springboot中mybatis逆向工程与分页的应用

最近在项目中应用到springboot与mybatis，在进行整合过程中遇到一些坑，在此将其整理出来，便于以后查阅与复习。
项目运行环境为：eclispe+jdk1.8+maven

一、搭建Spring Boot环境

首先建立maven project,在生成的pom文件中加入依赖，代码如下：

<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>1.5.2.RELEASE</version>
    <relativePath/> <!-- lookup parent from repository -->
</parent>

<properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
    <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-test</artifactId>
    </dependency>
    
    <dependency>
        <groupId>org.mybatis.spring.boot</groupId>
        <artifactId>mybatis-spring-boot-starter</artifactId>
        <version>1.3.0</version>
    </dependency>
    
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <scope>runtime</scope>
    </dependency>
    
    <!--分页插件-->
	<dependency>
	      <groupId>com.github.pagehelper</groupId>
	      <artifactId>pagehelper-spring-boot-starter</artifactId>
	      <version>1.2.1</version>
	</dependency>
    
    <!-- alibaba的druid数据库连接池 -->
    <dependency>
    	<groupId>com.alibaba</groupId>
    	<artifactId>druid</artifactId>
    	<version>1.0.29</version>
    </dependency>
</dependencies>

<build>
    <plugins>
        <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
        </plugin>
        <!-- mybatis generator 自动生成代码插件 -->
        <plugin>
            <groupId>org.mybatis.generator</groupId>
            <artifactId>mybatis-generator-maven-plugin</artifactId>
            <version>1.3.2</version>
            <configuration>
                <configurationFile>${basedir}/src/main/resources/generator/generatorConfig.xml</configurationFile>
                <overwrite>true</overwrite>
                <verbose>true</verbose>
            </configuration>
        </plugin>
    </plugins>
</build>

配置好依赖后进行maven install,此时注意的坑：
坑一：启动maven install报错：

[ERROR] Failed to execute goal org.springframework.boot:spring-boot-maven-plugin:1.5.2.RELEASE:repackage (default) on project springboot-mybatis: Execution default of goal org.springframework.boot:spring-boot-maven-plugin:1.5.2.RELEASE:repackage failed: Unable to find main class -> [Help 1]
[ERROR] 
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR] 
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/PluginExecutionException

报错原因是没有启动类
解决方法:编写启动类Main.java正常运行！

@SpringBootApplication
public class Main {
	public static void main(String[] args) {
		SpringApplication.run(Main.class, args);
	}
}

坑二：启动maven install报错：

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.1:compile (default-compile) on project springboot-mybatis: Compilation failure
[ERROR] No compiler is provided in this environment. Perhaps you are running on a JRE rather than a JDK?
[ERROR] -> [Help 1]
[ERROR] 
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR] 
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoFailureException

报错原因：项目的java环境与电脑环境不符合，例如我的新建项目运行环境为J2SE-1.5,报错是在我将其改为jre1.8之后
解决方案：
右键项目——build path——Configure build path——Libraries——双击Jre System Libraries如下图所示：

选择Alternate JRE 如2处的下拉框只有jre，点击3处的Install JREs，依次经过add——Standard VM——next——Directory,选择本机的jdk位置点击finish
在install JREs位置将默认勾选更改jdk,如下图所示，并保存。

再次maven install项目正常。如下所示：

[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 3.351 s
[INFO] Finished at: 2018-09-05T21:20:48+08:00
[INFO] Final Memory: 23M/181M
[INFO] ------------------------------------------------------------------------

在src/main/resources新建文件：application.yml，内容如下所示：

server:
  port: 8080

spring:
	datasource:
		name: test
		url: jdbc:mysql://localhost:3306/test
		username: root
		password: 123456
		driver-class-name: com.mysql.jdbc.Driver

## 该配置节点为独立的节点
mybatis:
  mapper-locations: classpath:mapper/*.xml
  
#pagehelper分页插件
pagehelper:
	helperDialect: mysql
	reasonable: true
	supportMethodsArguments: true
	params: count=countSql

至此springboot环境搭建完毕！

二、逆向工程应用

首先应该注意到在pom文件中有配置逆向工程xml文件的位置：src/main/resources/generator/generatorConfig.xml
因而在src/main/resources下新建generator文件夹，并建立generatorConfig.xml文件，代码如下：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE generatorConfiguration PUBLIC "-//mybatis.org//DTD MyBatis Generator Configuration 1.0//EN" "http://mybatis.org/dtd/mybatis-generator-config_1_0.dtd">
<generatorConfiguration>
	<!-- 数据库驱动:选择你的本地硬盘上面的数据库驱动包-->
	<classPathEntry  location="E:\plugins\maven\repo\mysql\mysql-connector-java\5.1.41\mysql-connector-java-5.1.41.jar"/>
	<context id="DB2Tables"  targetRuntime="MyBatis3">
		<commentGenerator>
			<property name="suppressDate" value="true"/>
			<!-- 是否去除自动生成的注释 true：是 ： false:否 -->
			<property name="suppressAllComments" value="true"/>
		</commentGenerator>
		<!--数据库链接URL，用户名、密码 -->
		<jdbcConnection driverClass="com.mysql.jdbc.Driver" connectionURL="jdbc:mysql://localhost/test" userId="root" password="123456">
		</jdbcConnection>
		<javaTypeResolver>
			<property name="forceBigDecimals" value="false"/>
		</javaTypeResolver>
		<!-- 生成pojo类的位置-->
		<javaModelGenerator targetPackage="com.luis.entity" targetProject="src/main/java">
			<property name="enableSubPackages" value="true"/>
			<property name="trimStrings" value="true"/>
		</javaModelGenerator>
		<!-- 生成映射文件的包名和位置-->
		<sqlMapGenerator targetPackage="mapper" targetProject="src/main/resources">
			<!-- enableSubPackages 是否让schema作为包的后缀-->
			<property name="enableSubPackages" value="false"/>
		</sqlMapGenerator>
		<!-- 生成mapper接口的位置-->
		<javaClientGenerator type="XMLMAPPER" targetPackage="com.luis.mapper" targetProject="src/main/java">
			<!-- enableSubPackages 是否让schema作为包的后缀-->
			<property name="enableSubPackages" value="false"/>
		</javaClientGenerator>
		<!-- 指定数据库表 -->
		<table schema="" tableName="user"></table>
	</context>
</generatorConfiguration>

根据个人环境将配置文件中的配置进行更改，如数据库密码，包名，对应数据库表
所用的数据库表如下：

DROP TABLE IF EXISTS `user`;
CREATE TABLE `user` (
  `id` bigint(20) NOT NULL,
  `name` varchar(255) NOT NULL,
  `age` int(4) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

INSERT INTO `user` VALUES ('1', 'wanger', '22');
INSERT INTO `user` VALUES ('2', 'zhangsan', '18');
INSERT INTO `user` VALUES ('3', 'lisi', '23');
INSERT INTO `user` VALUES ('4', 'wangwu', '21');

配置完成后，右键项目，选择run as——Maven build——在下面两处分别填入：
Goals: mybatis-generator:generate -e
Profiles: generatorConfig.xml
如下图所示：

出现如下所示，代码生成成功，刷新项目即可。

[INFO] Generating Example class for table user
[INFO] Generating Record class for table user
[INFO] Generating Mapper Interface for table user
[INFO] Generating SQL Map for table user
[INFO] Saving file UserMapper.xml
[INFO] Saving file UserExample.java
[INFO] Saving file User.java
[INFO] Saving file UserMapper.java
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------

需要注意的是：逆向工程生成的代码不会覆盖，因而不能重复多次生成。
此处也有个小坑，逆向工程的代码生成后，启动项目会报如下错误：

***************************
APPLICATION FAILED TO START
***************************

Description:

Field userMapper in com.luis.service.impl.UserServiceImpl required a bean of type 'com.luis.mapper.UserMapper' that could not be found.


Action:

Consider defining a bean of type 'com.luis.mapper.UserMapper' in your configuration.

解决方案：
1、给生成的mapper接口文件前加注解：@Mapper 即可解决。但需要给每一个mapper文件前加，繁琐，因而有第二种类解决办法
2、在启动类前加@MapperScan({"com.luis.mapper"})，其中com.luis.mapper为mapper文件的所在位置。
参考自：http://412887952-qq-com.iteye.com/blog/2392672

三、分页应用

逆向工程已经生成了entity类，及dao层的mapper接口与*mapper.xml文件，因而/只用编写service层与web层。
首先在UserService中编写接口，代码如下：

public interface UserService {
	User selectByName(String name);
	List<User> findAllUser(int pageNum, int pageSize);
}

在UserServiceImpl文件进行实现，代码如下所示：

@Service
public class UserServiceImpl implements UserService {

	@Autowired
	private UserMapper userMapper;
	
	@Override
	public User selectByName(String name) {
		UserExample example = new UserExample();
		Criteria criteria = example.createCriteria();
		criteria.andNameEqualTo(name);
		List<User> users = userMapper.selectByExample(example);
		if (users != null && users.size() > 0) {
			return users.get(0);
		}
		return null;
	}
	
	/**
	 * pageNum 开始页数
	 * pageSize 每页显示的数据条数
	 */
	@Override
	public List<User> findAllUser(int pageNum, int pageSize) {
		//将参数传给方法实现分页
		PageHelper.startPage(pageNum, pageSize);
		UserExample example = new UserExample();
		List<User> list = userMapper.selectByExample(example);
		return list;
	}
}

最后在controller层对查询结果进行接收，UserController代码如下：

@Controller
@RestController
public class UserController {
	
	@Autowired
	private UserService userService;
	
	@RequestMapping("/test")
	public User querUserByName() {
		User user = userService.selectByName("luis");
		System.out.println(user.toString());
		return user;
	}
	
	@RequestMapping("/list")
	public List<User> querUser() {
		List<User> list = userService.findAllUser(1, 2);
		//获取分页信息
		PageInfo<User> pageInfo = new PageInfo<>(list);
		System.out.println("total:" + pageInfo.getTotal());
		System.out.println("pages:" + pageInfo.getPages());
		System.out.println("pageSize:" + pageInfo.getPageSize());
		return list;
	}
}

四、测试

此前在项目编写过程中已经对可能出现的错误进行了总结，最后，对项目的功能进行测试，通过加@RestController注解将数据传输到浏览器中。
测试mybatis与springboot，浏览器输入http://localhost:8080/test，浏览器输出：

{"id":1,"name":"wanger","age":22}

分页测试，浏览器输入http://localhost:8080/list，浏览器输出：

[{"id":1,"name":"wanger","age":22},{"id":2,"name":"zhangsan","age":18}]

eclipse输出：

total:4
pages:2
pageSize:2

项目搭建完毕，具体代码参见github

本文参考了：
http://412887952-qq-com.iteye.com/blog/2392672
https://blog.csdn.net/rico_rico/article/details/79408474
https://blog.csdn.net/winter_chen001/article/details/77249029