Common Problems with Parameter and Data Value Handling (Common Problems with Parameter and Data Value Handling) _ Spring Framework6.2.0-SNAPSHOT中文文档(官方文档中文翻译)|Spring 教程 —

This version is still in development and is not considered stable yet. For the latest stable version, please use Spring Framework 6.1.13!spring-doc.cn

Common problems with parameters and data values exist in the different approaches provided by Spring Framework’s JDBC support. This section covers how to address them.spring-doc.cn

Providing SQL Type Information for Parameters

Usually, Spring determines the SQL type of the parameters based on the type of parameter passed in. It is possible to explicitly provide the SQL type to be used when setting parameter values. This is sometimes necessary to correctly set NULL values.spring-doc.cn

You can provide SQL type information in several ways:spring-doc.cn

Many update and query methods of the JdbcTemplate take an additional parameter in the form of an int array. This array is used to indicate the SQL type of the corresponding parameter by using constant values from the java.sql.Types class. Provide one entry for each parameter.spring-doc.cn
You can use the SqlParameterValue class to wrap the parameter value that needs this additional information. To do so, create a new instance for each value and pass in the SQL type and the parameter value in the constructor. You can also provide an optional scale parameter for numeric values.spring-doc.cn
For methods that work with named parameters, you can use the SqlParameterSource classes, BeanPropertySqlParameterSource or MapSqlParameterSource. They both have methods for registering the SQL type for any of the named parameter values.spring-doc.cn

Handling BLOB and CLOB objects

You can store images, other binary data, and large chunks of text in the database. These large objects are called BLOBs (Binary Large OBject) for binary data and CLOBs (Character Large OBject) for character data. In Spring, you can handle these large objects by using the JdbcTemplate directly and also when using the higher abstractions provided by RDBMS Objects and the SimpleJdbc classes. All of these approaches use an implementation of the LobHandler interface for the actual management of the LOB (Large OBject) data. LobHandler provides access to a LobCreator class, through the getLobCreator method, that is used for creating new LOB objects to be inserted.spring-doc.cn

LobCreator and LobHandler provide the following support for LOB input and output:spring-doc.cn

BLOBspring-doc.cn
- byte[]: getBlobAsBytes and setBlobAsBytesspring-doc.cn
- InputStream: getBlobAsBinaryStream and setBlobAsBinaryStreamspring-doc.cn
CLOBspring-doc.cn
- String: getClobAsString and setClobAsStringspring-doc.cn
- InputStream: getClobAsAsciiStream and setClobAsAsciiStreamspring-doc.cn
- Reader: getClobAsCharacterStream and setClobAsCharacterStreamspring-doc.cn

The next example shows how to create and insert a BLOB. Later we show how to read it back from the database.spring-doc.cn

This example uses a JdbcTemplate and an implementation of the AbstractLobCreatingPreparedStatementCallback. It implements one method, setValues. This method provides a LobCreator that we use to set the values for the LOB columns in your SQL insert statement.spring-doc.cn

For this example, we assume that there is a variable, lobHandler, that is already set to an instance of a DefaultLobHandler. You typically set this value through dependency injection.spring-doc.cn

The following example shows how to create and insert a BLOB:spring-doc.cn

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final File blobIn = new File("spring2004.jpg");
final InputStream blobIs = new FileInputStream(blobIn);
final File clobIn = new File("large.txt");
final InputStream clobIs = new FileInputStream(clobIn);
final InputStreamReader clobReader = new InputStreamReader(clobIs);

jdbcTemplate.execute(
	"INSERT INTO lob_table (id, a_clob, a_blob) VALUES (?, ?, ?)",
	new AbstractLobCreatingPreparedStatementCallback(lobHandler) {  (1)
		protected void setValues(PreparedStatement ps, LobCreator lobCreator) throws SQLException {
			ps.setLong(1, 1L);
			lobCreator.setClobAsCharacterStream(ps, 2, clobReader, (int)clobIn.length());  (2)
			lobCreator.setBlobAsBinaryStream(ps, 3, blobIs, (int)blobIn.length());  (3)
		}
	}
);

blobIs.close();
clobReader.close();

1	Pass in the `lobHandler` that (in this example) is a plain `DefaultLobHandler`.
2	Using the method `setClobAsCharacterStream` to pass in the contents of the CLOB.
3	Using the method `setBlobAsBinaryStream` to pass in the contents of the BLOB.

val blobIn = File("spring2004.jpg")
val blobIs = FileInputStream(blobIn)
val clobIn = File("large.txt")
val clobIs = FileInputStream(clobIn)
val clobReader = InputStreamReader(clobIs)

jdbcTemplate.execute(
		"INSERT INTO lob_table (id, a_clob, a_blob) VALUES (?, ?, ?)",
		object: AbstractLobCreatingPreparedStatementCallback(lobHandler) {  (1)
			override fun setValues(ps: PreparedStatement, lobCreator: LobCreator) {
				ps.setLong(1, 1L)
				lobCreator.setClobAsCharacterStream(ps, 2, clobReader, clobIn.length().toInt())  (2)
				lobCreator.setBlobAsBinaryStream(ps, 3, blobIs, blobIn.length().toInt())  (3)
			}
		}
)
blobIs.close()
clobReader.close()

1	Pass in the `lobHandler` that (in this example) is a plain `DefaultLobHandler`.
2	Using the method `setClobAsCharacterStream` to pass in the contents of the CLOB.
3	Using the method `setBlobAsBinaryStream` to pass in the contents of the BLOB.

If you invoke the setBlobAsBinaryStream, setClobAsAsciiStream, or setClobAsCharacterStream method on the LobCreator returned from DefaultLobHandler.getLobCreator(), you can optionally specify a negative value for the contentLength argument. If the specified content length is negative, the DefaultLobHandler uses the JDBC 4.0 variants of the set-stream methods without a length parameter. Otherwise, it passes the specified length on to the driver.spring-doc.cn

See the documentation for the JDBC driver you use to verify that it supports streaming a LOB without providing the content length.spring-doc.cn

Now it is time to read the LOB data from the database. Again, you use a JdbcTemplate with the same instance variable lobHandler and a reference to a DefaultLobHandler. The following example shows how to do so:spring-doc.cn

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List<Map<String, Object>> l = jdbcTemplate.query("select id, a_clob, a_blob from lob_table",
	new RowMapper<Map<String, Object>>() {
		public Map<String, Object> mapRow(ResultSet rs, int i) throws SQLException {
			Map<String, Object> results = new HashMap<String, Object>();
			String clobText = lobHandler.getClobAsString(rs, "a_clob");  (1)
			results.put("CLOB", clobText);
			byte[] blobBytes = lobHandler.getBlobAsBytes(rs, "a_blob");  (2)
			results.put("BLOB", blobBytes);
			return results;
		}
	});

1	Using the method `getClobAsString` to retrieve the contents of the CLOB.
2	Using the method `getBlobAsBytes` to retrieve the contents of the BLOB.

val l = jdbcTemplate.query("select id, a_clob, a_blob from lob_table") { rs, _ ->
	val clobText = lobHandler.getClobAsString(rs, "a_clob")  (1)
	val blobBytes = lobHandler.getBlobAsBytes(rs, "a_blob")  (2)
	mapOf("CLOB" to clobText, "BLOB" to blobBytes)
}

1	Using the method `getClobAsString` to retrieve the contents of the CLOB.
2	Using the method `getBlobAsBytes` to retrieve the contents of the BLOB.

1	Pass in the `lobHandler` that (in this example) is a plain `DefaultLobHandler`.
2	Using the method `setClobAsCharacterStream` to pass in the contents of the CLOB.
3	Using the method `setBlobAsBinaryStream` to pass in the contents of the BLOB.

1	Pass in the `lobHandler` that (in this example) is a plain `DefaultLobHandler`.
2	Using the method `setClobAsCharacterStream` to pass in the contents of the CLOB.
3	Using the method `setBlobAsBinaryStream` to pass in the contents of the BLOB.

See the documentation for the JDBC driver you use to verify that it supports streaming a LOB without providing the content length.spring-doc.cn

1	Using the method `getClobAsString` to retrieve the contents of the CLOB.
2	Using the method `getBlobAsBytes` to retrieve the contents of the BLOB.

1	Using the method `getClobAsString` to retrieve the contents of the CLOB.
2	Using the method `getBlobAsBytes` to retrieve the contents of the BLOB.

Passing in Lists of Values for IN Clause

The SQL standard allows for selecting rows based on an expression that includes a variable list of values. A typical example would be select * from T_ACTOR where id in (1, 2, 3). This variable list is not directly supported for prepared statements by the JDBC standard. You cannot declare a variable number of placeholders. You need a number of variations with the desired number of placeholders prepared, or you need to generate the SQL string dynamically once you know how many placeholders are required. The named parameter support provided in the NamedParameterJdbcTemplate takes the latter approach. You can pass in the values as a java.util.List (or any Iterable) of simple values. This list is used to insert the required placeholders into the actual SQL statement and pass in the values during statement execution.spring-doc.cn

Be careful when passing in many values. The JDBC standard does not guarantee that you can use more than 100 values for an IN expression list. Various databases exceed this number, but they usually have a hard limit for how many values are allowed. For example, Oracle’s limit is 1000.

In addition to the primitive values in the value list, you can create a java.util.List of object arrays. This list can support multiple expressions being defined for the in clause, such as select * from T_ACTOR where (id, last_name) in ((1, 'Johnson'), (2, 'Harrop')). This, of course, requires that your database supports this syntax.spring-doc.cn

Handling Complex Types for Stored Procedure Calls

When you call stored procedures, you can sometimes use complex types specific to the database. To accommodate these types, Spring provides a SqlReturnType for handling them when they are returned from the stored procedure call and SqlTypeValue when they are passed in as a parameter to the stored procedure.spring-doc.cn

The SqlReturnType interface has a single method (named getTypeValue) that must be implemented. This interface is used as part of the declaration of an SqlOutParameter. The following example shows returning the value of a java.sql.Struct object of the user declared type ITEM_TYPE:spring-doc.cn

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import java.sql.CallableStatement;
import java.sql.Struct;
import java.sql.Types;

import javax.sql.DataSource;

import org.springframework.jdbc.core.SqlOutParameter;
import org.springframework.jdbc.object.StoredProcedure;

public class TestItemStoredProcedure extends StoredProcedure {

	public TestItemStoredProcedure(DataSource dataSource) {
		super(dataSource, "get_item");
		declareParameter(new SqlOutParameter("item", Types.STRUCT, "ITEM_TYPE",
				(CallableStatement cs, int colIndx, int sqlType, String typeName) -> {
					Struct struct = (Struct) cs.getObject(colIndx);
					Object[] attr = struct.getAttributes();
					TestItem item = new TestItem();
					item.setId(((Number) attr[0]).longValue());
					item.setDescription((String) attr[1]);
					item.setExpirationDate((java.util.Date) attr[2]);
					return item;
				}));
		// ...
	}

}

import org.springframework.jdbc.core.SqlOutParameter
import org.springframework.jdbc.`object`.StoredProcedure
import java.sql.CallableStatement
import java.sql.Struct
import java.sql.Types
import java.util.Date
import javax.sql.DataSource

class TestItemStoredProcedure(dataSource: DataSource) : StoredProcedure(dataSource, "get_item") {
	init {
		declareParameter(SqlOutParameter("item",Types.STRUCT,"ITEM_TYPE") {
				cs: CallableStatement, colIndx: Int, _: Int, _: String? ->
				val struct = cs.getObject(colIndx) as Struct
				val attr = struct.attributes
				val item = TestItem()
				item.id = (attr[0] as Number).toLong()
				item.description = attr[1] as String
				item.expirationDate = attr[2] as Date
				item
			})
		// ...
	}
}

You can use SqlTypeValue to pass the value of a Java object (such as TestItem) to a stored procedure. The SqlTypeValue interface has a single method (named createTypeValue) that you must implement. The active connection is passed in, and you can use it to create database-specific objects, such as java.sql.Struct instances or java.sql.Array instances. The following example creates a java.sql.Struct instance:spring-doc.cn

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TestItem testItem = new TestItem(123L, "A test item",
		new SimpleDateFormat("yyyy-M-d").parse("2010-12-31"));

SqlTypeValue value = new AbstractSqlTypeValue() {
	protected Object createTypeValue(Connection connection, int sqlType, String typeName) throws SQLException {
		Object[] item = new Object[] { testItem.getId(), testItem.getDescription(),
				new java.sql.Date(testItem.getExpirationDate().getTime()) };
		return connection.createStruct(typeName, item);
	}
};

val testItem = TestItem(123L, "A test item",
	SimpleDateFormat("yyyy-M-d").parse("2010-12-31"))

val value = object : AbstractSqlTypeValue() {
	override fun createTypeValue(connection: Connection, sqlType: Int, typeName: String?): Any {
		val item = arrayOf<Any>(testItem.id, testItem.description,
			Date(testItem.expirationDate.time))
		return connection.createStruct(typeName, item)
	}
}

You can now add this SqlTypeValue to the Map that contains the input parameters for the execute call of the stored procedure.spring-doc.cn

Another use for the SqlTypeValue is passing in an array of values to an Oracle stored procedure. Oracle has an createOracleArray method on OracleConnection that you can access by unwrapping it. You can use the SqlTypeValue to create an array and populate it with values from the Java java.sql.Array, as the following example shows:spring-doc.cn

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Long[] ids = new Long[] {1L, 2L};

SqlTypeValue value = new AbstractSqlTypeValue() {
	protected Object createTypeValue(Connection conn, int sqlType, String typeName) throws SQLException {
		return conn.unwrap(OracleConnection.class).createOracleArray(typeName, ids);
	}
};

val ids = arrayOf(1L, 2L)
val value: SqlTypeValue = object : AbstractSqlTypeValue() {
	override fun createTypeValue(conn: Connection, sqlType: Int, typeName: String?): Any {
		return conn.unwrap(OracleConnection::class.java).createOracleArray(typeName, ids)
	}
}