Once you run your query, use the next method of the ResultSet object to iterate through the results. This method steps through the result set row by row, detecting the end of the result set when it is reached. For example, the following code will iterate through the ResultSet object, rset , from the previous section and will retrieve and print each employee name:.
The next method returns false when it reaches the end of the result set. The employee names are materialized as Java String values. You must explicitly close the ResultSet and Statement objects after you finish using them. The drivers do not have finalizer methods. The cleanup routines are performed by the close method of the ResultSet and Statement classes.
If you do not explicitly close the ResultSet and Statement objects, serious memory leaks could occur. You could also run out of cursors in the database. Closing both the result set and the statement releases the corresponding cursor in the database. If you close only the result set, then the cursor is not released. For example, if your ResultSet object is rset and your Statement object is stmt , then close the result set and statement with the following lines of code:.
When you close a Statement object that a given Connection object creates, the connection itself remains open. PreparedStatement objects enable you to run a statement with varying sets of input parameters. Use the set XXX methods on the PreparedStatement object to bind data to the prepared statement to be sent to the database. To perform data definition language DDL operations, you can create either a Statement object or a PreparedStatement object. The following example shows how to create a table in the database using a Statement object.
If your code involves reexecuting a DDL operation, then, before reexecuting the statement, you must prepare it again. The following example shows how to prepare your DDL statements before any reexecution:. By default, data manipulation language DML operations are committed automatically as soon as they are run.
This is known as the auto-commit mode. However, you can disable auto-commit mode with the following method call on the Connection object:. If you disable the auto-commit mode, then you must manually commit or roll back changes with the appropriate method call on the Connection object:.
If the auto-commit mode is disabled and you close the connection without explicitly committing or rolling back your last changes, then an implicit COMMIT operation is run. When a transaction updates the database, it generates a redo entry corresponding to this update. Oracle Database buffers this redo in memory until the completion of the transaction. When you commit the transaction, the Log Writer LGWR process writes the redo entry for the commit to disk, along with the accumulated redo entries of all changes in the transaction.
By default, Oracle Database writes the redo to disk before the call returns to the client. This behavior introduces latency in the commit because the application must wait for the redo entry to be persisted on disk. If your application requires very high transaction throughput and you are willing to trade commit durability for lower commit latency, then you can change the behavior of the default COMMIT operation, depending on the needs of your application.
Whether the Log Writer should batch the call or not. You can also combine different options together. For example:.
You must close the connection to the database after you have performed all the required operations and no longer require the connection. You can close the connection by using the close method of the Connection object, as follows:. The steps in the preceding sections are illustrated in the following example, which uses the Oracle JDBC Thin driver to create a data source, connects to the database, creates a Statement object, runs a query, and processes the result set.
Note that the code for creating the Statement object, running the query, returning and processing the ResultSet object, and closing the statement and connection uses the standard JDBC API. That is, you have written call specifications to publish them to the Oracle data dictionary. Applications can call Java stored procedures using the Native Java Interface for direct invocation of static Java methods.
SQLException class or its subclass. Errors can originate either in the JDBC driver or in the database itself. Resulting messages describe the error and identify the method that threw the error. Additional run-time information can also be appended. JDBC 3. However, there are large categories of errors and it is useful to distinguish them. Therefore, in JDBC 4.
It is used for code that runs on the database server and accesses the same session. That is, the code runs and accesses data from a single Oracle session. The server-side internal drivers support only JDK 1. All the JDBC drivers support the following standards and features:.
Oracle JDBC drivers implement the standard java. You can access the Oracle-specific features, in addition to the standard features, by using the oracle. It is platform-independent and does not require any additional Oracle software on the client-side. It requires an Oracle client installation and, therefore, is Oracle platform-specific.
OCI is an API that enables you to create applications that use the native procedures or function calls of a third-generation language to access Oracle Database and control all phases of the SQL statement processing. However, the JDBC server-side Thin driver runs inside Oracle Database and accesses a remote database or a different session on the same database. The use of JDBC Thin driver from a client application or from inside a server does not affect the code. The JDBC server-side internal driver supports any Java code that runs inside Oracle Database, such as in a Java stored procedure, and must access the same database.
This driver supports only JDK 1. The programs access the SQL engine by using function calls. The JDBC server-side internal driver is fully consistent with the client-side drivers and supports the same features and extensions. The Oracle packages listed as optional provide access to the extended functionality provided by Oracle JDBC drivers, but are not required for the example presented in this section. First, you must create an OracleDataSource instance.
Then, open a connection to the database using the OracleDataSource. The properties of the retrieved connection are derived from the OracleDataSource instance. The following example connects user HR with password hr to a database with service orcl through port of the host myhost , using the JDBC Thin driver:.
In this case, the URL includes the user name and password and is the only input parameter. If you want to connect using the Thin driver, then you must specify the port number. Once you connect to the database and, in the process, create a Connection object, the next step is to create a Statement object. To continue the example from the previous section, where the Connection object conn was created, here is an example of how to create the Statement object:.
To query the database, use the executeQuery method of the Statement object. The method used to execute a Statement object depends on the type of SQL statement being executed. If the type of the SQL statement is not known, the execute method should be used. Once you run your query, use the next method of the ResultSet object to iterate through the results. This method steps through the result set row by row, detecting the end of the result set when it is reached.
For example, the following code will iterate through the ResultSet object, rset , from the previous section and will retrieve and print each employee name:. The next method returns false when it reaches the end of the result set. The employee names are materialized as Java String values. You must explicitly close the ResultSet and Statement objects after you finish using them.
The drivers do not have finalizer methods. The cleanup routines are performed by the close method of the ResultSet and Statement classes. If you do not explicitly close the ResultSet and Statement objects, serious memory leaks could occur. You could also run out of cursors in the database.
Closing both the result set and the statement releases the corresponding cursor in the database. If you close only the result set, then the cursor is not released. For example, if your ResultSet object is rset and your Statement object is stmt , then close the result set and statement with the following lines of code:. When you close a Statement object that a given Connection object creates, the connection itself remains open.
PreparedStatement objects enable you to run a statement with varying sets of input parameters. Use the set XXX methods on the PreparedStatement object to bind data to the prepared statement to be sent to the database. To perform data definition language DDL operations, you must create a Statement object.
The following example shows how to create a table in the database:. Also, due to a Database limitation, if you use a PreparedStatement object for a DDL operation, then it only works for the first time it is executed. So, you should use only Statement objects for DDL operations.
By default, data manipulation language DML operations are committed automatically as soon as they are run. This is known as the auto-commit mode. When auto-commit status is set to true and commit or rollback method is called. When the default status of auto-commit is not changed and commit or rollback method is called. However, you can disable auto-commit mode with the following method call on the Connection object:. If you disable the auto-commit mode, then you must manually commit or roll back changes with the appropriate method call on the Connection object:.
If the auto-commit mode is disabled and you close the connection without explicitly committing or rolling back your last changes, then an implicit COMMIT operation is run. When a transaction updates the database, it generates a redo entry corresponding to this update. Oracle Database buffers this redo in memory until the completion of the transaction. When you commit the transaction, the Log Writer LGWR process writes the redo entry for the commit to disk, along with the accumulated redo entries of all changes in the transaction.
By default, Oracle Database writes the redo to disk before the call returns to the client. This behavior introduces latency in the commit because the application must wait for the redo entry to be persisted on disk. If your application requires very high transaction throughput and you are willing to trade commit durability for lower commit latency, then you can change the behavior of the default COMMIT operation, depending on the needs of your application. Whether the Log Writer should batch the call or not.
You can also combine different options together. For example:. Starting from this release, Oracle Database supports invisible columns.
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