在Maven插件的幫助下,VSCode寫Java其實非常方便。這一講我們介紹如何借助maven用VScode搭建Hadoop開發環境。
1.Java環境安裝
首先我們需要搭建好Java開發環境。我們需要從網站 https://www.oracle.com/java/technologies/downloads/ 下載指定版本的Java壓縮包或安裝包。壓縮包需要解壓到機器的指定目錄,安裝包直接傻瓜式安裝即可。我這里下載的是Java17的MacOS安裝包,運行后它默認給我安裝在了/Library/Java/JavaVirtualMachines/temurin-17.jdk/
目錄下。
然后配置環境變量,Mac用戶在~/.zshrc
中添加:
export JAVA_HOME=/Library/Java/JavaVirtualMachines/temurin-17.jdk/Contents/Home
然后source ~/.zshrc
即可(Linux用戶我沒記錯的話應該是~/.bashrc
文件)。
可以運行java -version
命令查看當前機器的Java版本。
(base) lonelyprince7@lonelyprince7deMacBook-Pro ~ % java -version
openjdk version "17" 2021-09-14
OpenJDK Runtime Environment Temurin-17+35 (build 17+35)
OpenJDK 64-Bit Server VM Temurin-17+35 (build 17+35, mixed mode)
然后讀者需要在VSCode中安裝以下Java插件:
其中需要注意,Maven for Java插件是用來構建Java大型項目的(也就是說不只是使用JRE內部的包,而且使用外包的JDK包。內部的包用java
命令編譯的時候就會自動幫我們導入,但外部的包要稍微復雜一些,最簡單的方式就是使用maven工具了)。
安裝Maven
如果你是Mac系統且安裝了homebrew,可以直接下列命令運行安裝
brew install maven
你也可以前往Maven官網 https://maven.apache.org/download.cgi 下載並解壓到自定義目錄。
安裝完后記得配置環境變量:
export M2_HOME=/opt/homebrew/Cellar/maven/3.8.2/libexec
export PATH=${PATH}:${M2_HOME}/bin
此處/opt/homebrew/Cellar/maven/3.8.2/libexec
是我的maven安裝位置,修改成你實際的自定義目錄即可。
然后source ~/.zshrc
即可(同樣,Linux用戶應該是~/.bashrc
文件)。
運行mvn -version
可以查看maven版本。
(base) orion-orion@MacBook-Pro libexec % mvn -version
Apache Maven 3.8.2 (3599d3414f046de2324203b78ddcf9b5e4388aa0)
Maven home: /opt/homebrew/Cellar/maven/3.8.2/libexec
Java version: temurin-17, vendor: Oracle Corporation, runtime: /Library/Java/JavaVirtualMachines/temurin-17.jdk/Contents/Home
Default locale: zh_CN_#Hans, platform encoding: UTF-8
OS name: "mac os x", version: "12.3.1", arch: "aarch64", family: "mac"
3.新建Maven項目
首先,用VSCode打開一個存放用於項目的目錄(在我電腦上是 "/Users/lonelyprince7/Documents/LocalCode/Hadoop-MapReduce"
),然后在右鍵菜單中選擇從Maven原型中創建新項目。

然后從下拉選單中選擇“maven-archetype-quickstart”。

然后隨便選擇一個版本即可。



然后我們的工程目錄就選擇 "/Users/lonelyprince7/Documents/LocalCode/Hadoop-MapReduce"
就行。

之后VSCode會提示是否跳轉到"hello_world"工程的目錄,選擇“是”,然后就退跳轉到該目錄。
進入該目錄后,我們會發現控制台正在初始化Maven配置,有以下打印輸出:
其中,會跳出一些選項讓我們選擇,我們只需要全部按回車選擇默認值即可。
最后,我們看到項目"hello_world"成功創建,項目目錄如下:
3.進行測試
我們可以看到App.java已經為我們生成,為如下內容:
package com.orion;
/**
* Hello world!
*
*/
public class App
{
public static void main( String[] args )
{
System.out.println( "Hello World!" );
}
}
pom.xml只引入了最基本的junit依賴包,並配置了一些基本的Maven項目初始化的內容:
<?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>com.orion</groupId>
<artifactId>hello_world</artifactId>
<version>1.0-SNAPSHOT</version>
<name>hello_world</name>
<!-- FIXME change it to the project's website -->
<url>http://www.example.com</url>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<maven.compiler.source>1.7</maven.compiler.source>
<maven.compiler.target>1.7</maven.compiler.target>
</properties>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.11</version>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<pluginManagement><!-- lock down plugins versions to avoid using Maven defaults (may be moved to parent pom) -->
<plugins>
<!-- clean lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#clean_Lifecycle -->
<plugin>
<artifactId>maven-clean-plugin</artifactId>
<version>3.1.0</version>
</plugin>
<!-- default lifecycle, jar packaging: see https://maven.apache.org/ref/current/maven-core/default-bindings.html#Plugin_bindings_for_jar_packaging -->
<plugin>
<artifactId>maven-resources-plugin</artifactId>
<version>3.0.2</version>
</plugin>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.8.0</version>
</plugin>
<plugin>
<artifactId>maven-surefire-plugin</artifactId>
<version>2.22.1</version>
</plugin>
<plugin>
<artifactId>maven-jar-plugin</artifactId>
<version>3.0.2</version>
</plugin>
<plugin>
<artifactId>maven-install-plugin</artifactId>
<version>2.5.2</version>
</plugin>
<plugin>
<artifactId>maven-deploy-plugin</artifactId>
<version>2.8.2</version>
</plugin>
<!-- site lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#site_Lifecycle -->
<plugin>
<artifactId>maven-site-plugin</artifactId>
<version>3.7.1</version>
</plugin>
<plugin>
<artifactId>maven-project-info-reports-plugin</artifactId>
<version>3.0.0</version>
</plugin>
</plugins>
</pluginManagement>
</build>
</project>
選中App.java
文件按F5
進行編譯並運行,看到控制台成功打印Hello World!
:
(base) lonelyprince7@lonelyprince7deMacBook-Pro hello_world % /usr/bin/env /Library/Java/JavaVirtualMachines/temurin-17.jdk/Contents/Home/bin/java -agentlib:jdwp=transport=dt_socket,server=n,suspend=y,address=localhost:50684 -XX:+ShowCodeDetailsInExceptionMessages -cp /Users/lonelyprince7/Documents/LocalCode/Hadoop-MapReduce/hello_world/target/classes com.orion.App
Hello World!
我們接下來試試用Maven導入Hadoop依賴。我們只需要在pom.xml依賴項就行。相關的依賴項的名稱和版本號我們可以在Maven倉庫的官網 https://mvnrepository.com/ 進行查詢,比如我們可以查詢到Hadoop-common(3.3.1)版本的依賴項如下:

一般來說,Hadoop項目需要引入hadoop-common、hadoop-hdfs、hadoop-client、hadoop-yarn-api這幾個api,我們需要將下列標簽加入<dependencies> <dependencies/>
之間,也即:
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.11</version>
<scope>test</scope>
</dependency>
<!-- 導入hadoop依賴環境 -->
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-common</artifactId>
<version>3.3.1</version>
</dependency>
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-hdfs</artifactId>
<version>3.3.1</version>
</dependency>
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-mapreduce-client-core</artifactId>
<version>3.3.1</version>
</dependency>
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-client</artifactId>
<version>3.3.1</version>
</dependency>
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-yarn-api</artifactId>
<version>3.3.1</version>
</dependency>
</dependencies>
但是聰明的逆可能已經注意到了,這樣版本號就完全屬於“硬編碼”了。后期我要修改hadoop的版本號,只能把上面的挨個修改,非常麻煩。好在我們在<properties></properties>
標簽之間先集中定義好一些后面要使用的常量(比如版本號),后面再使用${變量名}
的形式來引用即可。如我們將hadoop的版本號hadoop.version
追加到<properties></properties>
標簽之間:
<!-- 集中定義版本號 -->
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<maven.compiler.source>1.7</maven.compiler.source>
<maven.compiler.target>1.7</maven.compiler.target>
<hadoop.version>3.3.1</hadoop.version> <!--這里追加hadoop版本號-->
</properties>
然后后面我們就可以使用${hadoop.version}
來替代前面頻繁出現的3.3.1
了。
最后給出我們完整的pom.xml文件:
<?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>com.orion</groupId>
<artifactId>hello_world</artifactId>
<version>1.0-SNAPSHOT</version>
<name>hello_world</name>
<!-- FIXME change it to the project's website -->
<url>http://www.example.com</url>
<!-- 集中定義版本號 -->
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<maven.compiler.source>1.7</maven.compiler.source>
<maven.compiler.target>1.7</maven.compiler.target>
<hadoop.version>3.3.1</hadoop.version> <!--這里追加hadoop版本號-->
</properties>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.11</version>
<scope>test</scope>
</dependency>
<!-- 導入hadoop依賴環境 -->
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-common</artifactId>
<version>${hadoop.version}</version>
</dependency>
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-hdfs</artifactId>
<version>${hadoop.version}</version>
</dependency>
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-mapreduce-client-core</artifactId>
<version>${hadoop.version}</version>
</dependency>
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-client</artifactId>
<version>${hadoop.version}</version>
</dependency>
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-yarn-api</artifactId>
<version>${hadoop.version}</version>
</dependency>
</dependencies>
</dependencies>
<build>
<pluginManagement><!-- lock down plugins versions to avoid using Maven defaults (may be moved to parent pom) -->
<plugins>
<!-- clean lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#clean_Lifecycle -->
<plugin>
<artifactId>maven-clean-plugin</artifactId>
<version>3.1.0</version>
</plugin>
<!-- default lifecycle, jar packaging: see https://maven.apache.org/ref/current/maven-core/default-bindings.html#Plugin_bindings_for_jar_packaging -->
<plugin>
<artifactId>maven-resources-plugin</artifactId>
<version>3.0.2</version>
</plugin>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.8.0</version>
</plugin>
<plugin>
<artifactId>maven-surefire-plugin</artifactId>
<version>2.22.1</version>
</plugin>
<plugin>
<artifactId>maven-jar-plugin</artifactId>
<version>3.0.2</version>
</plugin>
<plugin>
<artifactId>maven-install-plugin</artifactId>
<version>2.5.2</version>
</plugin>
<plugin>
<artifactId>maven-deploy-plugin</artifactId>
<version>2.8.2</version>
</plugin>
<!-- site lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#site_Lifecycle -->
<plugin>
<artifactId>maven-site-plugin</artifactId>
<version>3.7.1</version>
</plugin>
<plugin>
<artifactId>maven-project-info-reports-plugin</artifactId>
<version>3.0.0</version>
</plugin>
</plugins>
</pluginManagement>
</build>s
</project>
按ctrl/command+s
保存,項目會對pom.xml
重新解析,導入我們添加進入的包。
最后我們嘗試在App.java
中導入hadoop相關的包:
package com.orion;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
/**
* Hello world!
*
*/
public class App
{
public static void main( String[] args )
{
System.out.println( "Hello World!" );
}
}
按'F5'重新編譯運行,成功打印輸出Hello World!
,說明我們的包導入成功。
(base) lonelyprince7@lonelyprince7deMacBook-Pro hello_world % /usr/bin/env /Library/Java/JavaVirtualMachines/temurin-17.jdk/Contents/Home/bin/java -agentlib:jdwp=transport=dt_socket,server=n,suspend=y,address=localhost:54181 --enable-preview -XX:+ShowCodeDetailsInExceptionMessages -cp "/Users/lonelyprince7/Library/Application Support/Code/User/workspaceStorage/fe34994f622cdbfbf60e8ed045c6bde3/redhat.java/jdt_ws/jdt.ls-java-project/bin" com.orion.App
Hello World!
注意,如果報錯org.apache.hadoop.fs.FileSystem cant be resolved
這種錯誤,則需要先清空項目緩存,然后再重新編譯運行。
至此,我們已經成功用VScode+Maven創建好一個Hadoop的開發環境。在Hadoop編程中,最基本的一種分布式編程范式即MapReduce編程。在后面我們會借由“WordCount”(詞頻統計)這個MapReduce編程的入門項來講解Hadoop中MapReduce編程的基本語法,敬請繼續關注。