spring +mybatis read-write separation

1. Configure and define database connection properties

2. Define bean
<!-- Master database connection pool -->
    <bean id="masterDataSource" parent="abstractDataSource">
        <property name="url" value="${master.jdbc .url}"/>
        <property name="username" value="${master.jdbc.username}"/>
        <property name="password" value="${master.jdbc.password}"/>
    </ bean>

    <!-- From database connection pool 1 -->
    <bean id="slave1DataSource" parent="abstractDataSource">
        <property name="url" value="${slave1.jdbc.url}"/>
        <property name="username" value="${slave1.jdbc.username}"/>
        <property name="password" value="${slave1.jdbc.password}"/>
    </bean>

    <!-- From database connection pool 2 -->
    <bean id="slave2DataSource" parent="abstractDataSource">
        <property name="url" value="${slave2.jdbc.url}"/>
        <property name="username" value="${slave2.jdbc.username}"/>
        <property name="password" value="${slave2.jdbc.password}"/>
    </bean>

    <!-- 从数据库连接池3 -->
    <bean id="slave3DataSource" parent="abstractDataSource">
        <property name="url" value="${slave3.jdbc.url}"/>
        <property name="username" value="${slave3.jdbc.username}"/>
        <property name="password" value="${slave3.jdbc.password}"/>     <bean id="dynamicDataSource" class="com.common.datasource.DynamicDataSource">     <!-- Dynamically switch data sources-->
    </bean>



        <property name="writeDataSource"  ref="masterDataSource"></property>
        <property name="readDataSources">
            <list>
                <ref bean="slave1DataSource" />
                <ref bean="slave2DataSource" />
                <ref bean="slave3DataSource" />
            </list>
        </property>
        <!--轮询方式-->
        <property name="readDataSourcePollPattern" value="1" />
        <property name="onlyWrite" value="true" />
    </bean>

三、事务定义
<!-- 事务管理器 -->
    <bean id="dynamicTransactionManager" class="com.common.datasource.DynamicDataSourceTransactionManager">
        <property name="dataSource" ref="dynamicDataSource"/>
    </bean>

    <tx:annotation-driven transaction-manager="dynamicTransactionManager"/>

Fourth, configure the plugin
<!-- Configure the paging plugin-->
    <plugins>
        <plugin interceptor="com.common.datasource.DynamicPlugin" />
        <plugin interceptor="com.github.pagehelper.PageHelper">
            <!-- Set the database type Oracle, Mysql, MariaDB, SQLite, Hsqldb, PostgreSQL six kinds of databases -->
            <property name="dialect" value="mysql"/>
        </plugin>
    </plugins>

5. Write a dynamic data source class
public class DynamicDataSource extends AbstractRoutingDataSource {

    private static final Long MAX_POOL = Long.MAX_VALUE;
    private final Lock lock = new ReentrantLock();
    private Object writeDataSource; //write data source
    private List<Object> readDataSources; //multiple read data sources
    private int readDataSourceSize; //read data source number
    private int readDataSourcePollPattern = 0; //Get the read data source method, 0: random, 1: polling
    private AtomicLong counter = new AtomicLong(0);
    private boolean onlyWrite=false;

    @Override
    public void afterPropertiesSet() {
        if (this.writeDataSource == null) {
            throw new IllegalArgumentException("Property 'writeDataSource' is required");
        }
        setDefaultTargetDataSource(writeDataSource);
        Map<Object, Object> targetDataSources = new HashMap< >();
        targetDataSources.put(DynamicDataSourceGlobal.WRITE.name(), writeDataSource);
        if (readDataSources != null) {
            for (int i = 0; i < readDataSources.size(); i++) {
                targetDataSources.put(DynamicDataSourceGlobal.READ.name() + i, readDataSources.get(i));
            }
            readDataSourceSize = readDataSources.size();
        } else {
            readDataSourceSize = 0;
        }
        setTargetDataSources(targetDataSources);
        super.afterPropertiesSet();
    }

    @Override
    protected Object determineCurrentLookupKey() {
        if (onlyWrite){
            return DynamicDataSourceGlobal.WRITE.name();
        }
        DynamicDataSourceGlobal dynamicDataSourceGlobal = DynamicDataSourceHolder.getDataSource();
        if (dynamicDataSourceGlobal == null || dynamicDataSourceGlobal == DynamicDataSourceGlobal.WRITE || readDataSourceSize <= 0) {
            return DynamicDataSourceGlobal.WRITE.name();
        }
        //index表示选择第几个从数据库
        int index;
        if(readDataSourcePollPattern == 1) {
            //轮询方式
            long currValue = counter.incrementAndGet();
            if((currValue + 1) >= MAX_POOL) {
                try {
                    lock.lock();
                    if((currValue + 1) >= MAX_POOL) {
                        counter.set(0);
                    }
                } finally {
                    lock.unlock();
                }
            }
            index = (int) (currValue % readDataSourceSize);
        } else {
            //随机方式
            index = ThreadLocalRandom.current().nextInt(0, readDataSourceSize);
        }
        return dynamicDataSourceGlobal.name() + index;
    }
    public void setWriteDataSource(Object writeDataSource) {
        this.writeDataSource = writeDataSource;
    }

    public List<Object> getReadDataSources() {
        return readDataSources;
    }

    public void setReadDataSources(List<Object> readDataSources) {
        this.readDataSources = readDataSources;
    }

    public Object getWriteDataSource() {
        return writeDataSource;
    }

    public int getReadDataSourceSize() {
        return readDataSourceSize;
    }

    public void setReadDataSourceSize(int readDataSourceSize) {
        this.readDataSourceSize = readDataSourceSize;
    }

    public int getReadDataSourcePollPattern() {
        return readDataSourcePollPattern;
    }

    public void setReadDataSourcePollPattern(int readDataSourcePollPattern) {
        this.readDataSourcePollPattern = readDataSourcePollPattern;
    }

    public boolean isOnlyWrite() {
        return onlyWrite;
    }

    public void setOnlyWrite(boolean onlyWrite) {
        this.onlyWrite = onlyWrite;
    }
}


public class DynamicDataSourceHolder {
    private static final ThreadLocal<DynamicDataSourceGlobal> holder = new ThreadLocal<DynamicDataSourceGlobal>();

    private DynamicDataSourceHolder() {
        //
    }

    public static void putDataSource(DynamicDataSourceGlobal dataSource) {
        holder.set(dataSource);
    }

    public static DynamicDataSourceGlobal getDataSource() {
        return holder.get();
    }

    public static void clearDataSource() {
        holder.remove();
    }
}

public class DynamicDataSourceTransactionManager extends DataSourceTransactionManager {

    /**
     * read only Transaction to read library, read and write transaction to write library
     *
     * @param transaction
     * @param definition
     */
    @Override
    protected void doBegin(Object transaction, TransactionDefinition definition) {

        //Set data source
        boolean readOnly = definition.isReadOnly();
        if (readOnly) {
            DynamicDataSourceHolder.putDataSource(DynamicDataSourceGlobal.READ);
        } else {
            DynamicDataSourceHolder.putDataSource(DynamicDataSourceGlobal.WRITE);
        }
        super.doBegin(transaction, definition);
    }

    /**
     * clean up thread local data source
     *
     * @ param transaction
     */
    @Override
    protected void doCleanupAfterCompletion(Object transaction) {
        super.doCleanupAfterCompletion(transaction);
        DynamicDataSourceHolder.clearDataSource();
    }
}

/**
* Desc: Mybatis dynamic database switch plugin
*/
@Intercepts({
        @Signature(type = Executor.class, method = "update", args = {
                MappedStatement.class, Object.class}),
        @Signature(type = Executor.class, method = "query", args = {
                MappedStatement.class, Object.class, RowBounds.class,
                ResultHandler.class})})
public class DynamicPlugin implements Interceptor {

    protected static final Logger logger = LoggerFactory.getLogger(DynamicPlugin.class);

    private static final String REGEX = ".*insert\\u0020.*|.*delete\\u0020.*|.*update\\u0020.*";

    private static final Map<String, DynamicDataSourceGlobal> cacheMap = new ConcurrentHashMap<>();

    @Override
    public Object intercept(Invocation invocation) throws Throwable {

        boolean synchronizationActive = TransactionSynchronizationManager.isSynchronizationActive();
        if (!synchronizationActive) {
            Object[] objects = invocation.getArgs();
            MappedStatement ms = (MappedStatement) objects[0];
            DynamicDataSourceGlobal dynamicDataSourceGlobal;

            if ((dynamicDataSourceGlobal = cacheMap.get(ms.getId())) == null) {
                //读方法
                if (ms.getSqlCommandType().equals(SqlCommandType.SELECT)) {
                    //!selectKey 为自增id查询主键(SELECT LAST_INSERT_ID() )方法，使用主库
                    if (ms.getId().contains(SelectKeyGenerator.SELECT_KEY_SUFFIX)) {
                        dynamicDataSourceGlobal = DynamicDataSourceGlobal.WRITE;
                    } else {
                        BoundSql boundSql = ms.getSqlSource().getBoundSql(objects[1]);
                        String sql = boundSql.getSql().toLowerCase(Locale.CHINA).replaceAll("[\\t\\n\\r]", " ");
                        if (sql.matches(REGEX)) {
                            dynamicDataSourceGlobal = DynamicDataSourceGlobal.WRITE;
                        } else {
                            dynamicDataSourceGlobal = DynamicDataSourceGlobal.READ;
                        }
                    }
                } else {
                    dynamicDataSourceGlobal = DynamicDataSourceGlobal.WRITE;
                }
                logger.warn("设置方法[{}] use [{}] Strategy, SqlCommandType [{}]..", ms.getId(), dynamicDataSourceGlobal.name(), ms.getSqlCommandType().name());
                cacheMap.put(ms.getId(), dynamicDataSourceGlobal);
            }
            DynamicDataSourceHolder.putDataSource(dynamicDataSourceGlobal);
        }

        return invocation.proceed();
    }

    @Override
    public Object plugin(Object target) {
        if (target instanceof Executor) {
            return Plugin.wrap(target, this);
        } else {
            return target;
        }
    }

    @Override
    public void setProperties(Properties properties) {
        //
    }