如何使用JDBC从存储过程中获取* everything *

使用JDBC处理sql Server存储过程时,偶尔会遇到两种奇怪的行为：

问题1：我在sql Server Management Studio(SSMS)中运行存储过程并返回结果集.但是,当我尝试

try (CallableStatement cs = conn.prepareCall("{call dbo.TroublesomeSP}")) {
    ResultSet rs = cs.executeQuery();

我得到了例外

com.microsoft.sqlserver.jdbc.sqlServerException: The statement did not return a result set.

问题2：我在SSMS中运行存储过程并引发错误,但是当我使用JDBC来执行存储过程时,不会抛出任何异常.

为什么会出现这些问题？如何避免这些问题？

解决方法:

当我们在JDBC中执行存储过程时,我们会得到一系列零或多个“结果”.然后我们可以通过调用CallableStatement#getMoreResults()来顺序处理这些“结果”.每个“结果”都可以包含

>我们可以使用ResultSet对象检索零行或多行数据,
>我们可以使用CallableStatement#getUpdateCount()检索的DML语句(INSERT,UPDATE,DELETE)的更新计数,或者
>抛出sqlServerException的错误.

对于“问题1”,问题通常是存储过程不以SET NOCOUNT ON开头;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,数据行“卡在它后面”,直到我们调用getMoreResults.

“问题2”基本上是同一个问题.存储过程在错误发生之前产生“结果”(通常是SELECT,或可能是更新计数).错误在后续“结果”中返回,并且在我们使用getMoreResults“检索”它之前不会导致异常.

在许多情况下,只需添加SET NOCOUNT ON即可避免问题;作为存储过程中的第一个可执行语句.但是,对存储过程的更改并不总是可行的,事实仍然是,为了从存储过程中取回所有内容,我们需要继续调用getMoreResults,直到Javadoc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,“魔鬼在细节中”,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

…以下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]");
}

…生成以下控制台输出：

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]