Why batchUpdate return int[][] instead of int[] 2016-03-28 01:26
There are multiple batchUpdate methods in JdbcTemplate. I found most of them return int[]. Only one method with ParameterizedPreparedStatementSetter parameter return int[][] instead of int[]. It makes me wonder. int[] means the number of rows affected by each statement. int[] is enough why use int[][].
The source code is here
if (logger.isDebugEnabled()) {
logger.debug("Executing SQL batch update [" + sql + "] with a batch size of " + batchSize);
}
return execute(sql, new PreparedStatementCallback<int[][]>() {
@Override
public int[][] doInPreparedStatement(PreparedStatement ps) throws SQLException {
List<int[]> rowsAffected = new ArrayList<int[]>();
try {
boolean batchSupported = true;
if (!JdbcUtils.supportsBatchUpdates(ps.getConnection())) {
batchSupported = false;
logger.warn("JDBC Driver does not support Batch updates; resorting to single statement execution");
}
int n = 0;
for (T obj : batchArgs) {
pss.setValues(ps, obj);
n++;
if (batchSupported) {
ps.addBatch();
if (n % batchSize == 0 || n == batchArgs.size()) {
if (logger.isDebugEnabled()) {
int batchIdx = (n % batchSize == 0) ? n / batchSize : (n / batchSize) + 1;
int items = n - ((n % batchSize == 0) ? n / batchSize - 1 : (n / batchSize)) * batchSize;
logger.debug("Sending SQL batch update #" + batchIdx + " with " + items + " items");
}
rowsAffected.add(ps.executeBatch());
}
}
else {
int i = ps.executeUpdate();
rowsAffected.add(new int[] {i});
}
}
int[][] result = new int[rowsAffected.size()][];
for (int i = 0; i < result.length; i++) {
result[i] = rowsAffected.get(i);
}
return result;
} finally {
if (pss instanceof ParameterDisposer) {
((ParameterDisposer) pss).cleanupParameters();
}
}
}
});
We can see the most important code is rowsAffected.add(ps.executeBatch());. If JDBC Driver support batchUpdate JdbcTemplate will invoke executeBatch() method or JdbcTemplate will execute statement one by one(I call it fake batchUpdate). executeBatch() will return int[] but executeUpdate() will return int. So this batchUpdate method return int[][] to apply to both cases. In other words different result will prove the JDBC Driver support batch update or not.
Summary
If the JDBC Driver support "batch update" the result will be like following
[[1, 1, 1]]
if the JDBC Driver not support "batch update" the result will be like following
[[1], [1], [1]]