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This article will explain in detail how to use the streaming query about jdbc and mybatis. Xiaobian thinks it is quite practical, so share it with you as a reference. I hope you can gain something after reading this article.

jdbc stream query:

Jdbc's streaming query requires three parameters to be set when generating the Prepared Statement. As follows:

PreparedStatement stmt = jdbcTemplate.getDataSource().getConnection().prepareStatement(sql, ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY);stmt.setFetchSize(Integer.MIN_VALUE);

The main usage is the prepareStatement method of java.sql.Connection.

PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency) throws SQLException;

resultSetType and resultSetConcurrency we want to set to ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY respectively.

Also, fetchSize is set to Integer.MIN_VALUE, and at first I wondered why it was this value. Later, it was discovered that there was a special treatment for this value in the code.

This is the setFetchSize method of com.mysql.cj.jdbc.StatementImpl.

@Override public void setFetchSize(int rows) throws SQLException { synchronized (checkClosed().getConnectionMutex()) { if (((rows

0) && (rows > this.getMaxRows()))) { throw SQLEror.createSQLException(Messages.getString("Statement.7"), MysqlErrorNumbers.SQL_STATE_ILLcom.mysql.cj.jdbc.StatementImpl's method EGAL_ARGUMENT, getExceptionInterceptor()); } this.query.setResultFetchSize(rows); } }

resultSetType, there are three types

/** * The constant indicating the type for a ResultSet object * whose cursor may move only forward. * @since 1.2 */ int TYPE_FORWARD_ONLY = 1003; /** * The constant indicating the type for a ResultSet object * that is scrollable but generally not sensitive to changes to the data * that underlies the ResultSet. * @since 1.2 */ int TYPE_SCROLL_INSENSITIVE = 1004; /** * The constant indicating the type for a ResultSet object * that is scrollable and generally sensitive to changes to the data * that underlies the ResultSet. * @since 1.2 */ int TYPE_SCROLL_SENSITIVE = 1005;stmt = conn.prepareStatement(sql, ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY);stmt.setFetchSize(Integer.MIN_VALUE);

resultSetConcurrency has the following two types, stream query to be set to read-only, data will not be updated.

/** * The constant indicating the concurrency mode for a * ResultSet object that may NOT be updated. * @since 1.2 */ int CONCUR_READ_ONLY = 1007; /** * The constant indicating the concurrency mode for a * ResultSet object that may be updated. * @since 1.2 */ int CONCUR_UPDATABLE = 1008;mybatis Flow Query:

Code in mapper:

@Select("select * from xxx order by xx desc")@Options(resultSetType = ResultSetType.FORWARD_ONLY, fetchSize = Integer.MIN_VALUE)@ResultType(XxxObject.class)void queryStreamResult(ResultHandler handler);

Add comments @Options and @ResultType to query methods. Needless to say, the parameters are set the same as the bottom layer of jdbc above, and the parameter values are the same.

It just sets @ResultType to tell the program what type of object it should return. And this ResultHandler is actually Consumer's functional interface for processing each piece of data returned.

The code in the specific method:

@Override public Boolean dealDataList() { mapper.queryStreamResult(resultContext -> { dealSingleData(resultContext.getResultObject().getUid()); }); return true; }

How to use each returned data here? As long as you use ResultObject in resultContext, you can get the XxxObject object set by the mapper above for operation.

About "jdbc and mybatis streaming query how to use" this article is shared here, I hope the above content can be of some help to everyone, so that you can learn more knowledge, if you think the article is good, please share it for more people to see.

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