【MyBatis】MyBatis自动生成代码之查询爬坑记

前言

项目使用SSM框架搭建Web后台服务，前台后使用restful api，后台使用MyBatisGenerator自动生成代码，在前台使用关键字进行查询时，遇到了一些很宝贵的坑，现记录以下。为展现所遇问题，将项目进行了精简。

项目框架

后台框架

后台框架选型为Spring + SpringMVC + Mybatis + Jetty，其中使用MyBatisGenerator建立代码，Jetty为内嵌的Web服务器。

项目代码

代码已上传至github

项目介绍

数据准备

建立库ssm和表users，其中建立表users的SQL以下。

CREATE TABLE `users` (
  `id` int(10) NOT NULL AUTO_INCREMENT,
  `name` varchar(32) DEFAULT NULL,
  `address` varchar(32) DEFAULT NULL,
  `hobby` varchar(64) DEFAULT NULL,
  `content` text,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1

insert into users(name, address, hobby, content) values("leesf", "hubei", "sport, race", "he is a boy");
insert into users(name, address, hobby, content) values("dyd", "hubei", "painting, reading", "she is a girl");

自动生成代码框架

使用MyBatisGenerator自动生成相应代码，其源码以下。

package com.leesf;

import org.junit.Test;
import org.mybatis.generator.api.MyBatisGenerator;
import org.mybatis.generator.config.Configuration;
import org.mybatis.generator.config.xml.ConfigurationParser;
import org.mybatis.generator.internal.DefaultShellCallback;

import java.io.File;
import java.util.ArrayList;
import java.util.List;

public class MybatisGenerator {
  @Test public void generator() throws Exception {
    List<String> warnings = new ArrayList<String>();
    File configFile = new File(
        "F:/01_Code/01_Idea/ssm-master/src/test/generatorConfig.xml");
    ConfigurationParser cp = new ConfigurationParser(warnings);
    Configuration config = cp.parseConfiguration(configFile);
    DefaultShellCallback callback = new DefaultShellCallback(true);
    MyBatisGenerator myBatisGenerator =
        new MyBatisGenerator(config, callback, warnings);
    myBatisGenerator.generate(null);
  }
}

其中generatorConfig.xml文件以下。

<?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>
    <!-- <context> 元素用于指定生成一组对象的环境。 子元素用于指定要链接到的数据库、 要生成对象的类型和要内省的表 -->
    <context id="testTables" targetRuntime="MyBatis3">
        <commentGenerator>
            <!-- 是否去除自动生成的注释 true：是 ： false:否 -->
            <property name="suppressAllComments" value="true"/>
        </commentGenerator>
        <!--数据库链接的信息：驱动类、链接地址、用户名、密码 -->
        <jdbcConnection driverClass="com.mysql.jdbc.Driver"
                        connectionURL="jdbc:mysql://localhost:3306/ssm?useUnicode=true&amp;characterEncoding=UTF-8"
                        userId="root"
                        password="">
        </jdbcConnection>

        <!-- 默认false，把JDBC DECIMAL 和 NUMERIC 类型解析为 Integer，为 true时把JDBC DECIMAL 和
            NUMERIC 类型解析为java.math.BigDecimal -->
        <javaTypeResolver>
            <property name="forceBigDecimals" value="false"/>
        </javaTypeResolver>

        <!-- targetProject:生成PO类的位置
         注意对于targetProject：In other environments（other than Eclipse）,
         this value should be an existing directory on the local file system.
         即对于非eclipse项目须要指定绝对路径
         -->
        <javaModelGenerator targetPackage="com.leesf.po"
                            targetProject="F:/01_Code/01_Idea/ssm-master/src/main/java">
            <!-- enableSubPackages:是否让schema做为包的后缀 -->
            <property name="enableSubPackages" value="false"/>
            <!-- 从数据库返回的值被清理先后的空格 -->
            <property name="trimStrings" value="true"/>
        </javaModelGenerator>

        <!-- targetProject:mapper映射文件生成的位置 -->
        <sqlMapGenerator targetPackage="com.leesf.mapper"
                         targetProject="F:/01_Code/01_Idea/ssm-master/src/main/java">
            <!-- enableSubPackages:是否让schema做为包的后缀 -->
            <property name="enableSubPackages" value="false"/>
        </sqlMapGenerator>

        <!-- targetPackage：mapper接口生成的位置 -->
        <javaClientGenerator type="XMLMAPPER"
                             targetPackage="com.leesf.mapper"
                             targetProject="F:/01_Code/01_Idea/ssm-master/src/main/java">
            <!-- enableSubPackages:是否让schema做为包的后缀 -->
            <property name="enableSubPackages" value="false"/>
        </javaClientGenerator>

        <!-- 指定数据库表 -->
        <table tableName="users"></table>

        <!-- <table schema="" tableName="sys_user"></table>
        <table schema="" tableName="sys_role"></table>
        <table schema="" tableName="sys_permission"></table>
        <table schema="" tableName="sys_user_role"></table>
        <table schema="" tableName="sys_role_permission"></table> -->

        <!-- 有些表的字段须要指定java类型
         <table schema="" tableName="">
            <columnOverride column="" javaType="" />
        </table> -->
    </context>
</generatorConfiguration>

WebServer

WebServer为Web容器，其源码以下。

package com.leesf.main;

import java.net.UnknownHostException;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.TimeUnit;

import org.apache.commons.lang3.StringUtils;
import org.eclipse.jetty.server.Connector;
import org.eclipse.jetty.server.Server;
import org.eclipse.jetty.server.nio.SelectChannelConnector;
import org.eclipse.jetty.util.thread.ExecutorThreadPool;
import org.eclipse.jetty.webapp.WebAppContext;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class WebServer {
  public static final String CONTEXT = "/";
  private static final Logger LOG = LoggerFactory.getLogger(WebServer.class);
  private static final String DEFAULT_WEBAPP_PATH = "webapps/";
  private Server server;
  private int port;

  public WebServer() {
  }

  public Server createServerInSource() throws UnknownHostException {
    port = 8081;
    server = new Server();
    server.setStopAtShutdown(true);
    SelectChannelConnector connector = new SelectChannelConnector();
    connector.setPort(port);
    connector.setReuseAddress(false);

    connector.setAcceptQueueSize(50);
    connector.setAcceptors(2);
    connector.setThreadPool(
        new ExecutorThreadPool(20,
            40, 0, TimeUnit.SECONDS,
            new ArrayBlockingQueue<Runnable>(
                16, false)));
    connector.setLowResourcesMaxIdleTime(3000);

    connector.setReuseAddress(true);
    connector.setRequestBufferSize(
        16 * 1024);
    connector.setRequestHeaderSize(
        8 * 1024);

    server.setConnectors(new Connector[] { connector });

    String basePath = "src/main/webapps";
    if (StringUtils.isEmpty(basePath)) {
      basePath = DEFAULT_WEBAPP_PATH;
    }
    WebAppContext webContext = new WebAppContext(basePath, CONTEXT);
    webContext.setContextPath(CONTEXT);
    webContext.setDescriptor(basePath + "/WEB-INF/web.xml");
    System.out.println("-------------web.xml path is " + webContext.getDescriptor()
        + "--------------");
    webContext.setResourceBase(basePath);
    webContext.setClassLoader(Thread.currentThread().getContextClassLoader());
    server.setHandler(webContext);
    return server;
  }

  public void start() throws Exception {
    if (server == null) {
      createServerInSource();
    }
    if (server != null) {
      server.start();
      LOG.info("WebServer has started at port:" + port);
    }
  }

  public void stop() throws Exception {
    if (server != null) {
      server.stop();
    }
  }

  public static void main(String[] args) throws Exception {
    WebServer webServer = new WebServer();
    webServer.start();
  }
}

使用内嵌Jetty方式提供Web服务，只作演示，其中参数并未进行调优处理。

Controller

只存在UserController，其源码以下。

package com.leesf.controller;

import com.leesf.po.Users;
import com.leesf.service.UserService;
import com.leesf.utils.ResultUtils;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.ResponseBody;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.OutputStreamWriter;
import java.util.List;

@Controller @RequestMapping(value = "/users")
public class UserController {
  @Autowired UserService userService;

  @ResponseBody @RequestMapping(value = "/listUsers", method = {
      RequestMethod.POST, RequestMethod.GET }) public void listUsers(
      HttpServletRequest request, HttpServletResponse response,
      @RequestParam(required = false) String name,
      @RequestParam(required = false) String key) throws Exception {
    System.out.println("xxxxxx");
    OutputStreamWriter out = new OutputStreamWriter(response.getOutputStream());
    List<Users> users = userService.getUsers(name, key);
    ResultUtils.resultSuccess(users, out);
  }
}

能够根据用户名字和关键字查询用户。

Service

UserServiceImp为UserService的实现类。

1. 根据用户名查询指定记录

其源码以下。

package com.leesf.service.impl;

import com.leesf.mapper.UsersMapper;
import com.leesf.po.Users;
import com.leesf.po.UsersExample;
import com.leesf.service.UserService;
import org.apache.commons.lang3.StringUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.HashMap;
import java.util.List;
import java.util.Map;

@Service("userService") public class UserServiceImp implements UserService {
  @Autowired UsersMapper usersMapper;
  private Logger LOG = LoggerFactory.getLogger(this.getClass());

  public List<Users> getUsers(String name, String key) {
    UsersExample usersExample = new UsersExample();

    usersExample.createCriteria().andNameLike(name);

    List<Users> users = usersMapper.selectByExampleWithBLOBs(usersExample);
    return users;
  }
}

能够看到，该Service根据name查找匹配name的记录，启动WebServer，访问http://localhost:8081/users/listUsers?name=sport，查看编译器运行的信息，发现构造了以下SQL语句，

select id, name, address, hobby , content from users WHERE ( name like ? )。

url访问结果以下：

{
    result_code: "0",
    result_msg: "Succeed!",
    result_content: [{
        id: 1,
        name: "leesf",
        address: "hubei",
        hobby: "sport, race",
        content: "he is a boy"
    }]
}

1. 根据用户名和关键字查询指定记录

其源码以下

package com.leesf.service.impl;

import com.leesf.mapper.UsersMapper;
import com.leesf.po.Users;
import com.leesf.po.UsersExample;
import com.leesf.service.UserService;
import org.apache.commons.lang3.StringUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.HashMap;
import java.util.List;
import java.util.Map;

@Service("userService") public class UserServiceImp implements UserService {
  @Autowired UsersMapper usersMapper;
  private Logger LOG = LoggerFactory.getLogger(this.getClass());

  public List<Users> getUsers(String name, String key) {
    UsersExample usersExample = new UsersExample();

    if (StringUtils.isNotEmpty(key)) {
      usersExample.or().andAddressLike(key);
      usersExample.or().andHobbyLike(key);
    }

    if (StringUtils.isNotEmpty(name)) {
      if (usersExample.getOredCriteria().size() == 0){
        usersExample.createCriteria();
      }
      usersExample.getOredCriteria().get(0).andNameEqualTo(name);
    }

    List<Users> users = usersMapper.selectByExampleWithBLOBs(usersExample);
    return users;
  }
}

key能够匹配address或者hobby，而name必需要匹配name，也就是但愿构造这样的一条查询SQLselect * from users where (address like "%sport%" or hobby like "%sport%") and name = "leesf"。

启动WebServer，访问http://localhost:8081/users/listUsers?key=sport&name=leesf。

结果以下

{
    result_code: "0",
    result_msg: "Succeed!",
    result_content: []
}

能够看到访问结果中result_content为空，查看运行日志，发现以下SQL语句

select id, name, address, hobby , content from users WHERE ( address like ? and name = ? ) or( hobby like ? )

程序实际构造的SQL并不是以前所想的那样，此时查阅资料，发现MyBatis自动生成代码还不支持纯生的(a or b) and c 这样的SQL语句，须要进行等价变化，即(a or b) and c = (a and c) or (b and c)，具体可查看以下连接，按照这样的思路进行以下修改。

public List<Users> getUsers(String name, String key) {
    UsersExample usersExample = new UsersExample();

    if (StringUtils.isNotEmpty(key)) {
      usersExample.or().andAddressLike(key);
      usersExample.or().andHobbyLike(key);
    }

    if (StringUtils.isNotEmpty(name)){
      if (usersExample.getOredCriteria().size() == 0){
        usersExample.createCriteria();
      }
      usersExample.getOredCriteria().get(0).andNameEqualTo(name);
      usersExample.getOredCriteria().get(1).andNameEqualTo(name);
    }

    List<Users> users = usersMapper.selectByExampleWithBLOBs(usersExample);
    return users;
  }

此时，再次查询，发现仍是没有结果，查看运行时信息发现以下SQL。

select id, name, address, hobby , content from users WHERE ( address like ? and name = ? ) or( hobby like ? and name = ? )，看似SQL语句没有任何问题，可是就是出不来结果，like和前面也是同样的，百思不得其解，继续查阅资料也无解，后面尝试对like添加%处理，修改以下。

public List<Users> getUsers(String name, String key) {
    UsersExample usersExample = new UsersExample();

    if (StringUtils.isNotEmpty(key)) {
      usersExample.or().andAddressLike("%" + key + "%");
      usersExample.or().andHobbyLike("%" + key + "%");
    }

    if (StringUtils.isNotEmpty(name)) {
      if (usersExample.getOredCriteria().size() == 0){
        usersExample.createCriteria();
      }
      usersExample.getOredCriteria().get(0).andNameEqualTo(name);
      usersExample.getOredCriteria().get(1).andNameEqualTo(name);
    }

    List<Users> users = usersMapper.selectByExampleWithBLOBs(usersExample);
    return users;
  }

从新运行并访问url，获得以下结果：

{
    result_code: "0",
    result_msg: "Succeed!",
    result_content: [{
        id: 1,
        name: "leesf",
        address: "hubei",
        hobby: "sport, race",
        content: "he is a boy"
    }]
}

在配合or使用的状况下，like必须显示添加%才能生效，虽然按照这种等价的方式能够进行处理，仍是有些麻烦，特别是当or字段很是多的时候，处理比较麻烦，如(a or b or c or d) and e，其须要处理成(a and e) or (b and e) or (c and e) or (d and e)，继续查阅资料，看是否有更为简便的写法，在stackoverflow上发现有这样的处理方式，进行以下改造。

public List<Users> getUsers(String name, String key) {
    UsersExample usersExample = new UsersExample();

    if (StringUtils.isNotEmpty(key)) {
      Map<String, String> maps = new HashMap<String, String>();
      maps.put("address", key);
      maps.put("hobby", key);
      usersExample.createCriteria().multiColumnOrLike(maps);
    }

    if (StringUtils.isNotEmpty(name)) {
      if (usersExample.getOredCriteria().size() == 0){
        usersExample.createCriteria();
      }
      usersExample.getOredCriteria().get(0).andNameEqualTo(name);
    }

    List<Users> users = usersMapper.selectByExampleWithBLOBs(usersExample);
    return users;
  }

修改UserExample.java的Criteria以下。

public static class Criteria extends GeneratedCriteria {

        protected Criteria() {
            super();
        }

        public Criteria multiColumnOrLike(Map<String, String> maps) {
            StringBuffer stringBuffer = new StringBuffer();
            stringBuffer.append("( ");
            for (Map.Entry<String, String> entry : maps.entrySet()) {
                stringBuffer.append(entry.getKey());
                stringBuffer.append(" like ");
                stringBuffer.append("\"%");
                stringBuffer.append(entry.getValue());
                stringBuffer.append("%\"");
                stringBuffer.append(" or ");
            }

            int index = stringBuffer.lastIndexOf("or");
            stringBuffer.delete(index, stringBuffer.length());
            stringBuffer.append(")");
            addCriterion(stringBuffer.toString());
            return this;
        }
    }

再次启动运行，结果以下。

{
    result_code: "0",
    result_msg: "Succeed!",
    result_content: [{
        id: 1,
        name: "leesf",
        address: "hubei",
        hobby: "sport, race",
        content: "he is a boy"
    }]
}

总结

能够看到使用MyBatisGenerator自动生成代码时，须要注意以下可能出现的坑。

• 当进行(a or b) and c查询时，可经过转变为(a and c) or (b and c)方式进行查询，但我的认为更好的方法是修改Example文件，进行定制化的查询处理。
• 单独使用andxxxLike时，不须要添加"%"处理，而配合or时，必须添加"%"才行。