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SpringBoot分库分表

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方案:可以使用拦截器拦截mybatis框架,在执行SQL前对SQL语句根据路由字段进行分库分表操作,下例只做分表功能

@Intercepts:申明需要拦截的方法

拦截StatementHandler对象

一、statementHandler对象的定义

首先我们先来看看statementHandler接口的定义:

首先约定文中将的四大对象是指:executor, statementHandler,parameterHandler,resultHandler对象。

讲到statementHandler,毫无疑问它是我们四大对象最重要的一个,它的任务就是和数据库对话。在它这里会使用parameterHandler和ResultHandler对象为我们绑定SQL参数和组装最后的结果返回。 

public interface StatementHandler {  
  Statement prepare(Connection connection)  
      throws SQLException;  
  
  void parameterize(Statement statement)  
      throws SQLException;  
  
  void batch(Statement statement)  
      throws SQLException;  
  
  int update(Statement statement)  
      throws SQLException;  
  
  <E> List<E> query(Statement statement, ResultHandler resultHandler)  
      throws SQLException;  
  
  BoundSql getBoundSql();    
  ParameterHandler getParameterHandler();    
}  

二、prepare方法

1、首先prepare方法是用来编译SQL

让我们看看它的源码实现。这里我们看到了BaseStatementHandler对prepare方法的实现

@Override  
public Statement prepare(Connection connection) throws SQLException {  
    ErrorContext.instance().sql(boundSql.getSql());  
    Statement statement = null;  
    try {  
    	statement = instantiateStatement(connection);  
    	setStatementTimeout(statement);  
    	setFetchSize(statement);  
   	    return statement;  
    } catch (SQLException e) {  
   		closeStatement(statement);  
    	throw e;  
    } catch (Exception e) {  
    	closeStatement(statement);  
    	throw new ExecutorException("Error preparing statement.  Cause: " + e, e);  
	}  
}  
 
protected abstract Statement instantiateStatement(Connection connection) throws SQLException;  

显然我们通过源码更加关注抽象方法instantiateStatement是做了什么事情。它依旧是一个抽象方法,那么它就有其实现类。

2、那就是之前说的那几个具体的StatementHandler对象

让我们看看PreparedStatementHandler:

 
@Override  
  protected Statement instantiateStatement(Connection connection) throws SQLException {  
      String sql = boundSql.getSql();  
      if (mappedStatement.getKeyGenerator() instanceof Jdbc3KeyGenerator) {  
      	  String[] keyColumnNames = mappedStatement.getKeyColumns();  
	      if (keyColumnNames == null) {  
	          return connection.prepareStatement(sql, PreparedStatement.RETURN_GENERATED_KEYS);  
	      } else {  
	          return connection.prepareStatement(sql, keyColumnNames);  
	      }  
      } else if (mappedStatement.getResultSetType() != null) {  
          return connection.prepareStatement(sql, mappedStatement.getResultSetType().getValue(), ResultSet.CONCUR_READ_ONLY);  
      } else {  
          return connection.prepareStatement(sql);  
      }  
  }   

好这个方法非常简单,我们可以看到它主要是根据上下文来预编译SQL,这是我们还没有设置参数。设置参数的任务是交由,statement接口的parameterize方法来实现的。

3、parameterize方法

上面我们在prepare方法里面预编译了SQL。那么我们这个时候希望设置参数。在Statement中我们是使用parameterize方法进行设置参数的。

让我们看看PreparedStatementHandler中的parameterize方法:

@Override  
  public void parameterize(Statement statement) throws SQLException {  
    parameterHandler.setParameters((PreparedStatement) statement);  
  }  

很显然这里很简单是通过parameterHandler来实现的,我们这篇文章只是停留在statementhandler的程度,等我们讲解parameterHandler的时候再来看它如何实现吧,期待一下吧。

4、query/update方法

我们用了prepare方法预编译了SQL,用了parameterize方法设置参数,那么我们接下来肯定是想执行SQL,而SQL无非是两种:

一种是进行查询——query,另外就是更新——update。

这些方法都很简单,让我们看看PreparedStatementHandler的实现:

@Override  
  public int update(Statement statement) throws SQLException {  
      PreparedStatement ps = (PreparedStatement) statement;  
      ps.execute();  
      int rows = ps.getUpdateCount();  
      Object parameterObject = boundSql.getParameterObject();  
      KeyGenerator keyGenerator = mappedStatement.getKeyGenerator();  
      keyGenerator.processAfter(executor, mappedStatement, ps, parameterObject);  
      return rows;  
  }    
 
  @Override  
  public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {  
      PreparedStatement ps = (PreparedStatement) statement;  
      ps.execute();  
      return resultSetHandler.<E> handleResultSets(ps);  
  }  

例:动态替换SQL中@TableID标识符

package com.study.demo.interceptor;
import com.study.demo.exception.BaseException;
import org.apache.ibatis.executor.statement.StatementHandler;
import org.apache.ibatis.mapping.BoundSql;
import org.apache.ibatis.plugin.Interceptor;
import org.apache.ibatis.plugin.Intercepts;
import org.apache.ibatis.plugin.Invocation;
import org.apache.ibatis.plugin.Plugin;
import org.apache.ibatis.plugin.Signature;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Component;
import org.springframework.util.CollectionUtils;
import java.lang.reflect.Field;
import java.sql.Connection;
import java.util.Map;
import java.util.Properties;
import java.util.Set;
@Component
@Intercepts({
        @Signature(type = StatementHandler.class, method = "prepare", args = {Connection.class, Integer.class})})
public class DynamicSQLInterceptor implements Interceptor {
    private static final Logger LOGGER = LoggerFactory.getLogger(DynamicSQLInterceptor.class);
    private static final String SHARD_TABLE_ID = "SHARD_TABLE_ID";
    private static final String DEFAULT_TABLE_ID = "000";
    @Override
    @SuppressWarnings("unchecked")
    public Object intercept(Invocation invocation) throws Throwable {
        LOGGER.info("DynamicSQLInterceptor.intercept() exec.");
        StatementHandler statementHandler = (StatementHandler) invocation.getTarget();
        Object parameter = statementHandler.getParameterHandler().getParameterObject();
        Map<String, Object> params = (Map)parameter;
        if(CollectionUtils.isEmpty(params)){
            throw new BaseException("SQL: 路由字段不能为空!");
        }
        String tableId = DEFAULT_TABLE_ID;
        Set<String> keySet = params.keySet();
        for (String key : keySet) {
            if (SHARD_TABLE_ID.equals(key)) {
                tableId = String.valueOf(params.get(key));
            }
        }
        BoundSql boundSql = statementHandler.getBoundSql();
        //获取到原始sql语句
        String sql = boundSql.getSql();
        String newSql = sql.replaceAll("@TableID", tableId);
        LOGGER.debug("[DynamicSQLInterceptor] Sql:{}", newSql);
        //通过反射修改sql语句
        Field field = boundSql.getClass().getDeclaredField("sql");
        field.setAccessible(true);
        field.set(boundSql, newSql);
        return invocation.proceed();
    }
    @Override
    public Object plugin(Object target) {
        //只拦截Executor对象,减少目标被代理的次数
        if (target instanceof StatementHandler) {
            return Plugin.wrap(target, this);
        } else {
            return target;
        }
    }
    @Override
    public void setProperties(Properties properties) {
        LOGGER.debug("[DynamicSQLInterceptor] SetProperties");
    }
}

示例SQL:

SELECT * FROM ST_CLASS_@TableID WHERE ID = #{id}

service层示例:

@Override
public Objcet queryByPrimaryKey(String id) {
    Map<String, Object> params = DbShardUtils.shardDBParamMap(id);
    params.put("id", id);
    return testDao.queryByPrimaryKey(params);
}

dao层示例:

@Repository
public interface TestDao {
	Object queryByPrimaryKey(Map<String, Object> params);
}
package com.study.demo.utils;
import org.apache.commons.lang3.StringUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.util.HashMap;
import java.util.Map;
/**
 * 分库分表工具类 <br>
 * 返回Map<String, Object>, 含有key:SHARD_TABLE_ID
 */
public class DbShardUtils {
	private static final Logger LOGGER = LoggerFactory.getLogger(DbShardUtils.class);
	private static final String SHARD_TABLE_ID = "SHARD_TABLE_ID";
	/**
	 * 私有构造函数
	 */
	private DbShardUtils() {
	}
	public static Map<String, Object> shardDBParamMap(String id){
		if (StringUtils.isBlank(id)) {
			LOGGER.error("sharding id is null");
		}
		Map<String, Object> paramMap = new HashMap<>();
		paramMap.put(SHARD_TABLE_ID, rout(id));
		return paramMap;
	}
	private static String rout(String id) {
		// 测试
		return "000";
	}
}

以上为个人经验,希望能给大家一个参考,也希望大家多多支持。

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