maven作用原理及父子級繼承使用

maven主要作用：在需要高並發訪問條件下構建分區集群項目時，提供一個穩定版本依賴和排除重復jar包引入，減少結構冗余，從側面增加代碼運行速度

首先，我們要測試父子級繼承依賴，就需要准備項目，目錄如下：

首先在父工程（test）的pom.xml文件中引入經過dependencyManagement束縛的jar包，以便子工程進行重寫引用

<?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.aaa.fx.maven</groupId>
    <artifactId>test</artifactId>
    <packaging>pom</packaging>
    <version>1.0-SNAPSHOT</version>
    <!--//此處為已經被引用的module文件：-->
    <modules>
        <module>mapper</module>
        <module>model</module>
        <module>service</module>
        <module>web</module>
    </modules>

    <!--dependencyManagement此標簽為設定jar包不會對子對象繼承，子對象若需要繼承則需要在自己的pom.xml文件中進行特殊聲明重寫，需要注意的是。重寫的時候不需要加版本號-->
    <dependencyManagement>
        <dependencies>
            <!--
                此為mysql的驅動包
            -->
            <dependency>
                <groupId>mysql</groupId>
                <artifactId>mysql-connector-java</artifactId>
                <version>5.1.38</version>
            </dependency>
            <dependency>
                <groupId>net.sourceforge.nekohtml</groupId>
                <artifactId>nekohtml</artifactId>
                <version>1.9.21</version>
            </dependency>
            <!--
                spring
            -->
            <!--
                mybatis
            -->
            <!--
                shiro
            -->
        </dependencies>
    </dependencyManagement>
</project>

接着在model中書寫實體類：

package com.aaa.fx.maven.model;

import java.io.Serializable;
import java.util.Objects;

/**
 * 首先，實體類需要實現序列化接口
 * 定義對象屬性全部使用引用類型，防止空指針異常（引用類型為空則為null）
 * 實現getset方法
 * 重寫equals和hashCode方法
 */
public class User implements Serializable {
    private Long id;
    private String username;
    private String password;
    private Integer age;


    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        User user = (User) o;
        return Objects.equals(id, user.id) &&
                Objects.equals(username, user.username) &&
                Objects.equals(password, user.password) &&
                Objects.equals(age, user.age);
    }


    @Override
    public int hashCode() {
        return Objects.hash(id, username, password, age);
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", password='" + password + '\'' +
                ", age=" + age +
                '}';
    }
}

由於實體類無需特殊引用  所以接下來直接進到mapper目錄下書寫mapper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">
    <parent>
        <artifactId>test</artifactId>
        <groupId>com.aaa.fx.maven</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>mapper</artifactId>

    <dependencies>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <!--無需書寫版本號，因為此為繼承/重寫敷方法中的dependencyManagement中的jar包-->
            <!--若強行書寫，則會到倉庫中下載，造成jar包導入重復和冗余-->
        </dependency>
        <!--需要用到實體類，則在此處引入model實體類,便可以在mapper的Module下使用model中的實體類，此為跨域引用-->
        <dependency>
            <groupId>com.aaa.fx.maven</groupId>
            <artifactId>model</artifactId>
            <version>1.0-SNAPSHOT</version>
        </dependency>
    </dependencies>
</project>

接下來我肯可以看到  已經可以成功使用我們在model中定義好的User對象了

package com.aaa.fx.maven.mapper;

import com.aaa.fx.maven.model.User;

import java.util.List;

public interface UserMapper {

    List<User> selectAll();
}

進入service中配置servie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">
    <parent>
        <artifactId>test</artifactId>
        <groupId>com.aaa.fx.maven</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>service</artifactId>

    <!--service需要用到mapper，故在此處引入mapper，進行跨域-->
    <dependencies>
        <dependency>
            <groupId>com.aaa.fx.maven</groupId>
            <artifactId>mapper</artifactId>
            <version>1.0-SNAPSHOT</version>
        </dependency>
    </dependencies>


</project>

書寫我們的service:

package com.aaa.fx.maven.service;

import com.aaa.fx.maven.mapper.UserMapper;
import com.aaa.fx.maven.model.User;

import java.util.ArrayList;
import java.util.List;

public class UserService {
    UserMapper userMapper = new UserMapper() {
        public List<User> selectAll() {
//            搞一個User對象放入List<User>的集合當中映射數據庫返回值對象
            User user = new User();
            //1L的L有必要大寫，和小寫的I和1用以區分
            user.setId(1L);
            user.setAge(15);
            user.setUsername("admin");
            user.setPassword("Moon-history");
//            這不，搞出來一個List<User>類型的arraylist對象，然后將設置好值的user放進去
            List<User> userList = new ArrayList<User>();
            userList.add(user);
            return userList;
        }
    };
}

可以看到我們成功引用了mapper

最后的web中的pom.xml:

<?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">
    <parent>
        <artifactId>test</artifactId>
        <groupId>com.aaa.fx.maven</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>web</artifactId>

    <!--當然，最后需要在頁面顯示測試了，那么引入service文件-->
    <dependencies>
        <dependency>
            <groupId>com.aaa.fx.maven</groupId>
            <artifactId>service</artifactId>
            <version>1.0-SNAPSHOT</version>
        </dependency>
    </dependencies>

</project>

接着是最后的web中的controller:

package com.aaa.fx.maven.web;

import com.aaa.fx.maven.service.UserService;

public class UserController {
    UserService userService = new UserService();
    //成功搞到，那么結束！
}

The end~~~~~~