Oracle9i JDBC Developer's Guide and Reference Release 1 (9.0.1) Part Number A90211-01 |
|
This chapter describes how you use JDBC and the oracle.sql.*
classes to access and manipulate LOB and BFILE locators and data, covering the following topics:
LOBs ("large objects") are stored in a way that optimizes space and provides efficient access. The JDBC drivers provide support for two types of LOBs: BLOBs (unstructured binary data) and CLOBs (character data). BLOB and CLOB data is accessed and referenced by using a locator, which is stored in the database table and points to the BLOB or CLOB data, which is outside the table.
BFILEs are large binary data objects stored in operating system files outside of database tablespaces. These files use reference semantics. They can also be located on tertiary storage devices such as hard disks, CD-ROMs, PhotoCDs and DVDs. As with BLOBs and CLOBs, a BFILE is accessed and referenced by a locator which is stored in the database table and points to the BFILE data.
To work with LOB data, you must first obtain a LOB locator. Then you can read or write LOB data and perform data manipulation. The following sections also describe how to create and populate a LOB column in a table.
The JDBC drivers support these oracle.sql.*
classes for BLOBs, CLOBs, and BFILEs:
The oracle.sql.BLOB
and CLOB
classes implement the java.sql.Blob
and Clob
interfaces, respectively (oracle.jdbc2.Blob
and Clob
interfaces under JDK 1.1.x). By contrast, BFILE
is an Oracle extension, without a corresponding java.sql
(or oracle.jdbc2
) interface.
Instances of these classes contain only the locators for these datatypes, not the data. After accessing the locators, you must perform some additional steps to access the data. These steps are described in "Reading and Writing BLOB and CLOB Data" and "Reading BFILE Data".
This section describes how to read and write data to and from binary large objects (BLOBs) and character large objects (CLOBs) in an Oracle database, using LOB locators.
For general information about Oracle9i LOBs and how to use them, see the Oracle9i Application Developer's Guide - Large Objects (LOBs).
Standard as well as Oracle-specific getter and setter methods are available for retrieving or passing LOB locators from or to the database.
Given a standard JDBC result set (java.sql.ResultSet
) or callable statement (java.sql.CallableStatement
) that includes BLOB or CLOB locators, you can access the locators by using standard getter methods, as follows. All the standard and Oracle-specific getter methods discussed here take either an int
column index or a String
column name as input.
getBlob()
and getClob()
methods, which return java.sql.Blob
and Clob
objects, respectively.
getObject()
method, which returns java.lang.Object
, and cast the output as desired.
If you retrieve or cast the result set or callable statement to an OracleResultSet
or OracleCallableStatement
object, then you can use Oracle extensions as follows:
getBLOB()
and getCLOB()
, which return oracle.sql.BLOB
and CLOB
objects, respectively.
getOracleObject()
method, which returns an oracle.sql.Datum
object, and cast the output appropriately.
getBlob()
and getClob()
, which return oracle.jdbc2.Blob
and Clob
objects, respectively. (These Blob
and Clob
interfaces mimic the standard interfaces available in JDK 1.2.x.)
If using
Note:
getObject()
or getOracleObject()
, then remember to cast the output, as necessary. For more information, see "Casting Your get Method Return Values".
Assume the database has a table called lob_table
with a column for a BLOB locator, blob_col
, and a column for a CLOB locator, clob_col
. This example assumes that you have already created the Statement
object, stmt
.
First, select the LOB locators into a standard result set, then get the LOB data into appropriate Java classes:
// Select LOB locator into standard result set. ResultSet rs = stmt.executeQuery ("SELECT blob_col, clob_col FROM lob_table"); while (rs.next()) { // Get LOB locators into Java wrapper classes. java.sql.Blob blob = (java.sql.Blob)rs.getObject(1); java.sql.Clob clob = (java.sql.Clob)rs.getObject(2); (...process...) }
The output is cast to java.sql.Blob
and Clob
. As an alternative, you can cast the output to oracle.sql.BLOB
and CLOB
to take advantage of extended functionality offered by the oracle.sql.*
classes. For example, you can rewrite the above code to get the LOB locators as:
// Get LOB locators into Java wrapper classes. oracle.sql.BLOB blob = (BLOB)rs.getObject(1); oracle.sql.CLOB clob = (CLOB)rs.getObject(2); (...process...)
The callable statement methods for retrieving LOBs are identical to the result set methods.
For example, if you have an OracleCallableStatement
ocs
that calls a function func
that has a CLOB output parameter, then set up the callable statement as in the following example.
This example registers OracleTypes.CLOB
as the typecode of the output parameter.
OracleCallableStatement ocs = (OracleCallableStatement)conn.prepareCall("{? = call func()}"); ocs.registerOutParameter(1, OracleTypes.CLOB); ocs.execute(); oracle.sql.CLOB clob = ocs.getCLOB(1);
Given a standard JDBC prepared statement (java.sql.PreparedStatement
) or callable statement (java.sql.CallableStatement
), you can use standard setter methods to pass LOB locators, as follows. All the standard and Oracle-specific setter methods discussed here take an int
parameter index and the LOB locator as input.
setBlob()
and setClob()
methods, which take java.sql.Blob
and Clob
locators as input.
setObject()
method, which simply specifies a java.lang.Object
input.
Given an Oracle-specific OraclePreparedStatement
or OracleCallableStatement
, then you can use Oracle extensions as follows:
setBLOB()
and setCLOB()
, which take oracle.sql.BLOB
and CLOB
locators as input, respectively.
setOracleObject()
method, which simply specifies an oracle.sql.Datum
input.
setBlob()
and setClob()
, which take oracle.jdbc2.Blob
and Clob
locators as input, respectively. (These Blob
and Clob
interfaces mimic the standard interfaces available in JDK 1.2.x.)
If you have an OraclePreparedStatement
object ops
and a BLOB named my_blob
, then write the BLOB to the database as follows:
OraclePreparedStatement ops = (OraclePreparedStatement)conn.prepareStatement ("INSERT INTO blob_table VALUES(?)"); ops.setBLOB(1, my_blob); ops.execute();
If you have an OracleCallableStatement
object ocs
and a CLOB named my_clob
, then input the CLOB to the stored procedure proc
as follows:
OracleCallableStatement ocs = (OracleCallableStatement)conn.prepareCall("{call proc(?))}"); ocs.setClob(1, my_clob); ocs.execute();
Once you have a LOB locator, you can use JDBC methods to read and write the LOB data. LOB data is materialized as a Java array or stream. However, unlike most Java streams, a locator representing the LOB data is stored in the table. Thus, you can access the LOB data at any time during the life of the connection.
To read and write the LOB data, use the methods in the oracle.sql.BLOB
or oracle.sql.CLOB
class, as appropriate. These classes provide functionality such as reading from the LOB into an input stream, writing from an output stream into a LOB, determining the length of a LOB, and closing a LOB.
To read and write LOB data, you can use these methods:
getBinaryStream()
method of an oracle.sql.BLOB
object to retrieve the entire BLOB
as an input stream. This returns a java.io.InputStream
object.
As with any InputStream
object, use one of the overloaded read()
methods to read the LOB data, and use the close()
method when you finish.
getBinaryOutputStream()
method of an oracle.sql.BLOB
object to retrieve the BLOB as an output stream. This returns a java.io.OutputStream
object to be written back to the BLOB.
As with any OutputStream
object, use one of the overloaded write()
methods to update the LOB data, and use the close()
method when you finish.
getAsciiStream()
or getCharacterStream()
method of an oracle.sql.CLOB
object to retrieve the entire CLOB as an input stream. The getAsciiStream()
method returns an ASCII input stream in a java.io.InputStream
object. The getCharacterStream()
method returns a Unicode
input stream in a java.io.Reader
object.
As with any InputStream
or Reader
object, use one of the overloaded read()
methods to read the LOB data, and use the close()
method when you finish.
You can also use the getSubString()
method of oracle.sql.CLOB
object to retrieve a subset of the CLOB as a character string of type java.lang.String
.
getAsciiOutputStream()
or getCharacterOutputStream()
method of an oracle.sql.CLOB
object to retrieve the CLOB as an output stream to be written back to the CLOB. The getAsciiOutputStream()
method returns an ASCII output stream in a java.io.OutputStream
object. The getCharacterOutputStream()
method returns a Unicode
output stream in a java.io.Writer
object.
As with any OutputStream
or Writer
object, use one of the overloaded write()
methods to update the LOB data, and use the flush()
and close()
methods when you finish.
Use the getBinaryStream()
method of the oracle.sql.BLOB
class to read BLOB data. The getBinaryStream()
method reads the BLOB data into a binary stream.
The following example uses the getBinaryStream()
method to read BLOB data into a byte stream and then reads the byte stream into a byte array (returning the number of bytes read, as well).
// Read BLOB data from BLOB locator. InputStream byte_stream = my_blob.getBinaryStream(); byte [] byte_array = new byte [10]; int bytes_read = byte_stream.read(byte_array); ...
The following example uses the getCharacterStream()
method to read CLOB
data into a Unicode
character stream. It then reads the character stream into a character array (returning the number of characters read, as well).
// Read CLOB data from CLOB locator into Reader char stream. Reader char_stream = my_clob.getCharacterStream(); char [] char_array = new char [10]; int chars_read = char_stream.read (char_array, 0, 10); ...
The next example uses the getAsciiStream()
method of the oracle.sql.CLOB
class to read CLOB data into an ASCII character stream. It then reads the ASCII stream into a byte array (returning the number of bytes read, as well).
// Read CLOB data from CLOB locator into Input ASCII character stream Inputstream asciiChar_stream = my_clob.getAsciiStream(); byte[] asciiChar_array = new byte[10]; int asciiChar_read = asciiChar_stream.read(asciiChar_array,0,10);
Use the getBinaryOutputStream()
method of an oracle.sql.BLOB
object to write BLOB data.
The following example reads a vector of data into a byte array, then uses the getBinaryOutputStream()
method to write an array of character data to a BLOB.
java.io.OutputStream outstream; // read data into a byte array byte[] data = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}; // write the array of binary data to a BLOB outstream = ((BLOB)my_blob).getBinaryOutputStream(); outstream.write(data); ...
Use the getCharacterOutputStream()
method or the getAsciiOutputStream()
method to write data to a CLOB. The getCharacterOutputStream()
method returns a Unicode
output stream; the getAsciiOutputStream()
method returns an ASCII output stream.
The following example reads a vector of data into a character array, then uses the getCharacterOutputStream()
method to write the array of character data to a CLOB. The getCharacterOutputStream()
method returns a java.io.Writer
instance in an oracle.sql.CLOB
object, not a java.sql.Clob
object.
java.io.Writer writer; // read data into a character array char[] data = {'0','1','2','3','4','5','6','7','8','9'}; // write the array of character data to a CLOB writer = ((CLOB)my_clob).getCharacterOutputStream(); writer.write(data); writer.flush(); writer.close(); ...
The next example reads a vector of data into a byte array, then uses the getAsciiOutputStream()
method to write the array of ASCII data to a CLOB. Because getAsciiOutputStream()
returns an ASCII output stream, you must cast the output to a oracle.sql.CLOB
datatype.
java.io.OutputStream out; // read data into a byte array byte[] data = {'0','1','2','3','4','5','6','7','8','9'}; // write the array of ascii data to a CLOB out = ((CLOB)clob).getAsciiOutputStream(); out.write(data); out.flush(); out.close();
Create and populate a BLOB
or CLOB
column in a table by using SQL statements.
Create a BLOB
or CLOB
column in a table with the SQL CREATE TABLE
statement, then populate the LOB. This includes creating the LOB entry in the table, obtaining the LOB locator, creating a file handler for the data (if you are reading the data from a file), and then copying the data into the LOB.
To create a BLOB
or CLOB
column in a new table, execute the SQL CREATE TABLE
statement. The following example code creates a BLOB
column in a new table. This example assumes that you have already created your Connection
object conn
and Statement
object stmt
:
String cmd = "CREATE TABLE my_blob_table (x varchar2 (30), c blob)"; stmt.execute (cmd);
In this example, the VARCHAR2
column designates a row number, such as 1 or 2, and the BLOB
column stores the locator of the BLOB data.
This example demonstrates how to populate a BLOB
or CLOB
column by reading data from a stream. These steps assume that you have already created your Connection
object conn
and Statement
object stmt
. The table my_blob_table
is the table that was created in the previous section.
The following example writes the GIF
file john.gif
to a BLOB.
empty_blob
syntax to create the BLOB locator.
stmt.execute ("INSERT INTO my_blob_table VALUES ('row1', empty_blob())");
BLOB blob; cmd = "SELECT * FROM my_blob_table WHERE X='row1'"; ResultSet rest = stmt.executeQuery(cmd); BLOB blob = ((OracleResultSet)rset).getBLOB(2);
john.gif
file, then print the length of the file. This value will be used later to ensure that the entire file is read into the BLOB. Next, create a FileInputStream
object to read the contents of the GIF
file, and an OutputStream
object to retrieve the BLOB as a stream.
File binaryFile = new File("john.gif"); System.out.println("john.gif length = " + binaryFile.length()); FileInputStream instream = new FileInputStream(binaryFile); OutputStream outstream = blob.getBinaryOutputStream();
getBufferSize()
to retrieve the ideal buffer size (according to calculations by the JDBC driver) to use in writing to the BLOB, then create the buffer
byte array.
int size = blob.getBufferSize(); byte[] buffer = new byte[size]; int length = -1;
read()
method to read the GIF
file to the byte array buffer
, then use the write()
method to write it to the BLOB. When you finish, close the input and output streams.
while ((length = instream.read(buffer)) != -1) outstream.write(buffer, 0, length); instream.close(); outstream.close();
Once your data is in the BLOB or CLOB, you can manipulate the data. This is described in the next section, "Accessing and Manipulating BLOB and CLOB Data".
Once you have your BLOB or CLOB locator in a table, you can access and manipulate the data to which it points. To access and manipulate the data, you first must select their locators from a result set or from a callable statement. "Getting and Passing BLOB and CLOB Locators" describes these techniques in detail.
After you select the locators, you can retrieve the BLOB or CLOB data. You will usually want to cast the result set to the OracleResultSet
datatype so that you can retrieve the data in oracle.sql.*
format. After retrieving the BLOB or CLOB data, you can manipulate it however you want.
This example is a continuation of the example in the previous section. It uses the SQL SELECT
statement to select the BLOB locator from the table my_blob_table
into a result set. The result of the data manipulation is to print the length of the BLOB in bytes.
// Select the blob - what we are really doing here // is getting the blob locator into a result set BLOB blob; cmd = "SELECT * FROM my_blob_table"; ResultSet rset = stmt.executeQuery (cmd); // Get the blob data - cast to OracleResult set to // retrieve the data in oracle.sql format String index = ((OracleResultSet)rset).getString(1); blob = ((OracleResultSet)rset).getBLOB(2); // get the length of the blob int length = blob.length(); // print the length of the blob System.out.println("blob length" + length); // read the blob into a byte array // then print the blob from the array byte bytes[] = blob.getBytes(1, length); printBytes(bytes, length);
In addition to what has already been discussed in this chapter, the oracle.sql.BLOB
and CLOB
classes have a number of methods for further functionality.
The oracle.sql.BLOB
class includes the following methods:
close():
Closes the BLOB associated with the locator. (See "Using Open and Close With LOBs" for more information.)
freeTemporary()
: Frees the storage used by a temporary BLOB. (See "Working With Temporary LOBs" for more information.)
getBinaryOutputStream()
: Returns a java.io.OutputStream
to write data to the BLOB as a stream.
getBinaryOutputStream(long)
: Returns a java.io.OutputStream
to write data to the BLOB as a stream. The data is written beginning at the position in the BLOB specified in the argument.
getBinaryStream()
: Returns the BLOB data for this Blob
instance as a stream of bytes.
getBinaryStream(long)
: Returns the BLOB data for this Blob instance as a stream of bytes beginning at the position in the BLOB specified in the argument.
getBufferSize()
: Returns the ideal buffer size, according to calculations by the JDBC driver, to use in reading and writing BLOB data. This value is a multiple of the chunk size (see getChunkSize()
below) and is close to 32K.
getBytes()
: Reads from the BLOB data, starting at a specified point, into a supplied buffer.
getChunkSize()
: Returns the Oracle chunking size, which can be specified by the database administrator when the LOB column is first created. This value, in Oracle blocks, determines the size of the chunks of data read or written by the LOB data layer in accessing or modifying the BLOB value. Part of each chunk stores system-related information, and the rest stores LOB data. Performance is enhanced if read and write requests use some multiple of the chunk size.
isOpen()
: Returns true
if the BLOB was opened by calling the open()
method; otherwise, it returns false
. (See "Using Open and Close With LOBs" for more information.)
isTemporary()
: Returns true if the BLOB is a temporary BLOB. (See "Working With Temporary LOBs" for more information.)
length()
: Returns the length of the BLOB in bytes.
open()
: Opens the BLOB associated with the locator. (See "Using Open and Close With LOBs" for more information.)
open(int)
: Opens the BLOB associated with the locator in the mode specified by the argument. (See "Using Open and Close With LOBs" for more information.)
position()
: Determines the byte position in the BLOB where a given pattern begins.
putBytes()
: Writes BLOB data, starting at a specified point, from a supplied buffer.
trim(long)
: Trims the value of the BLOB to the length specified by the argument.
The oracle.sql.CLOB
class includes the following methods:
close()
: Closes the CLOB associated with the locator. (See "Using Open and Close With LOBs" for more information.)
freeTemporary()
: Frees the storage used by a temporary CLOB. (See "Working With Temporary LOBs" for more information.)
getAsciiOutputStream()
: Returns a java.io.OutputStream
to write data to the CLOB as a stream.
getAsciiOutputStream(long)
: Returns a java.io.OutputStream
object to write data to the CLOB as a stream. The data is written beginning at the position in the CLOB specified by the argument.
getAsciiStream()
: Returns the CLOB value designated by the Clob
object as a stream of ASCII bytes.
getAsciiStream(long)
: Returns the CLOB value designated by the CLOB object as a stream of ASCII bytes, beginning at the position in the CLOB specified by the argument.
getBufferSize()
: Returns the ideal buffer size, according to calculations by the JDBC driver, to use in reading and writing CLOB data. This value is a multiple of the chunk size (see getChunkSize()
below) and is close to 32K.
getCharacterOutputStream()
: Returns a java.io.Writer
to write data to the CLOB as a stream.
getCharacterOutputStream(long)
: Returns a java.io.Writer
object to write data to the CLOB as a stream. The data is written beginning at the position in the CLOB specified by the argument.
getCharacterStream()
: Returns the CLOB data as a stream of Unicode
characters.
getCharacterStream(long)
: Returns the CLOB data as a stream of Unicode characters beginning at the position in the CLOB specified by the argument.
getChars()
: Retrieves characters from a specified point in the CLOB data into a character array.
getChunkSize()
: Returns the Oracle chunking size, which can be specified by the database administrator when the LOB column is first created. This value, in Oracle blocks, determines the size of the chunks of data read or written by the LOB data layer in accessing or modifying the CLOB value. Part of each chunk stores system-related information and the rest stores LOB data. Performance is enhanced if you make read and write requests using some multiple of the chunk size.
isOpen()
: Returns true
if the CLOB was opened by calling the open() method; otherwise, it returns false
. (See "Using Open and Close With LOBs" for more information.)
isTemporary()
: Returns true if and only if the CLOB is a temporary CLOB. (See "Working With Temporary LOBs" for more information.)
length()
: Returns the length of the CLOB in characters.
open()
: Opens the CLOB associated with the locator. (See "Using Open and Close With LOBs" for more information.)
open(int)
: Opens the CLOB associated with the locator in the mode specified by the argument. (See "Using Open and Close With LOBs" for more information.)
position()
: Determines the character position in the CLOB at which a given substring begins.
putChars()
: Writes characters from a character array to a specified point in the CLOB data.
getSubString()
: Retrieves a substring from a specified point in the CLOB data.
putString()
: Writes a string to a specified point in the CLOB data.
trim(long)
: Trims the value of the CLOB to the length specified by the argument.
Before writing data to an internal LOB, you must make sure the LOB column/attribute is not null
: it must contain a locator. You can accomplish this by initializing the internal LOB as an empty LOB in an INSERT
or UPDATE
statement, using the empty_lob()
method defined in the oracle.sql.BLOB
and oracle.sql.CLOB
classes:
public static BLOB empty_lob() throws SQLException
public static CLOB empty_lob() throws SQLException
A JDBC driver creates an empty LOB
instance without making database round trips. You can use empty LOBs in the following:
setXXX()
methods of the OraclePreparedStatement
class
updateXXX()
methods of updatable result sets
STRUCT
objects
ARRAY
objects
You can use temporary LOBs to store transient data. The data is stored in temporary table space rather than regular table space. You should free temporary LOBs after you no longer need them. If you do not, the space the LOB consumes in temporary table space will not be reclaimed.
You create a temporary LOB with the static method, createTemporary(Connection, boolean, int)
, defined in the oracle.sql.BLOB
and oracle.sql.CLOB
classes. You free a temporary LOB with the freeTemporary()
method.
public static BLOB createTemporary(Connection conn, boolean isCached, int duration); public static CLOB createTemporary(Connection conn, boolean isCached, int duration);
The duration must be either DURATION_SESSION
or DURATION_CALL
as defined in the oracle.sql.BLOB
or oracle.sql.CLOB
class. In client applications DURATION_SESSION
is appropriate. In Java stored procedures you can use either DURATION_SESSION
or DURATION_CALL
, which ever is appropriate.
You can test whether a LOB is temporary by calling the isTemporary()
method. If the LOB was created by calling the createTemporary()
method, the isTemporary()
method returns true
; otherwise, it returns false
.
You can free a temporary LOB by calling the freeTemporary()
method. Free any temporary LOBs before ending the session or call. Otherwise, the storage used by the temporary LOB will not be reclaimed.
You do not have to open and close your LOBs. You might choose to open and close them for performance reasons.
If you do not wrap LOB operations inside an Open/Close call operation: Each modification to the LOB will implicitly open and close the LOB thereby firing any triggers on an domain index. Note that in this case, any domain indexes on the LOB will become updated as soon as LOB modifications are made. Therefore, domain LOB indexes are always valid and may be used at any time.
If you wrap your LOB operations inside the Open/Close operation, triggers will not be fired for each LOB modification. Instead, the trigger on domain indexes will be fired at the Close call. For example, you might design your application so that domain indexes are not be updated until you call the close()
method. However, this means that any domain indexes on the LOB will not be valid in-between the Open/Close calls.
You open a LOB by calling the open()
or open(int)
method. You may then read and write the LOB without any triggers associated with that LOB firing. When you are done accessing the LOB, close the LOB by calling the close()
method. When you close the LOB, any triggers associated with the LOB will fire. You can see if a LOB is open or closed by calling the isOpen()
method. If you open the LOB by calling the open(int)
method, the value of the argument must be either MODE_READONLY
or MODE_READWRITE
, as defined in the oracle.sql.BLOB
and oracle.sql.CLOB
classes. If you open the LOB with MODE_READONLY
, any attempt to write to the LOB will result in a SQL exception.
This section describes how to read and write data to and from external binary files (BFILEs), using file locators.
Getter and setter methods are available for retrieving or passing BFILE locators from or to the database.
Given a standard JDBC result set or callable statement object that includes BFILE locators, you can access the locators by using the standard result set getObject()
method. This method returns an oracle.sql.BFILE
object.
You can also access the locators by casting your result set to OracleResultSet
or your callable statement to OracleCallableStatement
and using the getOracleObject()
or getBFILE()
method.
Notes:
|
Assume that the database has a table called bfile_table
with a single column for the BFILE locator bfile_col
. This example assumes that you have already created your Statement
object stmt
.
Select the BFILE locator into a standard result set. If you cast the result set to an OracleResultSet
, you can use getBFILE()
to get the BFILE locator:
// Select the BFILE locator into a result set ResultSet rs = stmt.executeQuery("SELECT bfile_col FROM bfile_table"); while (rs.next()) { oracle.sql.BFILE my_bfile = ((OracleResultSet)rs).getBFILE(1); }
Note that as an alternative, you can use getObject()
to return the BFILE locator. In this case, because getObject()
returns a java.lang.Object
, cast the results to BFILE
. For example:
oracle.sql.BFILE my_bfile = (BFILE)rs.getObject(1);
Assume you have an OracleCallableStatement
object ocs
that calls a function func
that has a BFILE
output parameter. The following code example sets up the callable statement, registers the output parameter as OracleTypes.BFILE
, executes the statement, and retrieves the BFILE locator:
OracleCallableStatement ocs = (OracleCallableStatement)conn.prepareCall("{? = call func()}"); ocs.registerOutParameter(1, OracleTypes.BFILE); ocs.execute(); oracle.sql.BFILE bfile = ocs.getBFILE(1);
To pass a BFILE locator to a prepared statement or callable statement (to update a BFILE locator, for example), you can do one of the following:
or:
OraclePreparedStatement
or OracleCallableStatement
, and use the setOracleObject()
or setBFILE()
method.
These methods take the parameter index and an oracle.sql.BFILE
object as input.
Assume you want to insert a BFILE locator into a table, and you have an OraclePreparedStatement
object ops
to insert data into a table. The first column is a string (to designate a row number), the second column is a BFILE, and you have a valid oracle.sql.BFILE
object (bfile
). Write the BFILE to the database as follows:
OraclePreparedStatement ops = (OraclePreparedStatement)conn.prepareStatement ("INSERT INTO my_bfile_table VALUES (?,?)"); ops.setString(1,"one"); ops.setBFILE(2, bfile); ops.execute();
Passing a BFILE locator to a callable statement is similar to passing it to a prepared statement. In this case, the BFILE locator is passed to the myGetFileLength()
procedure, which returns the BFILE length as a numeric value.
OracleCallableStatement cstmt = (OracleCallableStatement)conn.prepareCall ("begin ? := myGetFileLength (?); end;"); try { cstmt.registerOutParameter (1, Types.NUMERIC); cstmt.setBFILE (2, bfile); cstmt.execute (); return cstmt.getLong (1); }
To read BFILE data, you must first get the BFILE locator. You can get the locator from either a callable statement or a result set. "Getting and Passing BFILE Locators" describes this.
Once you obtain the locator, you can invoke a number of methods on the BFILE without opening it. For example, you can use the oracle.sql.BFILE
methods fileExists()
and isFileOpen()
to determine whether the BFILE exists and if it is open. If you want to read and manipulate the data, however, you must open and close the BFILE, as follows:
openFile()
method of the oracle.sql.BFILE
class to open a BFILE.
closeFile()
method of the BFILE
class.
BFILE data is materialized as a Java stream. To read from a BFILE, use the getBinaryStream()
method of an oracle.sql.BFILE
object to retrieve the entire file as an input stream. This returns a java.io.InputStream
object.
As with any InputStream
object, use one of the overloaded read()
methods to read the file data, and use the close()
method when you finish.
The following example uses the getBinaryStream()
method of an oracle.sql.BFILE
object to read BFILE data into a byte stream and then read the byte stream into a byte array. The example assumes that the BFILE has already been opened.
// Read BFILE data from a BFILE locator Inputstream in = bfile.getBinaryStream(); byte[] byte_array = new byte{10}; int byte_read = in.read(byte_array);
This section discusses how to create a BFILE
column in a table with SQL operations and specify the location where the BFILE resides. The examples below assume that you have already created your Connection
object conn
and Statement
object stmt
.
To work with BFILE data, create a BFILE
column in a table, and specify the location of the BFILE. To specify the location of the BFILE, use the SQL CREATE DIRECTORY
...AS
statement to specify an alias for the directory where the BFILE resides. Then execute the statement. In this example, the directory alias is test_dir
, and the BFILE resides in the /home/work
directory.
String cmd; cmd = "CREATE DIRECTORY test_dir AS '/home/work'"; stmt.execute (cmd);
Use the SQL CREATE
TABLE
statement to create a table containing a BFILE
column, then execute the statement. In this example, the name of the table is my_bfile_table
.
// Create a table containing a BFILE field cmd = "CREATE TABLE my_bfile_table (x varchar2 (30), b bfile)"; stmt.execute (cmd);
In this example, the VARCHAR2
column designates a row number, and the BFILE
column stores the locator of the BFILE data.
Use the SQL INSERT INTO...VALUES
statement to populate the VARCHAR2
and BFILE
fields, then execute the statement. The BFILE
column is populated with the locator to the BFILE data. To populate the BFILE
column, use the bfilename
function to specify the directory alias and the name of the BFILE file.
cmd ="INSERT INTO my_bfile_table VALUES ('one', bfilename(test_dir, 'file1.data'))"; stmt.execute (cmd); cmd ="INSERT INTO my_bfile_table VALUES ('two', bfilename(test_dir, 'jdbcTest.data'))"; stmt.execute (cmd);
In this example, the name of the directory alias is test_dir
. The locator of the BFILE file1.data
is loaded into the BFILE
column on row one
, and the locator of the BFILE
jdbcTest.data
is loaded into the bfile
column on row two
.
As an alternative, you might want to create the row for the row number and BFILE locator now, but wait until later to insert the locator. In this case, insert the row number into the table, and null
as a place holder for the BFILE locator.
cmd ="INSERT INTO my_bfile_table VALUES ('three', null)"; stmt.execute(cmd);
Here, three
is inserted into the row number column, and null
is inserted as the place holder. Later in your program, insert the BFILE locator into the table by using a prepared statement.
First get a valid BFILE locator into the bfile
object:
rs = stmt.executeQuery("SELECT b FROM my_bfile_table WHERE x='two'"); rs.next(); oracle.sql.BFILE bfile = ((OracleResultSet)rs).getBFILE(1);
Then, create your prepared statement. Note that because this example uses the setBFILE()
method to identify the BFILE, the prepared statement must be cast to an OraclePreparedStatement
:
OraclePreparedStatement ops = (OraclePreparedStatement)conn.prepareStatement (UPDATE my_bfile_table SET b=? WHERE x = 'three'); ops.setBFILE(1, bfile); ops.execute();
Now row two
and row three
contain the same BFILE.
Once you have the BFILE locators available in a table, you can access and manipulate the BFILE data. The next section, "Accessing and Manipulating BFILE Data", describes this.
Once you have the BFILE locator in a table, you can access and manipulate the data to which it points. To access and manipulate the data, you must first select its locator from a result set or a callable statement.
The following code continues the example from "Populating a BFILE Column", getting the locator of the BFILE from row two
of a table into a result set. The result set is cast to an OracleResultSet
so that oracle.sql.*
methods can be used on it. Several of the methods applied to the BFILE, such as getDirAlias()
and getName()
, do not require you to open the BFILE. Methods that manipulate the BFILE data, such as reading, getting the length, and displaying, do require you to open the BFILE.
When you finish manipulating the BFILE data, you must close the BFILE. For a complete BFILE example, see "BFILEs--FileExample.java".
// select the bfile locator cmd = "SELECT * FROM my_bfile_table WHERE x = 'two'"; rset = stmt.executeQuery (cmd); if (rset.next ()) BFILE bfile = ((OracleResultSet)rset).getBFILE (2); // for these methods, you do not have to open the bfile println("getDirAlias() = " + bfile.getDirAlias()); println("getName() = " + bfile.getName()); println("fileExists() = " + bfile.fileExists()); println("isFileOpen() = " + bfile.isFileOpen()); // now open the bfile to get the data bfile.openFile(); // get the BFILE data as a binary stream InputStream in = bfile.getBinaryStream(); int length ; // read the bfile data in 6-byte chunks byte[] buf = new byte[6]; while ((length = in.read(buf)) != -1) { // append and display the bfile data in 6-byte chunks StringBuffer sb = new StringBuffer(length); for (int i=0; i<length; i++) sb.append( (char)buf[i] ); System.out.println(sb.toString()); } // we are done working with the input stream. Close it. in.close(); // we are done working with the BFILE. Close it. bfile.closeFile();
In addition to the features already discussed in this chapter, the oracle.sql.BFILE
class has a number of methods for further functionality, including the following:
openFile()
: Opens the external file for read-only access.
closeFile()
: Closes the external file.
getBinaryStream()
: Returns the contents of the external file as a stream of bytes.
getBinaryStream(long)
: Returns the contents of the external file as a stream of bytes beginning at the position in the external file specified by the argument.
getBytes()
: Reads from the external file, starting at a specified point, into a supplied buffer.
getName()
: Gets the name of the external file.
getDirAlias()
: Gets the directory alias of the external file.
length()
: Returns the length of the BFILE in bytes.
position()
: Determines the byte position at which the given byte pattern begins.
isFileOpen()
: Determines whether the BFILE is open (for read-only access).
|
Copyright © 1996-2001, Oracle Corporation. All Rights Reserved. |
|