NOTE: Some of the material in this chapter is based on JDBCtm API Tutorial and Reference, Second Edition: Universal Data Access for the Javatm 2 Platform, published by Addison Wesley as part of the Java series, ISBN 0-201-43328-1.
This appendix summarizes the new features that have been added to the JDBC API over time. Note that in order to use a feature, you must be using a driver that supports that feature.
One of the major changes in the JDBC 3.0 API is that it includes the package
javax.sql (the JDBC Optional Package) as well as the package
java.sql. This overview is divided into two sections, the first giving new features introduced in the JDBC 3.0 API for both packages, and the second giving the features introduced in the JDBC 2.0 Optional Package. See the JDBC 3.0 API Specification for more detailed information.
The JDBC 3.0 API introduces new material and changes in these areas:
Savepointinterface, which contains new methods to set a savepoint, to release a savepoint, and to roll back a transaction to a designated savepoint.
Added the ability for deployers to control how prepared statements are pooled and reused by connections.
Defined a number of properties for the
ConnectionPoolDataSourceinterface. These properties can be used to describe how
PooledConnectionobjects created by
DataSourceobjects should be pooled.
Added the new interface
ParameterMetaData, which describes the number, type, and properties of parameters to prepared statements.
Added a means of retrieving values from columns containing automatically generated values.
Added the new method
getMoreResults(int)that takes an argument that specifies whether
ResultSetobjects returned by a
Statementshould be closed before returning any subsequent
CallableStatementobjects by name
Added methods to allow a string to identify the parameter to be set for a
Added the ability to specify whether a
ResultSetobject is kept open after a transaction has been committed.
Added the data type
BOOLEANis logically equivalent to
Added methods to allow the data contained in
Clobobjects to be altered.
Added methods to retrieve the object referenced by a
Refobject. Also added the ability to update a referenced object through the
Addition of the
updateRefmethods to the
Added the data type
java.sql.Types.DATALINK, allowing JDBC drivers to store and retrieve references to external data.
Described the effect of transform groups and how this is reflected in the metadata.
Described the relationship between the JDBC SPI and the connector architecture.
Added metadata for retrieving SQL type hierarchies and various other kinds of information relating to new features.
The following features, which were introduced in the
javax.sql package, are now part of the JDBC 3.0 API and are included in the J2SE version 1.4:
DataSourceObject to Get a Connection
Using the JNDI API and the new
DataSource interface, an application does not need to specify a driver name in its code to make a connection to a data source. It can specify a logical name that has been registered with a JNDI naming service and retrieve a
DataSource object that will get a connection to the desired data source. This capability makes code more portable and much easier to maintain.
Connection pooling allows an application to (re)use database connections that have already been established instead of always having to create new connections. Because creating and destroying database connections is expensive, this feature is important for good performance, especially for server applications.
The JDBC 2.0 Optional Package API provides hooks that allow connection pooling to be implemented on top of the JDBC driver layer. This makes it possible to have a single cache of connections available for all of the JDBC drivers in use.
The JDBC 2.0 Optional Package API allows a JDBC driver to support the standard two-phase commit protocol defined in the Java Transaction API (JTA). This means that a transaction may be distributed over multiple servers, which lets developers write enterprise applications using Enterprise JavaBeanstm components that are transactional across multiple DBMS servers.
RowSet objects are simply containers for tabular data that can be implemented on top of the JDBC API. Rowsets make it possible to pass rows of data across a network, so they are likely to be used extensively in distributed applications. Rowsets may be very lean by being disconnected from a data source, making it possible to display data on a thin client. They also make it possible to use scrolling when the underlying DBMS does not support scrollable result sets. A rowset is a JavaBeanstm component and consequently easy to use in building an application, especially with a development tool.
Typically, a third party will provide a
RowSet implementation, and the application programmer just uses it. The API for a
RowSet implementation is generally very easy to use because most of a rowset's functionality is inherited from the
ResultSet interface. The more complicated aspects of a rowset take place internally and are invisible to the application programmer. There are currently three Early Access implementations of the
RowSet interface available from the Java Developer Connection (
The JDBC 2.0 core API includes the JDBC 1.0 API and adds enhancements and new functionality to it. These additions put the Java programming language at the forefront of database computing, providing both universal data access and improved performance.
Applications that use earlier versions of the JDBC API can be run using the Java 2 platform with no problem, in keeping with the goal of backward compatibility. However, an application that takes advantage of the new 2.0 features must be run with a driver that implements those features.
The new features in the JDBC 2.0 core API fall into two broad categories: support for new functionality and support for the SQL99 data types.
In addition to making the retrieval, storage, and manipulation of data more convenient, the new features make JDBC applications more efficient. For example, batch updates can increase performance dramatically. The new interfaces
Array allow applications to operate on large amounts of data without having to materialize the data on the client, which can mean a significant savings in transfer time and the amount of memory needed. Also, new methods for setting the fetch size and fetch direction let a programmer fine tune an application for more efficient data retrieval and processing.
The JDBC 2.0 core API adds important new functionality. The following sections briefly explain each new area of functionality and summarize the supporting API.
Scrollable result sets provide the ability to move the cursor forward and backward to a specified position or to a position relative to the current position. The following interfaces have new methods that support scrollable result sets.
CallableStatementobjects that make the result sets they produce scrollable
The new batch update facility provides the ability to send multiple updates to the database to be executed as a batch rather than sending each update separately. The following interfaces add methods that support batch updates, and the exception
BatchUpdateException is new.
Programmatic updates provide the ability to make updates using the JDBC API rather than SQL statements. The following interfaces have new methods and constants that support programmatic updates.
updatermethod for updating each data type
The JDBC 2.0 core API provides various other new features, which are summarized in the following list.
ResultSetmethods for getting and setting the current fetch size and fetch direction
CallableStatementmethods for getting and setting the default fetch size and default fetch direction that result sets generated by executing a query will have when they are first created
java.math.BigDecimalvalues-new versions of themethods that retrieve a
java.math.BigDecimalvalue with full precision. Unlike the deprecated versions they replace, these new versions do not take a specified precision.
Calendarobject as a parameter, which allows the driver to use a specified time zone rather than the default when calculating a value for a date, time, or timestamp
The JDBC 2.0 core API adds support for using advanced data types, making it as easy to use them as it is to use simple data types. This support includes the ability to store, retrieve, and update even the new SQL data types that are essentially objects, blurring the distinction between object databases and relational databases. The next four sections ("What Are the SQL99 Data Types?" on page 145, "Summary of Support for the SQL99 Data Types" on page 146, "Mapping of the SQL99 Types" on page 148, and "SQL Locators" on page 149) describe how the JDBC 2.0 core API provides support for these advanced data types.
In addition to being able to store objects defined in SQL as values in a database table, programmers writing Java applications can also store objects defined in the Java programming language as values in a database table. The section "Support for Storing Java Objects" on page 149 describes this capability.
Note that a driver is not required to implement functionality that its DBMS does not support, so not all drivers necessarily implement the functionality described here.
DatabaseMetaData methods such as
getUDTs may be called to get information about which data types a driver supports.
This section briefly describes the new SQL99 data types. Their mapping to types in the Java programming language is described in section A.4.3 on page 148.
The SQL99 data types can be categorized as follows:
DATE, and so on.
)-a reference to the specified SQL structured type
ARRAY[n]-an array of
nelements that are all one data type
The JDBC 2.0 core API supports the SQL 99 data types by means of the following new interfaces, methods, and fields.
gettermethods in the
to retrieve SQL99 type column values from a result set
gettermethods in the
to retrieve SQL99 type values in output parameters
settermethods in the
PreparedStatementinterface to set a SQL99 type column value
updatermethods in the
to update values programmatically
ResultSetMetaDatainterfaces for getting metadata about the SQL99 data types
java.sql.Typesto support new data types and persistent storage
The JDBC API does not try to replicate the SQL99 types exactly; rather, its goal is to map them to types in the Java programming language so that they retain their functionality and are convenient to use. For example, SQL99 has what are called locator types, which are used on a client to designate data that is stored on a database server. Locators can be very useful for dealing with data that is large because they allow the data to be manipulated without having to be materialized on the client machine. SQL99 includes locators for the types
CLOB and structured types. The JDBC API does not include locators for these types directly (and not at all for structured types) but rather provides interfaces that are implemented such that the driver and DBMS use the appropriate locators behind the scenes. The result is that a developer using the JDBC API to access an SQL
CLOB value need not even be aware of locators.
The following SQL99 types are mapped to interfaces in the Java programming language:
Distinct types are not mapped to an interface because they are based on a single built-in type and thus can simply be mapped to the standard mapping for that built-in type. For example, the following is an SQL statement that creates the new type
CREATE TYPE MONEY AS NUMERIC(10, 2)
This new UDT is based on the data type
NUMERIC, which maps to
java.math.BigDecimal, so the type
MONEY maps to
java.math.BigDecimal. This means that a value of type
MONEY would be retrieved with the method
getBigDecimal, stored with the method
setBigDecimal, and updated with the method
LOCATOR is a logical pointer to data that resides on a database server. It typically refers to data that is too large to materialize on the client, such as images or audio. Locators exist only in a client environment, and their existence is transient. A standard implementation will use locators internally for instances of the
Array interfaces. This means that
Array objects contain a locator that points to the data on the server rather than containing the data itself. Programmers operating on
Array instances are actually operating on the database objects they represent. This ability to operate on large database objects without bringing their data to the client is a major plus in performance.
Note that the JDBC API does not call for using the SQL
). In a standard implementation, a
Struct object contains the data of the structured type that it maps and is not implemented internally as a locator, as are
The JDBC API has always supported persistent storage of objects defined in the Java programming language through the methods
setObject. But, of course, persistent storage of Java objects does not actually occur unless a DBMS also supports it. Up to this point, support was limited, but a new generation of DBMSs that recognize Java objects as a data type is emerging. In these DBMSs, termed Java relational DBMSs, an instance of a Java class can be stored as a column value in a database table.