服務端程序本質上也只是個Java程序，它接收客戶端的輸入，然后將計算處理后的返回值返回給客戶端。下面我們就以這個思路開始Java后端之旅吧。

引用Spring Boot庫

處理HTTP請求之類的事情，我們需要庫的幫助。所以第一步我們就把Spring Boot引入進來。
不需要任何工具，我們使用maven來管理庫依賴，這樣我們只要寫一個pom.xml就好了。我們先寫一個最簡的pom.xml。主要是定義groupId，比如是我司，還有artifactId，就是應用的具體名字：

<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><groupId>cn.alios.system.service.prefix</groupId><artifactId>Prefix</artifactId><version>1.0.0-SNAPSHOT</version></project>

添加父引用

類似于類的繼承，我們不是從頭開發，而是繼承Spring Boot Starter框架。添加parent的內容如下：

<parent><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-parent</artifactId><version>2.1.2.RELEASE</version></parent>

2.1.2是本文寫作時，Spring Boot的最新版本。

增加依賴

為了自動下載庫，我們將需要的幾個庫添加到pom.xml中的依賴項中。這樣maven就可以幫我們從倉庫中下載最新的庫代碼。
我們需要AOP和Web兩個包，用全名是spring-boot-starter-aop和spring-boot-starter-web:

<dependencies><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-aop</artifactId></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency></dependencies>

引用插件

Spring Boot還提供了插件，我們也將其引用進來：

<build><plugins><plugin><groupId>org.springframework.boot</groupId><artifactId>spring-boot-maven-plugin</artifactId></plugin></plugins></build>

主函數

庫引用完了，我們就寫一個主程序吧。按照慣例，我們將其保存在src/main/java目錄下：

package cn.alios.system.service.prefix;import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.ResponseBody;@SpringBootApplication @RequestMapping("/") public class Prefix {@RequestMapping("/")@ResponseBodypublic String home(){return "Hello, Java Web World!";}public static void main(String[] args) throws Exception{SpringApplication.run(Prefix.class,args);} }

編譯

下面我們用mvn package命令來編譯生成可運行的jar包：

mvn package

輸出類似于下面這樣：

[INFO] Scanning for projects... [INFO] [INFO] ---------------< cn.alios.system.service.prefix:Prefix >---------------- [INFO] Building Prefix 1.0.0-SNAPSHOT [INFO] --------------------------------[ jar ]--------------------------------- [INFO] [INFO] --- maven-resources-plugin:3.1.0:resources (default-resources) @ Prefix --- [INFO] Using 'UTF-8' encoding to copy filtered resources. [INFO] Copying 0 resource [INFO] Copying 0 resource [INFO] [INFO] --- maven-compiler-plugin:3.8.0:compile (default-compile) @ Prefix --- [INFO] Changes detected - recompiling the module! [INFO] Compiling 1 source file to /Users/ziyingliuziying/working/gitlab/Prefix/target/classes [INFO] [INFO] --- maven-resources-plugin:3.1.0:testResources (default-testResources) @ Prefix --- [INFO] Using 'UTF-8' encoding to copy filtered resources. [INFO] skip non existing resourceDirectory /Users/ziyingliuziying/working/gitlab/Prefix/src/test/resources [INFO] [INFO] --- maven-compiler-plugin:3.8.0:testCompile (default-testCompile) @ Prefix --- [INFO] Nothing to compile - all classes are up to date [INFO] [INFO] --- maven-surefire-plugin:2.22.1:test (default-test) @ Prefix --- [INFO] No tests to run. [INFO] [INFO] --- maven-jar-plugin:3.1.1:jar (default-jar) @ Prefix --- [INFO] Building jar: /Users/ziyingliuziying/working/gitlab/Prefix/target/Prefix-1.0.0-SNAPSHOT.jar [INFO] [INFO] --- spring-boot-maven-plugin:2.1.2.RELEASE:repackage (repackage) @ Prefix --- [INFO] Replacing main artifact with repackaged archive [INFO] ------------------------------------------------------------------------ [INFO] BUILD SUCCESS [INFO] ------------------------------------------------------------------------ [INFO] Total time: 2.462 s [INFO] Finished at: 2019-01-31T16:53:48+08:00 [INFO] ------------------------------------------------------------------------

最后生成的包是target/Prefix-1.0.0-SNAPSHOT.jar。

運行

調用java -jar target/Prefix-1.0.0-SNAPSHOT.jar命令，運行這個Java程序，輸出如下：

. ____ _ __ _ _/\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \ ( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \\\/ ___)| |_)| | | | | || (_| | ) ) ) )' |____| .__|_| |_|_| |_\__, | / / / /=========|_|==============|___/=/_/_/_/:: Spring Boot :: (v2.1.2.RELEASE)2019-01-31 16:59:43.144 INFO 95879 --- [ main] cn.alios.system.service.prefix.Prefix : Starting Prefix v1.0.0-SNAPSHOT on ziyingliuziyingdeMacBook-Pro.local with PID 95879 (/Users/ziyingliuziying/working/gitlab/Prefix/target/Prefix-1.0.0-SNAPSHOT.jar started by ziyingliuziying in /Users/ziyingliuziying/working/gitlab/Prefix) 2019-01-31 16:59:43.148 INFO 95879 --- [ main] cn.alios.system.service.prefix.Prefix : No active profile set, falling back to default profiles: default 2019-01-31 16:59:44.289 INFO 95879 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8080 (http) 2019-01-31 16:59:44.325 INFO 95879 --- [ main] o.apache.catalina.core.StandardService : Starting service [Tomcat] 2019-01-31 16:59:44.325 INFO 95879 --- [ main] org.apache.catalina.core.StandardEngine : Starting Servlet engine: [Apache Tomcat/9.0.14] 2019-01-31 16:59:44.347 INFO 95879 --- [ main] o.a.catalina.core.AprLifecycleListener : The APR based Apache Tomcat Native library which allows optimal performance in production environments was not found on the java.library.path: [/Users/ziyingliuziying/Library/Java/Extensions:/Library/Java/Extensions:/Network/Library/Java/Extensions:/System/Library/Java/Extensions:/usr/lib/java:.] 2019-01-31 16:59:44.435 INFO 95879 --- [ main] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext 2019-01-31 16:59:44.435 INFO 95879 --- [ main] o.s.web.context.ContextLoader : Root WebApplicationContext: initialization completed in 1234 ms 2019-01-31 16:59:44.665 INFO 95879 --- [ main] o.s.s.concurrent.ThreadPoolTaskExecutor : Initializing ExecutorService 'applicationTaskExecutor' 2019-01-31 16:59:44.886 INFO 95879 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path '' 2019-01-31 16:59:44.889 INFO 95879 --- [ main] cn.alios.system.service.prefix.Prefix : Started Prefix in 2.161 seconds (JVM running for 2.561)

我們可以看到，啟動了一個9.0.14版本的Apache Tomcat服務器，在8080端口上監聽。

我們打開瀏覽器，訪問http://127.0.0.1:8080/，可以看到『Hello, Java Web World!』這個字符串被顯示出來。

再寫一個Controller

在主函數里面可以處理請求，那么再其它類里面該如何做呢？我們通過寫@Controller注解，加上@RequestMapping來指定路徑，就可以了。
我們來寫個例子：

package cn.alios.system.service.prefix.controller;import org.springframework.stereotype.Controller; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.ResponseBody;@Controller @RequestMapping("/test") public class TestController {@RequestMapping("/")@ResponseBodypublic String test(){return "Test Controller!";} }

還是mvn package，然后java -jar java -jar target/Prefix-1.0.0-SNAPSHOT.jar。
在瀏覽器里試下http://127.0.0.1:8080/test/，顯示：『Test Controller!』
大功告成！現在整個從接收輸入到顯示輸出的通道已經打通，是不是很easy?

?

原文鏈接
本文為云棲社區原創內容，未經允許不得轉載。

總結

以上是生活随笔為你收集整理的全民学后端快餐教程(1) - 只不过是写个Java程序的全部內容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網站內容還不錯，歡迎將生活随笔推薦給好友。