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，现记录如下。为展示所遇问题，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创建代码，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

创建库ssm和表users，其中创建表users的SQL如下。

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=latin1insert 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，其源码如下。

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文件如下。

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE generatorConfigurationPUBLIC "-//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。 子元素用于指定要连接到的数据库、 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><!--数据库连接的信息：驱动类、连接地址、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项目需要指定绝对路径--><javaModelGenerator targetPackage="com.leesf.po"targetProject="F:/01_Code/01_Idea/ssm-master/src/main/java"><!-- enableSubPackages:是否让schema作为包的后缀 --><property name="enableSubPackages" value="false"/><!-- 从数据库返回的值被清理前后的空格 --><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作为包的后缀 --><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作为包的后缀 --><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> --><!-- 有些表的字段需要指定java类型<table schema="" tableName=""><columnOverride column="" javaType="" /></table> --></context>
</generatorConfiguration>

WebServer

WebServer为Web容器，其源码如下。

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，只做演示，其中参数并未进行调优处理。

Controller

只存在UserController，其源码如下。

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);}
}

可以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

其源码如下。

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;}
}

可以看到，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，发现构造了如下SQL语句，

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

url访问结果如下：

{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

其源码如下

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可以匹配address或者hobby，而name必须要匹配name，也就是希望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。

结果如下

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

可以看到访问结果中result_content为空，查看运行日志，发现如下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并非之前所想的那样，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，需要进行等价变化，即(a or b) and c = (a and c) or (b and c)，具体可查看如下链接，按照这样的思路进行如下修改。

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，发现还是没有结果，查看运行时信息发现如下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，但是就是出不来结果，like和前面也是一样的，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，修改如下。

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;}

重新运行并访问url，得到如下结果：

{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使用的情况下，like必须显示添加%才能生效，虽然按照这种等价的方式可以进行处理，还是有些麻烦，特别是当or字段非常多的时候，处理比较麻烦，如(a or b or c or d) and e，其需要处理成(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，进行如下改造。

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如下。

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，结果如下。

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

总结

可以看到使用MyBatisGenerator自动生成代码时，需要注意如下可能出现的坑。

• 当进行(a or b) and c查询时，可通过转变为(a and c) or (b and c)方式进行查询，但个人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，不需要添加"%"处理，而配合or时，必须添加"%"才行。