一、前言
其實(shí)最近找工作面試，都能補(bǔ)缺自己好多知識(shí)點(diǎn)，對(duì)于源碼的熟悉度，掌握程度都會(huì)有一個(gè)進(jìn)步，一些問題應(yīng)該怎么思考等等，這就是需要的成長(zhǎng)。努力?。?！
二、內(nèi)容
離職前做了一個(gè)分表的功能，按照月分表處理埋點(diǎn)數(shù)據(jù)，遇到以下兩個(gè)問題
1)、在分表查詢數(shù)據(jù)的時(shí)候，出現(xiàn)異常，Unsupported Date type:class java.lang.String
2）、在分表查詢跨表查的時(shí)候只查詢出來(lái)一條數(shù)據(jù)
現(xiàn)在對(duì)這兩個(gè)問題做下說(shuō)明如下：
2.1、類型轉(zhuǎn)換異常問題
@Override
public Object invoke(Object proxy, Method method, Object[] params) throws Throwable {
try {
if (Object.class.equals(method.getDeclaringClass())) {
return method.invoke(this, params);
}
Object o = method.invoke(rs, params);
if ("next".equals(method.getName())) {
if (((Boolean) o)) {
rows++;
if (isTraceEnabled()) {
ResultSetMetaData rsmd = rs.getMetaData();
final int columnCount = rsmd.getColumnCount();
if (first) {
first = false;
printColumnHeaders(rsmd, columnCount);
}
printColumnValues(columnCount);
}
} else {
debug(" Total: " + rows, false);
}
}
clearColumnInfo();
return o;
} catch (Throwable t) {
throw ExceptionUtil.unwrapThrowable(t);
}
}
private void printColumnValues(int columnCount) {
StringBuilder row = new StringBuilder();
row.append(" Row: ");
for (int i = 1; i <= columnCount; i++) {
String colname;
try {
if (blobColumns.contains(i)) {
colname = "<<BLOB>>";
} else {
colname = rs.getString(i);
}
} catch (SQLException e) {
// generally can't call getString() on a BLOB column
colname = "<<Cannot Display>>";
}
row.append(colname);
if (i != columnCount) {
row.append(", ");
}
}
trace(row.toString(), false);
}
image.png
@Override
public String getString(final int columnIndex) throws SQLException {
Object result = mergeResultSet.getValue(columnIndex, String.class);
wasNull = null == result;
return (String) ResultSetUtil.convertValue(result, String.class);
}
image.png
image.png
### Cause: com.dangdang.ddframe.rdb.sharding.exception.ShardingJdbcException: Unsupported Date type:class java.lang.String
at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:30)
at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:150)
at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:141)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:433)
... 89 common frames omitted
Caused by: com.dangdang.ddframe.rdb.sharding.exception.ShardingJdbcException: Unsupported Date type:class java.lang.String
at com.dangdang.ddframe.rdb.sharding.merger.util.ResultSetUtil.convertDateValue(ResultSetUtil.java:122)
at com.dangdang.ddframe.rdb.sharding.merger.util.ResultSetUtil.convertValue(ResultSetUtil.java:56)
at com.dangdang.ddframe.rdb.sharding.jdbc.core.resultset.ShardingResultSet.getString(ShardingResultSet.java:168)
at org.apache.ibatis.logging.jdbc.ResultSetLogger.printColumnValues(ResultSetLogger.java:117)
at org.apache.ibatis.logging.jdbc.ResultSetLogger.invoke(ResultSetLogger.java:79)
at com.sun.proxy.$Proxy172.next(Unknown Source)
at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.handleRowValuesForSimpleResultMap(DefaultResultSetHandler.java:345)
at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.handleRowValues(DefaultResultSetHandler.java:322)
at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.handleResultSet(DefaultResultSetHandler.java:295)
at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.handleResultSets(DefaultResultSetHandler.java:192)
at org.apache.ibatis.executor.statement.PreparedStatementHandler.query(PreparedStatementHandler.java:64)
at org.apache.ibatis.executor.statement.RoutingStatementHandler.query(RoutingStatementHandler.java:79)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.apache.ibatis.plugin.Plugin.invoke(Plugin.java:63)
at com.sun.proxy.$Proxy169.query(Unknown Source)
at org.apache.ibatis.executor.ReuseExecutor.doQuery(ReuseExecutor.java:60)
at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:324)
at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:156)
at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:109)
at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:83)
at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:148)
... 95 common frames omitted
ResultSetLogger.java ----- invoke(Object proxy,Method method,Object[] params) throws Throwable
ResultSetLogger.java ----- printColumnValues(columnCount);
ResultSetLogger.java ----- colname = rs.getString(i);
ShardingResultSet.java ----- getString(final int columnIndex);
ShardingResultSet.java ----- return (String) ResultSetUtil.convertValue(result, String.class);
ResultSetUtil.java ----- return convertDateValue(value, convertType);
ResultSetUtil.java convertDateValue(final Object value, final Class<?> convertType) 拋出異常
image.png
2.2、對(duì)于查詢數(shù)據(jù)合并的問題
針對(duì)第二個(gè)問題，最開始思考的時(shí)候是覺得是不是sharding不支持跨庫(kù)查詢，因?yàn)閱渭儾樵円粡埍硎菦]問題的，所有也沒辦法，就是跟源碼，在對(duì)于一列的時(shí)候count的時(shí)候，進(jìn)行了合并操作，其實(shí)當(dāng)時(shí)很納悶，為什么，count這個(gè)字段有影響么，然后我嘗試在sql里面把如下代碼做了更改
原始sql:
select count,clickDate,clickName from table
修改完后
select t.count,t.clickDate,t.clickName from table t
其實(shí)就是給表加了個(gè)別名，然后也加到了字段前，這樣就解決了，其實(shí)覺得很神奇，后面把這的源碼那塊放出來(lái)，之前忘記截圖了。
