当我们在 JDBC 中执行存储过程时，我们会返回一系列零个或多个“结果”。然后我们可以通过调用顺序处理这些“结果”CallableStatement#getMoreResults()。每个“结果”可以包含
- 我们可以使用以下命令检索零行或多行数据
ResultSet object,
- 我们可以检索的 DML 语句（INSERT、UPDATE、DELETE）的更新计数
CallableStatement#getUpdateCount(), or
- 引发 SQLServerException 的错误。
对于“问题 1”，问题通常是存储过程不以SET NOCOUNT ON;并在执行 SELECT 之前执行 DML 语句以生成结果集。 DML 的更新计数作为第一个“结果”返回，并且数据行“卡在它后面”，直到我们调用getMoreResults.
“问题2”本质上是同样的问题。存储过程在错误发生之前生成一个“结果”（通常是一个 SELECT，或者可能是一个更新计数）。该错误在后续“结果”中返回，并且在我们使用“检索”它之前不会导致异常getMoreResults.
在许多情况下，只需添加即可避免该问题SET NOCOUNT ON;作为存储过程中的第一个可执行语句。然而，对存储过程的更改并不总是可能的，事实仍然是为了获得一切从存储过程返回我们需要继续调用getMoreResults直到，正如 Javadoc 所说：
There are no more results when the following is true:
// stmt is a Statement object
((stmt.getMoreResults() == false) && (stmt.getUpdateCount() == -1))
这听起来很简单，但像往常一样，“细节决定成败”，如下例所示。对于 SQL Server 存储过程...
ALTER PROCEDURE dbo.TroublesomeSP AS
BEGIN
-- note: no `SET NOCOUNT ON;`
DECLARE @tbl TABLE (id VARCHAR(3) PRIMARY KEY);
DROP TABLE NonExistent;
INSERT INTO @tbl (id) VALUES ('001');
SELECT id FROM @tbl;
INSERT INTO @tbl (id) VALUES ('001'); -- duplicate key error
SELECT 1/0; -- error _inside_ ResultSet
INSERT INTO @tbl (id) VALUES ('101');
INSERT INTO @tbl (id) VALUES ('201'),('202');
SELECT id FROM @tbl;
END
...下面的Java代码将返回所有内容...
try (CallableStatement cs = conn.prepareCall("{call dbo.TroublesomeSP}")) {
boolean resultSetAvailable = false;
int numberOfResultsProcessed = 0;
try {
resultSetAvailable = cs.execute();
} catch (SQLServerException sse) {
System.out.printf("Exception thrown on execute: %s%n%n", sse.getMessage());
numberOfResultsProcessed++;
}
int updateCount = -2; // initialize to impossible(?) value
while (true) {
boolean exceptionOccurred = true;
do {
try {
if (numberOfResultsProcessed > 0) {
resultSetAvailable = cs.getMoreResults();
}
exceptionOccurred = false;
updateCount = cs.getUpdateCount();
} catch (SQLServerException sse) {
System.out.printf("Current result is an exception: %s%n%n", sse.getMessage());
}
numberOfResultsProcessed++;
} while (exceptionOccurred);
if ((!resultSetAvailable) && (updateCount == -1)) {
break; // we're done
}
if (resultSetAvailable) {
System.out.println("Current result is a ResultSet:");
try (ResultSet rs = cs.getResultSet()) {
try {
while (rs.next()) {
System.out.println(rs.getString(1));
}
} catch (SQLServerException sse) {
System.out.printf("Exception while processing ResultSet: %s%n", sse.getMessage());
}
}
} else {
System.out.printf("Current result is an update count: %d %s affected%n",
updateCount,
updateCount == 1 ? "row was" : "rows were");
}
System.out.println();
}
System.out.println("[end of results]");
}
...产生以下控制台输出：
Exception thrown on execute: Cannot drop the table 'NonExistent', because it does not exist or you do not have permission.
Current result is an update count: 1 row was affected
Current result is a ResultSet:
001
Current result is an exception: Violation of PRIMARY KEY constraint 'PK__#314D4EA__3213E83F3335971A'. Cannot insert duplicate key in object 'dbo.@tbl'. The duplicate key value is (001).
Current result is a ResultSet:
Exception while processing ResultSet: Divide by zero error encountered.
Current result is an update count: 1 row was affected
Current result is an update count: 2 rows were affected
Current result is a ResultSet:
001
101
201
202
[end of results]
