路由的輸入與執(zhí)行
ShardingPreparedStatement的route()方法如下，routingEngine在構(gòu)造時(shí)會(huì)傳入需要路由的sql字符串以及對(duì)應(yīng)的Connection關(guān)聯(lián)的ShardingContext（一個(gè)javaBean），在執(zhí)行路由的時(shí)候栏笆，route()方法會(huì)傳入setParameter獲得的參數(shù)僧鲁，根據(jù)參數(shù)、參數(shù)值以及SQL進(jìn)行路由分析產(chǎn)生執(zhí)行單元PreparedStatementUnit列表奈懒，之后將PreparedStatementUnit列表傳到谷歌的Excutor框架去對(duì)里面路由后的各個(gè)SQL通過PreparedStatement執(zhí)行屯阀。
這里的getParameters()實(shí)際上獲取的是父類的屬性，在父類已經(jīng)定義了捅伤，父類是AbstractShardingPreparedStatementAdapter抽象類劫流，再通過幾層關(guān)系實(shí)現(xiàn)了PreparedStatement的接口，ShardingPreparedStatement通過子類繼承的方式封裝并實(shí)現(xiàn)了PreparedStatement接口規(guī)范丛忆，實(shí)現(xiàn)了excuteQuery等方法祠汇，ShardingPreparedStatement的創(chuàng)建在ShardingConnection里進(jìn)行創(chuàng)建
private Collection<PreparedStatementUnit> route() throws SQLException {
Collection<PreparedStatementUnit> result = new LinkedList<>();
routeResult = routingEngine.route(getParameters());
for (SQLExecutionUnit each : routeResult.getExecutionUnits()) {
SQLType sqlType = routeResult.getSqlStatement().getType();
Collection<PreparedStatement> preparedStatements;
if (SQLType.DDL == sqlType) {
preparedStatements = generatePreparedStatementForDDL(each);
} else {
preparedStatements = Collections.singletonList(generatePreparedStatement(each));
}
routedStatements.addAll(preparedStatements);
for (PreparedStatement preparedStatement : preparedStatements) {
replaySetParameter(preparedStatement);
result.add(new PreparedStatementUnit(each, preparedStatement));
}
}
return result;
}
public ShardingPreparedStatement(final ShardingConnection connection, final String sql, final int resultSetType, final int resultSetConcurrency, final int resultSetHoldability) {
this.connection = connection;
this.resultSetType = resultSetType;
this.resultSetConcurrency = resultSetConcurrency;
this.resultSetHoldability = resultSetHoldability;
routingEngine = new PreparedStatementRoutingEngine(sql, connection.getShardingContext());
}
SQL的解析到路由的解析到SQL的執(zhí)行
從ShardingPreparedStatement的route()方法跟進(jìn)下去，可以發(fā)現(xiàn)路由解析的過程是在PreparedStatementRoutingEngine里面蘸际，PreparedStatementRoutingEngine是上面說到的routingEngine的具體實(shí)現(xiàn)座哩，在構(gòu)造他的時(shí)候徒扶，他獲取了sql字符串和Connection連接關(guān)聯(lián)的ShardingContext（一個(gè)javaBean）粮彤，在調(diào)用route()的時(shí)候獲取了PreparedStatement的參數(shù)，因此路由解析的參數(shù)的三個(gè)輸入就確定了下來姜骡；PreparedStatementRoutingEngine里面有三個(gè)屬性以及一個(gè)方法导坟，看到這里，基本上可以確定路由算法就是在SQLRouter接口的實(shí)現(xiàn)類實(shí)現(xiàn)的圈澈，從構(gòu)造方法里面跟進(jìn)去可以發(fā)現(xiàn)SQLRouter的實(shí)現(xiàn)類在2.0版本有兩個(gè)惫周，一個(gè)是DatabaseHintSQLRouter，一個(gè)是ParsingSQLRouter康栈，他們都實(shí)現(xiàn)了SQLRouter的parse和route方法递递，parse解析的結(jié)果封裝在SQLStatement接口，route的結(jié)果封裝在SQLRouteResult（一個(gè)Bean）啥么。DMLStatement繼承AbstractSQLStatement從而實(shí)現(xiàn)SQLStatement接口登舞，DMLStatement根據(jù)SQL的類型派生了例如InsertStatement、updateStatement等子類（alter悬荣、create菠秒、drop、insert氯迂、select践叠、truncate、update）嚼蚀。
實(shí)際上這里的SQLStatement命名應(yīng)該是參考了mysql-connector包里面的禁灼。從下面的代碼 route(final List<Object> parameters)我們也可以知道，sqlStatement封裝的是SQL解析后的結(jié)果轿曙，sqlRouter利用了該結(jié)果去對(duì)SQL進(jìn)行路由弄捕，封裝成SQLRouteResult哮独，最后SQL的執(zhí)行就是利用了SQLRouteResult里面的信息,sqlRouter里面方法的執(zhí)行順序是先parse后route。
public final class PreparedStatementRoutingEngine {
private final String logicSQL;
private final SQLRouter sqlRouter;
private SQLStatement sqlStatement;
public PreparedStatementRoutingEngine(final String logicSQL, final ShardingContext shardingContext) {
this.logicSQL = logicSQL;
sqlRouter = SQLRouterFactory.createSQLRouter(shardingContext);
}
/**
* SQL route.
*
* <p>First routing time will parse SQL, after second time will reuse first parsed result.</p>
*
* @param parameters parameters of SQL placeholder
* @return route result
*/
public SQLRouteResult route(final List<Object> parameters) {
if (null == sqlStatement) {
sqlStatement = sqlRouter.parse(logicSQL, parameters.size());
}
return sqlRouter.route(logicSQL, parameters, sqlStatement);
}
}
