, status=404).
6No message available
  1. 回到项目根目录 demoRestful，添加Greeting.java和GreetingController.java：
1//Greeting.java
2package com.zhaiduo.demoRestful;
3
4public class Greeting {
5
6	private final long id;
7	private final String content;
8
9	public Greeting(long id, String content) {
10		this.id = id;
11		this.content = content;
12	}
13
14	public long getId() {
15		return id;
16	}
17
18	public String getContent() {
19		return content;
20	}
21}
22

1//GreetingController.java
2package com.zhaiduo.demoRestful;
3
4import java.util.concurrent.atomic.AtomicLong;
5
6import org.springframework.web.bind.annotation.GetMapping;
7import org.springframework.web.bind.annotation.RequestParam;
8import org.springframework.web.bind.annotation.RestController;
9
10@RestController
11public class GreetingController {
12
13	private static final String template = "Hello, %s!";
14	private final AtomicLong counter = new AtomicLong();
15
16	@GetMapping("/greeting")
17	public Greeting greeting(@RequestParam(value = "name", defaultValue = "World") String name) {
18		return new Greeting(counter.incrementAndGet(), String.format(template, name));
19	}
20}
21
  1. 启动成功后即可在浏览器访问：http://localhost:8080/greeting?name=$xxx
1{
2id: 3,
3content: "Hello, $xxx!"
4}
Springboot 快速测试代码
1@RestController
2class ThisWillActuallyRun {
3
4    @RequestMapping("/")
5    String home() {
6        "Hello World!"
7    }
8
9}
10//spring run installTest.groovy
11//localhost:8080
常见问题
  1. 运行 spring run installTest.groovy 报错：Failed to collect dependencies at org.springframework.boot
1再次运行即可
  1. [ERROR] No plugin found for prefix 'spring-boot' in the current project
1确保命令运行的目录有pom.xml文件
  1. DataSourceProperties$DataSourceBeanCreationException: Failed to determine a suitable driver class https://www.baeldung.com/spring-boot-failed-to-configure-data-source
参考网址：
  • https://docs.spring.io/spring-boot/docs/current/reference/html/getting-started.html#getting-started-introducing-spring-boot
  • https://docs.spring.io/spring-boot/docs/current/reference/html/using-spring-boot.html#using-boot
  • https://spring.io/guides/gs/rest-service/
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