https://spring.io/projects/spring-framework
Spring Framework 为基于 Java 的现代企业应用程序 （在任何类型的部署平台上）提供了全面的编程和配置模型。
Spring 的一个关键要素是应用程序级别的基础设施支持：Spring 侧重于企业应用程序的"管道"，以便团队可以专注于应用程序级的业务逻辑，而无需与特定的部署环境进行不必要的联系。
特性
- 核心技术： 依赖项注入、事件、资源、i18n、验证、数据绑定、类型转换、SpEL、AOP。
- 测试：模拟对象，测试上下文框架，Spring MVC 测试。
WebTestClient
- 数据访问： 事务， Dao 支持， Jdbc， ORM（Hibernate，Mybatis（Sql映射））。
- Spring MVC和Spring WebFlux Web 框架。
- 集成： 远程处理， JMS， JCA， JMX， 电子邮件， 任务， 计划， 缓存。
- 语言： Java, Kotlin, Groovy， 等动态语言。
Spring Core Technologies
https://docs.spring.io/spring-framework/docs/current/reference/html/core.html
Spring框架核心技术中最重要的是 Spring 框架的控制反转 （IoC） 容器以及面向切面编程 （AOP） 技术。
SpringBoot
https://spring.io/projects/spring-boot
Spring Boot 可轻松创建独立的、生产级 Spring 应用程序，您可以"直接运行(java jar)"，而无需提前准备例如Tomcat应用容器服务器。
Spring Boot 启动应用程序只需要最少的Spring相关配置，贯彻“约定大于配置”的理念。
如果您要查找有关特定版本的信息，或有关如何从早期版本升级的说明，请查看项目发行说明部分在我们的维基上。
特性
- 创建独立的Spring应用
- 直接嵌入 Tomcat、Jetty 或底图（Undertow，无需部署 WAR 文件）
- 提供有意见的"启动器"依赖关系，以简化生成配置
- 尽可能自动配置Spring和第三方库
- 提供支持生产所需功能，如指标、健康检查和外部配置
- 绝对没有生成代码，极大减少 XML 配置要求
快速开始
RESTful Web Service
https://spring.io/guides/gs/rest-service/
This guide walks you through the process of creating a “Hello, World” RESTful web service with Spring.
What You Will Build
You will build a service that will accept HTTP GET requests at http://localhost:8080/greeting.
It will respond with a JSON representation of a greeting, as the following listing shows:
{"id":1,"content":"Hello, World!"}
You can customize the greeting with an optional name parameter in the query string, as the following listing shows:
http://localhost:8080/greeting?name=User
The name parameter value overrides the default value of World and is reflected in the response, as the following listing shows:
{"id":1,"content":"Hello, User!"}
What You Need
- About 15 minutes
- A favorite text editor or IDE
- JDK 1.8 or later
- Gradle 4+ or Maven 3.2+
- You can also import the code straight into your IDE:
How to complete this guide
Like most Spring Getting Started guides, you can start from scratch and complete each step or you can bypass basic setup steps that are already familiar to you. Either way, you end up with working code.
To start from scratch, move on to Starting with Spring Initializr.
To skip the basics, do the following:
When you finish, you can check your results against the code in gs-rest-service/complete.
Starting with Spring Initializr
For all Spring applications, you should start with the Spring Initializr. The Initializr offers a fast way to pull in all the dependencies you need for an application and does a lot of the setup for you. This example needs only the Spring Web dependency.
The following listing shows the pom.xml file that is created when you choose Maven:
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.3.0.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>com.example</groupId>
<artifactId>rest-service</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>rest-service</name>
<description>Demo project for Spring Boot</description>
<properties>
<java.version>1.8</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-actuator</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
<exclusions>
<exclusion>
<groupId>org.junit.vintage</groupId>
<artifactId>junit-vintage-engine</artifactId>
</exclusion>
</exclusions>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>
The following listing shows the build.gradle file that is created when you choose Gradle:
plugins {
id 'org.springframework.boot' version '2.3.2.RELEASE'
id 'io.spring.dependency-management' version '1.0.8.RELEASE'
id 'java'
}
group = 'com.example'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = '1.8'
repositories {
mavenCentral()
}
dependencies {
implementation 'org.springframework.boot:spring-boot-starter-web'
testImplementation('org.springframework.boot:spring-boot-starter-test') {
exclude group: 'org.junit.vintage', module: 'junit-vintage-engine'
}
}
test {
useJUnitPlatform()
}
Create a Resource Representation Class
Now that you have set up the project and build system, you can create your web service.
Begin the process by thinking about service interactions.
The service will handle GET requests for /greeting, optionally with a name parameter in the query string. The GET request should return a 200 OK response with JSON in the body that represents a greeting. It should resemble the following output:
{
"id": 1,
"content": "Hello, World!"
}
The id field is a unique identifier for the greeting, and content is the textual representation of the greeting.
To model the greeting representation, create a resource representation class. To do so, provide a plain old Java object with fields, constructors, and accessors for the id and content data, as the following listing (from src/main/java/com/example/restservice/Greeting.java) shows:
package com.example.restservice;
public class Greeting {
private final long id;
private final String content;
public Greeting(long id, String content) {
this.id = id;
this.content = content;
}
public long getId() {
return id;
}
public String getContent() {
return content;
}
}
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This application uses the Jackson JSON library to automatically marshal instances of type Greeting into JSON. Jackson is included by default by the web starter. |
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Create a Resource Controller
In Spring’s approach to building RESTful web services, HTTP requests are handled by a controller. These components are identified by the @RestController annotation, and the GreetingController shown in the following listing (from src/main/java/com/example/restservice/GreetingController.java) handles GET requests for /greeting by returning a new instance of the Greeting class:
package com.example.restservice;
import java.util.concurrent.atomic.AtomicLong;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;
@RestController
public class GreetingController {
private static final String template = "Hello, %s!";
private final AtomicLong counter = new AtomicLong();
@GetMapping("/greeting")
public Greeting greeting(@RequestParam(value = "name", defaultValue = "World") String name) {
return new Greeting(counter.incrementAndGet(), String.format(template, name));
}
}
This controller is concise and simple, but there is plenty going on under the hood. We break it down step by step.
The @GetMapping annotation ensures that HTTP GET requests to /greeting are mapped to the greeting() method.
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There are companion annotations for other HTTP verbs (e.g. @PostMapping for POST). There is also a @RequestMapping annotation that they all derive from, and can serve as a synonym (e.g. @RequestMapping(method=GET)). |
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@RequestParam binds the value of the query string parameter name into the name parameter of the greeting() method. If the name parameter is absent in the request, the defaultValue of World is used.
The implementation of the method body creates and returns a new Greeting object with id and content attributes based on the next value from the counter and formats the given name by using the greeting template.
A key difference between a traditional MVC controller and the RESTful web service controller shown earlier is the way that the HTTP response body is created. Rather than relying on a view technology to perform server-side rendering of the greeting data to HTML, this RESTful web service controller populates and returns a Greeting object. The object data will be written directly to the HTTP response as JSON.
This code uses Spring @RestController annotation, which marks the class as a controller where every method returns a domain object instead of a view. It is shorthand for including both @Controller and @ResponseBody.
The Greeting object must be converted to JSON. Thanks to Spring’s HTTP message converter support, you need not do this conversion manually. Because Jackson 2 is on the classpath, Spring’s MappingJackson2HttpMessageConverter is automatically chosen to convert the Greeting instance to JSON.
@SpringBootApplication is a convenience annotation that adds all of the following:
@Configuration: Tags the class as a source of bean definitions for the application context.@EnableAutoConfiguration: Tells Spring Boot to start adding beans based on classpath settings, other beans, and various property settings. For example, if spring-webmvc is on the classpath, this annotation flags the application as a web application and activates key behaviors, such as setting up a DispatcherServlet.@ComponentScan: Tells Spring to look for other components, configurations, and services in the com/example package, letting it find the controllers.
The main() method uses Spring Boot’s SpringApplication.run() method to launch an application. Did you notice that there was not a single line of XML? There is no web.xml file, either. This web application is 100% pure Java and you did not have to deal with configuring any plumbing or infrastructure.
Build an executable JAR
You can run the application from the command line with Gradle or Maven. You can also build a single executable JAR file that contains all the necessary dependencies, classes, and resources and run that. Building an executable jar makes it easy to ship, version, and deploy the service as an application throughout the development lifecycle, across different environments, and so forth.
If you use Gradle, you can run the application by using ./gradlew bootRun. Alternatively, you can build the JAR file by using ./gradlew build and then run the JAR file, as follows:
java -jar build/libs/gs-rest-service-0.1.0.jar
If you use Maven, you can run the application by using ./mvnw spring-boot:run. Alternatively, you can build the JAR file with ./mvnw clean package and then run the JAR file, as follows:
java -jar target/gs-rest-service-0.1.0.jar
Logging output is displayed. The service should be up and running within a few seconds.
Test the Service
Now that the service is up, visit http://localhost:8080/greeting, where you should see:
{"id":1,"content":"Hello, World!"}
Provide a name query string parameter by visiting http://localhost:8080/greeting?name=User. Notice how the value of the content attribute changes from Hello, World! to Hello, User!, as the following listing shows:
{"id":2,"content":"Hello, User!"}
This change demonstrates that the @RequestParam arrangement in GreetingController is working as expected. The name parameter has been given a default value of World but can be explicitly overridden through the query string.
Notice also how the id attribute has changed from 1 to 2. This proves that you are working against the same GreetingController instance across multiple requests and that its counter field is being incremented on each call as expected.
Summary
Congratulations! You have just developed a RESTful web service with Spring.
See Also
The following guides may also be helpful:
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