聊聊ShardingSphere是怎么进行sql重写的

序

本文主要研究一下ShardingSphere进行sql重写的原理

prepareStatement

org/apache/shardingsphere/driver/jdbc/core/connection/ShardingSphereConnection.java

ShardingSphereConnection的prepareStatement创建的是ShardingSpherePreparedStatement

ShardingSpherePreparedStatement

org/apache/shardingsphere/driver/jdbc/core/statement/ShardingSpherePreparedStatement.java

ShardingSpherePreparedStatement继承了AbstractPreparedStatementAdapter，其构造器主要是通过SQLParserEngine解析sql得到SQLStatement，创建DriverExecutor、BatchPreparedStatementExecutor、KernelProcessor、StatementManager；这里即使useServerPrepStmts=true，也不会触发mysql server的prepare操作

executeUpdate

这里executeUpdate会先执行clearPrevious方法，清空statements、parameterSets、generatedValues，然后createExecutionContext，这里有一步是kernelProcessor.generateExecutionContext

KernelProcessor

generateExecutionContext

shardingsphere-infra-context-5.4.0-sources.jar!/org/apache/shardingsphere/infra/connection/kernel/KernelProcessor.java

KernelProcessor的generateExecutionContext方法先创建routeContext，然后执行rewrite，最后执行createExecutionContext

rewrite

rewrite主要是通过SQLRewriteEntry的rewrite方法进行的

SQLRewriteEntry

shardingsphere-infra-rewrite-5.4.0-sources.jar!/org/apache/shardingsphere/infra/rewrite/SQLRewriteEntry.java

SQLRewriteEntry的rewrite方法，先通过createSQLRewriteContext来创建SQLRewriteContext，这里通过decorate方法遍历decorators，挨个执行SQLRewriteContextDecorator的decorate方法；最后通过GenericSQLRewriteEngine或者RouteSQLRewriteEngine进行rewrite

SQLRewriteContextDecorator

org/apache/shardingsphere/infra/rewrite/context/SQLRewriteContextDecorator.java

SQLRewriteContextDecorator定义了decorate方法，它有诸如ShardingSQLRewriteContextDecorator、EncryptSQLRewriteContextDecorator的实现类

EncryptSQLRewriteContextDecorator

org/apache/shardingsphere/encrypt/rewrite/context/EncryptSQLRewriteContextDecorator.java

rewriteParameters是通过ParameterRewriter进行rewrite，主要是修改ParameterBuilder；而具体sql语句的修改则通过sqlTokenGenerators进行

SQLToken

SQLToken它有诸如InsertValuesToken、SubstitutableColumnNameToken、InsertColumnsToken之类的实现类

RouteSQLRewriteEngine

addSQLRewriteUnits是往sqlRewriteUnits添加SQLRewriteUnit，最后translate方法构建SQLRewriteUnit；SQLRewriteUnit包含了更改之后的sql以及对应改动后的参数

useDriverToExecuteUpdate

org/apache/shardingsphere/driver/jdbc/core/statement/ShardingSpherePreparedStatement.java

useDriverToExecuteUpdate方法会执行createExecutionGroupContext(会执行prepare方法)，cacheStatements这里主要是把eachInput.getStorageResource()真正的PrepareStatement赋值到ShardingSpherePreparedStatement的statements变量中，把eachInput.getExecutionUnit().getSqlUnit().getParameters()赋值到parameterSets，然后执行replay方法通过PreparedStatementInvocationReplayer把修改后的变量replay到真正的PrepareStatement 该方法委托给executor.getRegularExecutor().executeUpdate，最后一个参数为callback，即createExecuteUpdateCallback

DriverExecutionPrepareEngine.prepare

org/apache/shardingsphere/infra/executor/sql/prepare/AbstractExecutionPrepareEngine.java

group方法调用遍历SQLUnit执行createExecutionGroup，而后者则执行sqlExecutionUnitBuilder.build；这里databaseConnectionManager.getConnections获取的connection是通过真正driver获取的connection(com.mysql.jdbc.Driver)

PreparedStatementExecutionUnitBuilder

org/apache/shardingsphere/infra/executor/sql/prepare/driver/jdbc/builder/PreparedStatementExecutionUnitBuilder.java

PreparedStatementExecutionUnitBuilder的build方法这里才真正创建PreparedStatement

StatementManager

org/apache/shardingsphere/driver/jdbc/core/statement/StatementManager.java

createStorageResource则是通过connection.prepareStatement来创建真正的PrepareStatement，而此时传入的sql也是经过重写之后的sql

createExecuteUpdateCallback

org/apache/shardingsphere/driver/jdbc/core/statement/ShardingSpherePreparedStatement.java

createExecuteUpdateCallback创建的JDBCExecutorCallback，其executeSQL方法则是通过((PreparedStatement) statement).executeUpdate()来执行，即委托给了真正的PreparedStatement

小结

• ShardingSphereConnection的prepareStatement创建的是ShardingSpherePreparedStatement，它在ShardingSpherePreparedStatement的executeUpdate的时候进行sql重写，然后prepare，最后执行的时候是通过JDBCExecutorCallback，其executeSQL方法则是通过((PreparedStatement) statement).executeUpdate()来执行，即委托给了真正的PreparedStatement
• rewriteParameters是通过ParameterRewriter进行rewrite，主要是修改ParameterBuilder；而具体sql语句的修改则通过sqlTokenGenerators进行
• PreparedStatementExecutionUnitBuilder的build方法这里才真正创建PreparedStatement：它通过StatementManager.createStorageResource则是通过connection.prepareStatement来创建真正的PrepareStatement，而此时传入的sql也是经过重写之后的sql
• useDriverToExecuteUpdate方法会执行createExecutionGroupContext(会执行prepare方法)，cacheStatements这里主要是把eachInput.getStorageResource()真正的PrepareStatement赋值到ShardingSpherePreparedStatement的statements变量中，把eachInput.getExecutionUnit().getSqlUnit().getParameters()赋值到parameterSets，然后执行replay方法通过PreparedStatementInvocationReplayer把修改后的变量replay到真正的PrepareStatement

ShardingSpherePreparedStatement实现了java.sql.PreparedStatement接口，其sql属性是用户传入的sql，即未经过重写的sql，而实际execute的时候，会触发sql重写(包括重写sql语句及参数)，最后会通过connection.prepareStatement(传入重写之后的sql)来创建真正的PrepareStatement，然后有一步replay操作，把重写后的参数作用到真正的PrepareStatement，最后通过((PreparedStatement) statement).executeUpdate()来触发执行 至此我们可以得到sql重写的一个基本思路：通过实现java.sql.PreparedStatement接口伪装一个PreparedStatement类，其创建和set参数先内存缓存起来，之后在execute的时候进行sql重写，创建真正的PreparedStatement，replay参数，执行execute方法