spring+mybatis的插件【shardbatis2.0】+mysql+java自定义注解实现分表

一、业务场景分析

只有大表才需要分表，而且这个大表还会有经常需要读的需要，即使经过sql服务器优化和sql调优，查询也会非常慢。例如共享汽车的定位数据表等。

二、实现步骤

1.准备pom依赖

<dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.30</version>
    </dependency>
    <dependency>
        <groupId>com.alibaba</groupId>
        <artifactId>druid</artifactId>
        <version>1.1.3</version>
    </dependency>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-jdbc</artifactId>
        <version>4.3.11.RELEASE</version>
    </dependency>

    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis-spring</artifactId>
        <version>1.2.1</version>
    </dependency>
    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.2.3</version>
    </dependency>

这里关键是要额外引入 插件shardbatis 相关的依赖，主要有两个：

<dependency>
        <groupId>org.shardbatis</groupId>
        <artifactId>shardbatis</artifactId>
        <version>2.0.0B</version>
    </dependency>
    <dependency>
        <groupId>net.sf.jsqlparser</groupId>
        <artifactId>jsqlparser</artifactId>
        <version>0.7.0</version>
    </dependency>

2.准备表

把原来的t_location单表拆分成t_location_01、t_location_02、t_location_03、t_location_04、t_location_05、t_location_06

3.准备好mybatis的mapper interface

public interface UserMapper {
        int deleteByPrimaryKey(Integer id);
        int insert(User record);
        int insertSelective(User record);
        User selectByPrimaryKey(Integer id);
        int updateByPrimaryKeySelective(User record);
        int updateByPrimaryKey(User record);
    }

对应的sql这里就省略了，shardbatis这个插件使用时也不需要去调整实际的sql，插件达到的效果就是替换掉实际sql中的表名。

4.新增一个shard_config.xml文件

<?xml version="1.0" encoding="UTF-8"?>
    <!DOCTYPE shardingConfig PUBLIC "-//shardbatis.googlecode.com//DTD Shardbatis 2.0//EN"
            "http://shardbatis.googlecode.com/dtd/shardbatis-config.dtd">
    <shardingConfig>
        <!--
            parseList可选配置
            如果配置了parseList,只有在parseList范围内并且不再ignoreList内的sql才会被解析和修改
        -->
        <ignoreList>
            <value>xxx.xxx</value>
        </ignoreList>
        <parseList>
            <value>xxx.dao.UserMapper.insertSelective</value>
            <value>xxx.dao.UserMapper.selectByPrimaryKey</value>
            <value>xxx.UserMapper.updateByPrimaryKeySelective</value>
        </parseList>
        <!--
            配置分表策略
            tableName指的是实际的表名，strategyClass对应的分表策略实现类
        -->
        <strategy tableName="location" strategyClass="xxx.DeviceShardStrategyImpl"/>
    </shardingConfig>

并在项目的mybatis-config.xml里声明使用这个插件，比如

<?xml version="1.0" encoding="UTF-8" ?>
    <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd">

    <configuration>
        <plugins>
            <plugin interceptor="com.google.code.shardbatis.plugin.ShardPlugin">
                <property name="shardingConfig" value="shard-config.xml"/>
            </plugin>
        </plugins>
    </configuration>

5.实现分表策略

就是完成上面strategyClass对应的分表策略实现类，其实只需要实现ShardStrategy接口并实现其中的getTargetTableName方法即可，比如：

public class DeviceShardStrategyImpl implements ShardStrategy {

        private final static int tableCount = 5;
        /**
         * 得到实际表名
         * @param baseTableName 逻辑表名,一般是没有前缀或者是后缀的表名
         * @param params mybatis执行某个statement时使用的参数
         * @param mapperId mybatis配置的statement id
         * @return
         */
        @Override
        public String getTargetTableName(String baseTableName, Object params, String mapperId) {
            // TODO: 需要根据实际的参数或其他（比如当前时间）计算出一个满足要求的值
            int value = 2;
            try {
                int index = value % tableCount + 1;
                String strIndex = "0" + index;
                return baseTableName + "_" + strIndex;
            } catch (Exception e) {
                throw new RuntimeException(e.getMessage(), e);
            }
        }
    }

实际中实现需要根据实际的参数或其他（比如当前时间）计算出一个满足要求的值，最后拼接成实际的表名就可以了。当然了，这个【满足要求的值】有时要计算起来会特别麻烦。这里呢，说一说我自己在实际项目中计算value的一个设计和实现。

实际业务讲解

假设有1000辆被客户使用的共享汽车，假设每辆车每天跑4个小时，每3S一条定位数据，那样一天下来定位数据在60*60*4*1000/3=480w这个量级，实际存储的数据在350w~450w之间，这些数据都需要插入到数据库中。我们知道对于一般的数据库而言，单表达到百万甚至千万级别时，任何操作即使是select count(1)也会变得很慢，这时分表是必须的。

具体说一下分表的策略：假设我们要把原来的大表拆分成512张小表，以设备为维度进行水平拆分，每次对表执行插入时，找到对应的设备(设备表t_device，设备和车辆是一对一) 的 id，使用设备id%512作为表后缀。

举个例子，车辆的定位数据存储的表为t_location_000 ~ t_location_511（注意不是1~512）, 设备A在t_device表里的id为513，那么A对应的定位数据存储表为：513%512=1 -> t_location_001, 设备B在t_device表里的id为1128，那么B对应的分时数据存储表为：1128%512=104 -> t_location_104。相信这个不难理解，接下来的问题就是如何从 public String getTargetTableName(String baseTableName, Object params, String mapperId) 这个方法里取出我们说的t_device A和B了，根据代码上的解释，我们可以知道A和B要从 Object params 里解析出来。

注意，接下来是重点！！！

为了尽可能通用，我们自定义一个注解，@DeviceShard

@Retention(RetentionPolicy.RUNTIME)
    @Target({ElementType.PARAMETER})
    public @interface DeviceShard {
        String value() default "";
    }

分表策略使用的参数要求必须使用这个，比如：

 int insertSelective(@DeviceShard String instrumentId, @Param("timeTrend")TimeTrend record);

接下来增加一个根据Object params解析标识有@DeviceShard注解的参数的实际值，直接给出代码：

public class DeviceShardValue {
        private DeviceShardValue() {}

        public static Object[] getShardValue(Object params, String mapperId) throws Exception {

            if(params != null && StringUtils.isNotBlank(mapperId)) {
                int lastPoint = mapperId.lastIndexOf(".");
                String clazzName = mapperId.substring(0,lastPoint);
                String methodName = mapperId.substring(lastPoint + 1);
                Class clazz = Class.forName(clazzName);
                Method[] methods = clazz.getMethods();

                if (methods.length <= 0){
                    throw new Exception("class has no method!");
                }

                List<Integer> shardFieldIndexes = new ArrayList<>();
                List<Class> shardFieldTypes = new ArrayList<>();
                List<SymbolShard> fieldAnnotations = new ArrayList<>();

                for (Method method : methods) {
                    if (methodName.equals(method.getName())) {
                        Annotation[][] annotations = method.getParameterAnnotations();
                        if(annotations == null || annotations.length <= 0){
                            throw new Exception("method has no shard field");
                        }
                        for (int i = 0; i < annotations.length; i++){
                            Annotation[] fieldAnno = annotations[i];
                            if (fieldAnno != null && fieldAnno.length > 0) {
                                for (Annotation annotation:fieldAnno) {
                                    if (annotation.annotationType() == SymbolShard.class){
                                        shardFieldIndexes.add(i);
                                        shardFieldTypes.add(method.getParameterTypes()[i]);
                                        fieldAnnotations.add((SymbolShard)annotation);
                                    }
                                }
                            }
                        }
                    }
                }
                if (shardFieldIndexes.size() <= 0){
                    throw new Exception("method has no shard field");
                }

                Object[] values = new Object[shardFieldIndexes.size()];
                for (int i = 0; i < shardFieldIndexes.size(); i++){
                    int shardFieldIndex = shardFieldIndexes.get(i);
                    Class shardFieldType = shardFieldTypes.get(i);
                    DeviceShard fieldAnnotation = fieldAnnotations.get(i);
                    if (params.getClass() == shardFieldType) {
                        values[i] = getFieldValue(fieldAnnotation,params);
                    } else {
                        String key = "param" + (shardFieldIndex+1);
                        HashMap<String,Object> map = (HashMap<String,Object>) params;
                        Object tmp = map.get(key);
                        values[i] = getFieldValue(fieldAnnotation, tmp);
                    }
                }

                return values;
            }

            return null;
        }

        private static Object getFieldValue(JmxShard fieldAnnotation,Object params) throws Exception {
            if(isBasicType(params)) {
                return params;
            } else {
                String shardFieldName = fieldAnnotation.value();
                if(StringUtils.isBlank(shardFieldName)) {
                    throw new Exception("the shardFieldName was not annotated");
                }
                Field field = null;
                try {
                    field = params.getClass().getDeclaredField(shardFieldName);
                } catch (NoSuchFieldException e){
                    field = params.getClass().getSuperclass().getDeclaredField(shardFieldName);
                }
                field.setAccessible(true);
                return field.get(params);
            }
        }

        private static boolean isBasicType(Object param){
            if (param == null){
                return false;
            }
            if (param instanceof String){
                return true;
            }
            if (param instanceof BigDecimal){
                return true;
            }
            if (param instanceof Integer){
                return true;
            }
            if (param instanceof Long){
                return true;
            }
            if (param instanceof Double){
                return true;
            }
            if (param instanceof Float){
                return true;
            }
            if (param instanceof Character){
                return true;
            }
            if (param instanceof Byte){
                return true;
            }
            if (param instanceof Short){
                return true;
            }
            if (param instanceof Boolean){
                return true;
            }
            return false;
        }
    }

接下来去实现ShardStrategy就很容易了（个别细节忽略）：

public class TimeTrendShardStrategyImpl implements ShardStrategy{

        private final static Integer tableCount = 512;

        @Override
        public String getTargetTableName(String baseTableName, Object params,String mapperId) {
            Object value;
            try {
                // 调用封装的工具类获取传入标识有@SymbolShard注解的参数的值
                value = DeviceShardValue.getShardValue(params, mapperId)[0];

                // 连接数据库，去symbols表查询，注意这里不是使用自动注入@Autowired和@Resource，这种方式在权限课程里介绍过
                String device = value.toString();
                Device deviceInstance = SpringContextHolder.getBean(DeviceMapper.class).selectByDevice(device);
                if(symbolInstance == null) { // 如果查不到对应的symbol实例, 则返回一个普通表,否则这里会抛一个上层不知道的异常
                    return baseTableName + "_000";
                }

                // 根据id拼装实际的分表后的表名
                Integer index = deviceInstance.getId() % tableCount;
                String strIndex = "";
                if(index < 10) {
                    strIndex = "00" + index;
                } else if(index < 100) {
                    strIndex = "0" + index;
                } else {
                    strIndex = "" + index;
                }
                return baseTableName + "_" + strIndex;
            } catch (Exception e) {
                throw new RuntimeException(e.getMessage(), e);
            }
        }
    }

写到这里，再提醒一下，别忘了把分表的方法和分表策略写入shard_config.xml

6.适用范围

还要注意这个插件的适用范围，我自己在上面踩过坑，就是在做数据库批量操作时使用这个插件会没有效果。

具体支持哪些sql呢，网上有人给了总结，我直接引用一下：

select * from test_table1
    select * from test_table1 where col_1=''
    select * from test_table1 where col_1='' and col_2=8
    select * from test_table1 where col_1=?
    select col_1,max(col_2) from test_table1 where col_4='t1' group by col_1
    select col_1,col_2,col_3 from test_table1 where col_4='t1' order by col_1
    select col_1,col_2,col_3 from test_table1 where id in (?,?,?,?,?,?,?,?,?) limit ?,?
    select a.*  from test_table1 a,test_table2 b where a.id=b.id and a.type='xxxx'
    select a.col_1,a.col_2,a.col_3 from test_table1 a where a.id in (select aid from test_table2 where col_1=1 and col_2=?) order by id desc
    select col_1,col_2 from test_table1 where type is not null and col_3 is null order by id
    select count(*),col_1 from test_table2 group by col_1 having count(*)>1
    select a.col_1,a.col_2,b.col_1 from test_table1 a,t_table b where a.id=b.id
    insert into test_table1 (col_1,col_2,col_3,col_4) values (?,?,?,?)
    SELECT EMPLOYEEIDNO FROM test_table1 WHERE POSITION = 'Manager' AND SALARY > 60000 OR BENEFITS > 12000
    SELECT EMPLOYEEIDNO FROM test_table1 WHERE POSITION = 'Manager' AND (SALARY > 50000 OR BENEFIT > 10000)
    SELECT EMPLOYEEIDNO FROM test_table1 WHERE LASTNAME LIKE 'L%'
    SELECT DISTINCT SELLERID, OWNERLASTNAME, OWNERFIRSTNAME FROM test_table1, test_table2 WHERE SELLERID = OWNERID ORDER BY OWNERLASTNAME, OWNERFIRSTNAME, OWNERID
    SELECT OWNERFIRSTNAME, OWNERLASTNAME FROM test_table1 WHERE EXISTS (SELECT * FROM test_table2 WHERE ITEM = ?)
    SELECT BUYERID, ITEM FROM test_table1 WHERE PRICE >= ALL (SELECT PRICE FROM test_table2)
    SELECT BUYERID FROM test_table1 UNION SELECT BUYERID FROM test_table2
    SELECT OWNERID, 'is in both Orders & Antiques' FROM test_table1 a, test_table2 b WHERE a.OWNERID = b.BUYERID and a.type in (?,?,?)
    SELECT DISTINCT SELLERID, OWNERLASTNAME, OWNERFIRSTNAME FROM test_table1, noconvert_table WHERE SELLERID = OWNERID ORDER BY OWNERLASTNAME, OWNERFIRSTNAME, OWNERID
    SELECT a.* FROM test_table1 a, noconvert_table b WHERE a.SELLERID = b.OWNERID
    update test_table1 set col_1=123 ,col_2=?,col_3=? where col_4=?
    update test_table1 set col_1=?,col_2=col_2+1 where id in (?,?,?,?)
    delete from test_table2 where id in (?,?,?,?,?,?) and col_1 is not null
    INSERT INTO test_table1 VALUES (21, 01, 'Ottoman', ?,?)
    INSERT INTO test_table1 (BUYERID, SELLERID, ITEM) VALUES (01, 21, ?)

可能有些sql语句没有出现在测试用例里，但是相信基本上常用的查询sql shardbatis解析都没有问题，因为shardbatis对sql的解析是基于jsqlparser的

另外需要注意的是：

• 2.0版本中insert update delete 语句中的子查询语句中的表不支持sharding
• select语句中如果进行多表关联，请务必为每个表名加上别名 例如原始sql语句：SELECT a. FROM ANTIQUES a,ANTIQUEOWNERS b, mytable c where a.id=b.id and b.id=c.id 经过转换后的结果可能为：SELECT a. FROM ANTIQUES_0 AS a, ANTIQUEOWNERS_1 AS b, mytable_1 AS c WHERE a.id = b.id AND b.id = c.id