maven从入门到精通 第三章 Maven中形成web对Java工程的依赖

一 war永远依赖于jar

从来只有war包中含有jar包，而没有jar包中含有war包
web工程依赖的java工程，就是jar包，这个jar包经过自动化部署后,会放在web工程的web-inf/lib目录下

1. 在web工程的项目2中,加入项目1的路径依赖

在 pro02-maven-web 工程的 pom.xml 中，找到 dependencies 标签，在 dependencies 标签中做如下配置

<dependency>
<!--
通过指定被依赖工程的坐标完成依赖
-->
  <groupId>com.xyt.maven</groupId>
  <artifactId>pro01-maven-java</artifactId>
  <version>1.0-SNAPSHOT</version>
  <scope>compiler</scope>
 
</dependency>

2 在web工程中，加入测试代码

证明在Web工程中可以使用Java工程中创建的那个类：Calculator

2.1 创建目录

mkdir src\test\java\com\xyt\maven

2.2 确认依赖junit

<dependency>
  <groupId>junit</groupId>
  <artifactId>junit</artifactId>
  <version>4.12</version>
  <scope>test</scope>
</dependency>

2.3创建测试类

2.4 运行测试

mvn test

2.5 打包

D:\maven_workspace\spaceVideo\pro02-maven-web>mvn package
[INFO] Scanning for projects...
[INFO]
[INFO] -------------------< com.xyt.maven:pro02-maven-web >--------------------
[INFO] Building pro02-maven-web Maven Webapp 1.0-SNAPSHOT
[INFO]   from pom.xml
[INFO] --------------------------------[ war ]---------------------------------
[INFO]
[INFO] --- resources:3.0.2:resources (default-resources) @ pro02-maven-web ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] skip non existing resourceDirectory D:\maven_workspace\spaceVideo\pro02-maven-web\src\main\resources

确实生成了一个jar包

2.6 查看依赖列表

D:\maven_workspace\spaceVideo\pro02-maven-web>mvn dependency:list
[INFO] Scanning for projects...
[INFO]
[INFO] -------------------< com.xyt.maven:pro02-maven-web >--------------------
[INFO] Building pro02-maven-web Maven Webapp 1.0-SNAPSHOT
[INFO]   from pom.xml
[INFO] --------------------------------[ war ]---------------------------------

	[INFO]
	[INFO] The following files have been resolved:
	[INFO]    junit:junit:jar:4.11:test
	[INFO]    com.xyt.maven:pro01-maven-java:jar:1.0-SNAPSHOT:compile
	[INFO]    org.hamcrest:hamcrest-core:jar:1.3:test
	[INFO]    javax.servlet:javax.servlet-api:jar:3.1.0:provided

2.7 树形结构查看

D:\maven_workspace\spaceVideo\pro02-maven-web>mvn dependency:tree
[INFO] Scanning for projects...
[INFO]
[INFO] -------------------< com.xyt.maven:pro02-maven-web >--------------------
[INFO] Building pro02-maven-web Maven Webapp 1.0-SNAPSHOT
[INFO]   from pom.xml
[INFO] --------------------------------[ war ]---------------------------------
[INFO]
[INFO] --- dependency:2.8:tree (default-cli) @ pro02-maven-web ---
[WARNING] Parameter 'localRepository' is deprecated core expression; Avoid use of ArtifactRepository type. If you need access to local repository, switch to '${repositorySystemSession}' expression and get LRM from it instead.
[INFO] com.xyt.maven:pro02-maven-web:war:1.0-SNAPSHOT
[INFO] +- junit:junit:jar:4.11:test
[INFO] |  \- org.hamcrest:hamcrest-core:jar:1.3:test
[INFO] +- javax.servlet:javax.servlet-api:jar:3.1.0:provided
[INFO] \- com.xyt.maven:pro01-maven-java:jar:1.0-SNAPSHOT:compile
[INFO] ------------------------------------------------------------------------

二 测试依赖的范围

一个depency里面有四个元素

<dependency>
<!--
通过指定被依赖工程的坐标完成依赖
-->
  <groupId>com.xyt.maven</groupId>
  <artifactId>pro01-maven-java</artifactId>
  <version>1.0-SNAPSHOT</version>
  <scope>compile</scope>
 
</dependency>

scope代表作用范围，标签的作用范围
scope提供这么多依赖的原因就是，把它测试用的test，本地提供的provided，和常规complie区分开来

compile/test/provided/system/runtime/import

开发过程有效的含义就是，在IDEA中写项目时候，我们能不能把它点出来
部署到服务器有效的含义是，把war包丢到tomcat里面时，是否包含对应文件

将这个文件里面导入

1 compile的编译过程

1.1 compile编译Calulator

在 HelloServlet 类中导入 Calculator 类，然后编译就说明有效。

D:\maven_workspace\spaceVideo\pro02-maven-web\src\main\java\xyt\maven\HelloServlet.java

引入一个测试文件

/**
* 通过import语句将要测试的类引入当前类
引入后，编译通过，可以使用，这个范围的依赖对当前类有效
引入后，编译失败，不可以使用，这个范围的依赖对当前类无效

*main目录下的java类：HelloServlet
*complie范围引入的·依赖：pro01-maven-java
*pro01-maven-java中的类：Calculator
*验证的目标：
*
*
*
*
*/
import com.xyt.maven.Calculator;
  
public class HelloServlet extends HttpServlet{
  
  protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    response.getWriter().write("hello maven web");
    
  }
  
}

D:\maven_workspace\spaceVideo\pro02-maven-web>mvn clean compile
[INFO] Scanning for projects...
[INFO]
[INFO] -------------------< com.xyt.maven:pro02-maven-web >--------------------
[INFO] Building pro02-maven-web Maven Webapp 1.0-SNAPSHOT
[INFO]   from pom.xml
[INFO] --------------------------------[ war ]---------------------------------
[INFO]
[INFO] --- clean:3.1.0:clean (default-clean) @ pro02-maven-web ---
[INFO] Deleting D:\maven_workspace\spaceVideo\pro02-maven-web\target
[INFO]
[INFO] --- resources:3.0.2:resources (default-resources) @ pro02-maven-web ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] skip non existing resourceDirectory D:\maven_workspace\spaceVideo\pro02-maven-web\src\main\resources
[INFO]
[INFO] --- compiler:3.8.0:compile (default-compile) @ pro02-maven-web ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 1 source file to D:\maven_workspace\spaceVideo\pro02-maven-web\target\classes
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS

D:\maven_workspace\spaceVideo\pro02-maven-web\pom.xml

<dependency>
<!--
通过指定被依赖工程的坐标完成依赖
-->
  <groupId>com.xyt.maven</groupId>
  <artifactId>pro01-maven-java</artifactId>
  <version>1.0-SNAPSHOT</version>
  <scope>compile</scope>
 
</dependency>

1.2 编译CalculatorTest

D:\maven_workspace\spaceVideo\pro02-maven-web>mvn clean test-compile
[INFO] Scanning for projects...
[INFO]
[INFO] -------------------< com.xyt.maven:pro02-maven-web >--------------------
[INFO] Building pro02-maven-web Maven Webapp 1.0-SNAPSHOT
[INFO]   from pom.xml
[INFO] --------------------------------[ war ]---------------------------------
[INFO]
[INFO] --- clean:3.1.0:clean (default-clean) @ pro02-maven-web ---
[INFO] Deleting D:\maven_workspace\spaceVideo\pro02-maven-web\target
[INFO]
[INFO] --- resources:3.0.2:resources (default-resources) @ pro02-maven-web ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] skip non existing resourceDirectory D:\maven_workspace\spaceVideo\pro02-maven-web\src\main\resources
[INFO]
[INFO] --- compiler:3.8.0:compile (default-compile) @ pro02-maven-web ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 1 source file to D:\maven_workspace\spaceVideo\pro02-maven-web\target\classes
[INFO]
[INFO] --- resources:3.0.2:testResources (default-testResources) @ pro02-maven-web ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] skip non existing resourceDirectory D:\maven_workspace\spaceVideo\pro02-maven-web\src\test\resources
[INFO]
[INFO] --- compiler:3.8.0:testCompile (default-testCompile) @ pro02-maven-web ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 1 source file to D:\maven_workspace\spaceVideo\pro02-maven-web\target\test-classes
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------

• 通过import语句将要测试的类引入当前类
  引入后，编译通过，可以使用，这个范围的依赖对当前类有效
  引入后，编译失败，不可以使用，这个范围的依赖对当前类无效

• main目录下的java类：HelloServlet

• complie范围引入的·依赖：pro01-maven-java

• pro01-maven-java中的类：Calculator

1.3 打包成war包

主体功能放在这个compile里面99%
打war包：

D:\maven_workspace\spaceVideo\pro02-maven-web>mvn clean compile
[INFO] Scanning for projects...
[INFO]
[INFO] -------------------< com.xyt.maven:pro02-maven-web >--------------------
[INFO] Building pro02-maven-web Maven Webapp 1.0-SNAPSHOT
[INFO]   from pom.xml
[INFO] --------------------------------[ war ]---------------------------------
[INFO]
[INFO] --- clean:3.1.0:clean (default-clean) @ pro02-maven-web ---
[INFO] Deleting D:\maven_workspace\spaceVideo\pro02-maven-web\target
[INFO]
[INFO] --- resources:3.0.2:resources (default-resources) @ pro02-maven-web ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] skip non existing resourceDirectory D:\maven_workspace\spaceVideo\pro02-maven-web\src\main\resources
[INFO]
[INFO] --- compiler:3.8.0:compile (default-compile) @ pro02-maven-web ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 1 source file to D:\maven_workspace\spaceVideo\pro02-maven-web\target\classes
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------

2 test的编译过程

2.1 main空间里面编译信息

在HttpSevelet里面导入信息

import org.junit.Test;

编译失败：验证main空间下编译这个Test依赖，会出问题

D:\maven_workspace\spaceVideo\pro02-maven-web>mvn clean compile
[INFO] Scanning for projects...
[INFO]
[INFO] -------------------< com.xyt.maven:pro02-maven-web >--------------------
[INFO] Building pro02-maven-web Maven Webapp 1.0-SNAPSHOT
[INFO]   from pom.xml
[INFO] --------------------------------[ war ]---------------------------------
[INFO]
[INFO] --- clean:3.1.0:clean (default-clean) @ pro02-maven-web ---
[INFO] Deleting D:\maven_workspace\spaceVideo\pro02-maven-web\target
[INFO]
[INFO] --- resources:3.0.2:resources (default-resources) @ pro02-maven-web ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] skip non existing resourceDirectory D:\maven_workspace\spaceVideo\pro02-maven-web\src\main\resources
[INFO]
[INFO] --- compiler:3.8.0:compile (default-compile) @ pro02-maven-web ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 1 source file to D:\maven_workspace\spaceVideo\pro02-maven-web\target\classes
[INFO] -------------------------------------------------------------
[ERROR] COMPILATION ERROR :
[INFO] -------------------------------------------------------------
[ERROR] /D:/maven_workspace/spaceVideo/pro02-maven-web/src/main/java/xyt/maven/HelloServlet.java:[25,17] 程序包org.junit不存在
[INFO] 1 error
[INFO] -------------------------------------------------------------
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  1.318 s
[INFO] Finished at: 2023-05-04T23:43:22+08:00
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.8.0:compile (default-compile) on project
 pro02-maven-web: Compilation failure
[ERROR] /D:/maven_workspace/spaceVideo/pro02-maven-web/src/main/java/xyt/maven/HelloServlet.java:[25,17] 程序包org.junit不存在

在pro01-maven-java\src\main\java\com\xyt\maven目录下修改Calculator.java

2.2 test空间下编译

<dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.11</version>
      <scope>test</scope>
    </dependency>

没问题，test必然可以在test下编译，本身test就是为test服务的
在HttpSevelet里面注释信息

//import org.junit.Test;


```bash
D:\maven_workspace\spaceVideo\pro02-maven-web>mvn clean test
[INFO] Scanning for projects...
[INFO]
[INFO] -------------------< com.xyt.maven:pro02-maven-web >--------------------
[INFO] Building pro02-maven-web Maven Webapp 1.0-SNAPSHOT
[INFO]   from pom.xml
[INFO] --------------------------------[ war ]---------------------------------
[INFO]
[INFO] --- clean:3.1.0:clean (default-clean) @ pro02-maven-web ---
[INFO] Deleting D:\maven_workspace\spaceVideo\pro02-maven-web\target
[INFO]
[INFO] --- resources:3.0.2:resources (default-resources) @ pro02-maven-web ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] skip non existing resourceDirectory D:\maven_workspace\spaceVideo\pro02-maven-web\src\main\resources
[INFO]
[INFO] --- compiler:3.8.0:compile (default-compile) @ pro02-maven-web ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 1 source file to D:\maven_workspace\spaceVideo\pro02-maven-web\target\classes
[INFO]
[INFO] --- resources:3.0.2:testResources (default-testResources) @ pro02-maven-web ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] skip non existing resourceDirectory D:\maven_workspace\spaceVideo\pro02-maven-web\src\test\resources
[INFO]
[INFO] --- compiler:3.8.0:testCompile (default-testCompile) @ pro02-maven-web ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 1 source file to D:\maven_workspace\spaceVideo\pro02-maven-web\target\test-classes
[INFO]
[INFO] --- surefire:2.22.1:test (default-test) @ pro02-maven-web ---
[WARNING] Parameter 'localRepository' is deprecated core expression; Avoid use of ArtifactRepository type. If you need access to local repository, switch to '${repositorySystemSession}' expression and get LRM from it instead.
[INFO]
[INFO] -------------------------------------------------------
[INFO]  T E S T S
[INFO] -------------------------------------------------------
[INFO] Running com.xyt.maven.CalculatorTest
输出测试的程序代码
[INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.03 s - in com.xyt.maven.CalculatorTest
[INFO]
[INFO] Results:
[INFO]
[INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0

3 provided的编译过程

3.1 test和provided不参与部署到服务器

• compile范围依赖的jar包会放入war包，通过test范围依赖的jar包不会放入war包。
• 所有东西都发给服务器，会增加服务器的负担
• 编译程序类似于火箭发射，junit类似于脚手架，不会交房交个脚手架
  
  

3.2 provided已经提供的意思

说明Tomcat里面有这个依赖，如果非要提供，会造成依赖冲突的问题
比方说jsp-api没有注明provided带进war包部署，会造成视图显示错误，造成空指针异常
NULLPOINTEREXCEPTION,

三 测试依赖的总结

1 compile:

使用第三方框架的jar包，或者项目真正需要部署的功能依赖，都用这个scope修饰
详细解释：
1)编译依赖范围（compile），该范围就是默认依赖范围，此依赖范围对 于编译、测试、运行三种classpath都有效，举个简单的例子，假如项目中有spring-core的依赖，那么spring-core不管是在编译，测试，还是运行都会被用到，因此spring-core必须是编译范围（构件默认的是编译范围，所以依赖范围是编译范围的无须显示指定）

<dependency>
 <groupId>org.springframework</groupId>
 <artifactId>spring-core</artifactId>
 <version>2.5</version>
 <scope>compile</scope> <!--默认为该依赖范围，无须显示指定--〉
</dependency>

2 test

测试过程中使用的jar包，以test范围写进来，比如junit
详细解释

顾名思义就是针对于测试的，使用此依赖范围的依赖，只对测试classpath有效，在编译主代码和项目运行时，都将无法使用该依赖，最典型的例子就是 Junit, 构件在测试时才需要，所以它的依赖范围是测试，因此它的依赖范围需要显示指定为test ,当然不显示指定依赖范围也不会报错，但是该依赖会被加入到编译和运行的classpath中,造成不必要的浪费 。

 <dependency>
     <groupId>junit</groupId>
     <artifactId>junit</artifactId>
     <version>4.7</version>
    <scope>test</scope>
    </dependency>

3 provided

主要是为了减轻服务器的负担，避免依赖冲突，比方说本地项目中有jsp-api.jar,但是tomcat里面也有这个文件，如果硬要导入，就会产生冲突，报空指针异常

典型的例子就是servlet-api， 编译和测试该项目的时候需要该依赖，但是在运行时，web容器已经提供的该依赖，所以运行时就不再需要此依赖，如果不显示指定该依赖范围，并且容器依赖的版本和maven依赖的版本不一致的话，可能会引起版本冲突，造成不良影响。文章来源地址https://www.toymoban.com/news/detail-434316.html

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