JDBC API Description

  • package java.sql description

    • What the JDBCTM 4.2 API Includes

    • Versions

    • What the java.sql Package Contains

      • Making a connection with a database via the DriverManager facility
      • Sending SQL statements to a database
      • Retrieving and updating the results of a query
      • Standard mappings for SQL types to classes and interfaces in the Java programming language
      • Custom mapping an SQL user-defined type (UDT) to a class in the Java programming language
      • Metadata
      • Exceptions

    • java.sql and javax.sql Features Introduced in the JDBC 4.2 API

    • java.sql and javax.sql Features Introduced in the JDBC 4.1 API

    • java.sql and javax.sql Features Introduced in the JDBC 4.0 API

    • java.sql and javax.sql Features Introduced in the JDBC 3.0 API

    • java.sql Features Introduced in the JDBC 2.1 Core API

    • javax.sql Features Introduced in the JDBC 2.0 Optional Package API

    • Custom Mapping of UDTs

  • Package javax.sql Description

    • Using a DataSource Object to Make a Connection

    • Connection Pooling and Statement Pooling

    • Distributed Transactions

    • Rowsets

      • Event Notification
      • Metadata
      • The Reader/Writer Facility

 

Package java.sql Description

Provides the API for accessing and processing data stored in a data source (usually a relational database) using the JavaTM programming language. This API includes a framework whereby different drivers can be installed dynamically to access different data sources. Although the JDBCTM API is mainly geared to passing SQL statements to a database, it provides for reading and writing data from any data source with a tabular format. The reader/writer facility, available through the javax.sql.RowSet group of interfaces, can be customized to use and update data from a spread sheet, flat file, or any other tabular data source.

 

What the JDBCTM 4.2 API Includes

The JDBCTM 4.2 API includes both the java.sql package, referred to as the JDBC core API, and the javax.sql package, referred to as the JDBC Optional Package API. This complete JDBC API is included in the JavaTM Standard Edition (Java SETM), version 7. The javax.sql package extends the functionality of the JDBC API from a client-side API to a server-side API, and it is an essential part of the JavaTM Enterprise Edition (Java EETM) technology.

 

Versions

The JDBC 4.2 API incorporates all of the previous JDBC API versions:
  • The JDBC 4.1 API
  • The JDBC 4.0 API
  • The JDBC 3.0 API
  • The JDBC 2.1 core API
  • The JDBC 2.0 Optional Package API
    (Note that the JDBC 2.1 core API and the JDBC 2.0 Optional Package API together are referred to as the JDBC 2.0 API.)
  • The JDBC 1.2 API
  • The JDBC 1.0 API

Classes, interfaces, methods, fields, constructors, and exceptions have the following "since" tags that indicate when they were introduced into the Java platform. When these "since" tags are used in JavadocTM comments for the JDBC API, they indicate the following:

  • Since 1.8 -- new in the JDBC 4.2 API and part of the Java SE platform, version 8
  • Since 1.7 -- new in the JDBC 4.1 API and part of the Java SE platform, version 7
  • Since 1.6 -- new in the JDBC 4.0 API and part of the Java SE platform, version 6
  • Since 1.4 -- new in the JDBC 3.0 API and part of the J2SE platform, version 1.4
  • Since 1.2 -- new in the JDBC 2.0 API and part of the J2SE platform, version 1.2
  • Since 1.1 or no "since" tag -- in the original JDBC 1.0 API and part of the JDKTM, version 1.1

NOTE: Many of the new features are optional; consequently, there is some variation in drivers and the features they support. Always check your driver's documentation to see whether it supports a feature before you try to use it.

NOTE: The class SQLPermission was added in the JavaTM 2 SDK, Standard Edition, version 1.3 release. This class is used to prevent unauthorized access to the logging stream associated with the DriverManager, which may contain information such as table names, column data, and so on.

 

What the java.sql Package Contains

The java.sql package contains API for the following:
  • Making a connection with a database via the DriverManager facility
    • DriverManager class -- makes a connection with a driver
    • SQLPermission class -- provides permission when code running within a Security Manager, such as an applet, attempts to set up a logging stream through the DriverManager
    • Driver interface -- provides the API for registering and connecting drivers based on JDBC technology ("JDBC drivers"); generally used only by the DriverManager class
    • DriverPropertyInfo class -- provides properties for a JDBC driver; not used by the general user
  • Sending SQL statements to a database
    • Statement -- used to send basic SQL statements
    • PreparedStatement -- used to send prepared statements or basic SQL statements (derived from Statement)
    • CallableStatement -- used to call database stored procedures (derived from PreparedStatement)
    • Connection interface -- provides methods for creating statements and managing connections and their properties
    • Savepoint -- provides savepoints in a transaction
  • Retrieving and updating the results of a query
    • ResultSet interface
  • Standard mappings for SQL types to classes and interfaces in the Java programming language
    • Array interface -- mapping for SQL ARRAY
    • Blob interface -- mapping for SQL BLOB
    • Clob interface -- mapping for SQL CLOB
    • Date class -- mapping for SQL DATE
    • NClob interface -- mapping for SQL NCLOB
    • Ref interface -- mapping for SQL REF
    • RowId interface -- mapping for SQL ROWID
    • Struct interface -- mapping for SQL STRUCT
    • SQLXML interface -- mapping for SQL XML
    • Time class -- mapping for SQL TIME
    • Timestamp class -- mapping for SQL TIMESTAMP
    • Types class -- provides constants for SQL types
  • Custom mapping an SQL user-defined type (UDT) to a class in the Java programming language
    • SQLData interface -- specifies the mapping of a UDT to an instance of this class
    • SQLInput interface -- provides methods for reading UDT attributes from a stream
    • SQLOutput interface -- provides methods for writing UDT attributes back to a stream
  • Metadata
    • DatabaseMetaData interface -- provides information about the database
    • ResultSetMetaData interface -- provides information about the columns of a ResultSet object
    • ParameterMetaData interface -- provides information about the parameters to PreparedStatement commands
  • Exceptions
    • SQLException -- thrown by most methods when there is a problem accessing data and by some methods for other reasons
    • SQLWarning -- thrown to indicate a warning
    • DataTruncation -- thrown to indicate that data may have been truncated
    • BatchUpdateException -- thrown to indicate that not all commands in a batch update executed successfully

 

java.sql and javax.sql Features Introduced in the JDBC 4.2 API

  • Added JDBCType enum and SQLType interface
  • Support for REF CURSORS in CallableStatement
  • DatabaseMetaData methods to return maximum Logical LOB size and if Ref Cursors are supported
  • Added support for large update counts

 

java.sql and javax.sql Features Introduced in the JDBC 4.1 API

  • Allow Connection, ResultSet and Statement objects to be used with the try-with-resources statement
  • Supported added to CallableStatement and ResultSet to specify the Java type to convert to via the getObject method
  • DatabaseMetaData methods to return PseudoColumns and if a generated key is always returned
  • Added support to Connection to specify a database schema, abort and timeout a physical connection.
  • Added support to close a Statement object when its dependent objects have been closed
  • Support for obtaining the parent logger for a Driver, DataSource, ConnectionPoolDataSource and XADataSource

java.sql and javax.sql Features Introduced in the JDBC 4.0 API

  • auto java.sql.Driver discovery -- no longer need to load a java.sql.Driver class via Class.forName
  • National Character Set support added
  • Support added for the SQL:2003 XML data type
  • SQLException enhancements -- Added support for cause chaining; New SQLExceptions added for common SQLState class value codes
  • Enhanced Blob/Clob functionality -- Support provided to create and free a Blob/Clob instance as well as additional methods added to improve accessibility
  • Support added for accessing a SQL ROWID
  • Support added to allow a JDBC application to access an instance of a JDBC resource that has been wrapped by a vendor, usually in an application server or connection pooling environment.
  • Availability to be notified when a PreparedStatement that is associated with a PooledConnection has been closed or the driver determines is invalid

 

 

java.sql and javax.sql Features Introduced in the JDBC 3.0 API

  • Pooled statements -- reuse of statements associated with a pooled connection
  • Savepoints -- allow a transaction to be rolled back to a designated savepoint
  • Properties defined for ConnectionPoolDataSource -- specify how connections are to be pooled
  • Metadata for parameters of a PreparedStatement object
  • Ability to retrieve values from automatically generated columns
  • Ability to have multiple ResultSet objects returned from CallableStatement objects open at the same time
  • Ability to identify parameters to CallableStatement objects by name as well as by index
  • ResultSet holdability -- ability to specify whether cursors should be held open or closed at the end of a transaction
  • Ability to retrieve and update the SQL structured type instance that a Ref object references
  • Ability to programmatically update BLOB, CLOB, ARRAY, and REF values.
  • Addition of the java.sql.Types.DATALINK data type -- allows JDBC drivers access to objects stored outside a data source
  • Addition of metadata for retrieving SQL type hierarchies

 

java.sql Features Introduced in the JDBC 2.1 Core API

  • Scrollable result sets--using new methods in the ResultSet interface that allow the cursor to be moved to a particular row or to a position relative to its current position
  • Batch updates
  • Programmatic updates--using ResultSet updater methods
  • New data types--interfaces mapping the SQL3 data types
  • Custom mapping of user-defined types (UDTs)
  • Miscellaneous features, including performance hints, the use of character streams, full precision for java.math.BigDecimal values, additional security, and support for time zones in date, time, and timestamp values.

 

javax.sql Features Introduced in the JDBC 2.0 Optional Package API

  • The DataSource interface as a means of making a connection. The Java Naming and Directory InterfaceTM (JNDI) is used for registering a DataSource object with a naming service and also for retrieving it.
  • Pooled connections -- allowing connections to be used and reused
  • Distributed transactions -- allowing a transaction to span diverse DBMS servers
  • RowSet technology -- providing a convenient means of handling and passing data

 

 

Custom Mapping of UDTs

A user-defined type (UDT) defined in SQL can be mapped to a class in the Java programming language. An SQL structured type or an SQL DISTINCT type are the UDTs that may be custom mapped. The following three steps set up a custom mapping:
  1. Defining the SQL structured type or DISTINCT type in SQL
  2. Defining the class in the Java programming language to which the SQL UDT will be mapped. This class must implement the SQLData interface.
  3. Making an entry in a Connection object's type map that contains two things:
    • the fully-qualified SQL name of the UDT
    • the Class object for the class that implements the SQLData interface

When these are in place for a UDT, calling the methods ResultSet.getObject or CallableStatement.getObject on that UDT will automatically retrieve the custom mapping for it. Also, thePreparedStatement.setObject method will automatically map the object back to its SQL type to store it in the data source.

 

Package javax.sql Description

Provides the API for server side data source access and processing from the JavaTM programming language. This package supplements the java.sql package and, as of the version 1.4 release, is included in the Java Platform, Standard Edition (Java SETM). It remains an essential part of the Java Platform, Enterprise Edition (Java EETM).

The javax.sql package provides for the following:

  1. The DataSource interface as an alternative to the DriverManager for establishing a connection with a data source
  2. Connection pooling and Statement pooling
  3. Distributed transactions
  4. Rowsets

Applications use the DataSource and RowSet APIs directly, but the connection pooling and distributed transaction APIs are used internally by the middle-tier infrastructure.

Using a DataSource Object to Make a Connection

The javax.sql package provides the preferred way to make a connection with a data source. The DriverManager class, the original mechanism, is still valid, and code using it will continue to run. However, the newer DataSource mechanism is preferred because it offers many advantages over the DriverManager mechanism.

These are the main advantages of using a DataSource object to make a connection:

  • Changes can be made to a data source's properties, which means that it is not necessary to make changes in application code when something about the data source or driver changes.
  • Connection and Statement pooling and distributed transactions are available through a DataSource object that is implemented to work with the middle-tier infrastructure. Connections made through the DriverManager do not have connection and statement pooling or distributed transaction capabilities.

Driver vendors provide DataSource implementations. A particular DataSource object represents a particular physical data source, and each connection the DataSource object creates is a connection to that physical data source.

A logical name for the data source is registered with a naming service that uses the Java Naming and Directory InterfaceTM (JNDI) API, usually by a system administrator or someone performing the duties of a system administrator. An application can retrieve the DataSource object it wants by doing a lookup on the logical name that has been registered for it. The application can then use the DataSource object to create a connection to the physical data source it represents.

A DataSource object can be implemented to work with the middle tier infrastructure so that the connections it produces will be pooled for reuse. An application that uses such a DataSourceimplementation will automatically get a connection that participates in connection pooling. A DataSource object can also be implemented to work with the middle tier infrastructure so that the connections it produces can be used for distributed transactions without any special coding.

Connection Pooling and Statement Pooling

Connections made via a DataSource object that is implemented to work with a middle tier connection pool manager will participate in connection pooling. This can improve performance dramatically because creating new connections is very expensive. Connection pooling allows a connection to be used and reused, thus cutting down substantially on the number of new connections that need to be created.

Connection pooling is totally transparent. It is done automatically in the middle tier of a Java EE configuration, so from an application's viewpoint, no change in code is required. An application simply uses the DataSource.getConnection method to get the pooled connection and uses it the same way it uses any Connection object.

The classes and interfaces used for connection pooling are:

  • ConnectionPoolDataSource
  • PooledConnection
  • ConnectionEvent
  • ConnectionEventListener
  • StatementEvent
  • StatementEventListener
The connection pool manager, a facility in the middle tier of a three-tier architecture, uses these classes and interfaces behind the scenes. When a ConnectionPoolDataSource object is called on to create a PooledConnection object, the connection pool manager will register as a ConnectionEventListener object with the new PooledConnection object. When the connection is closed or there is an error, the connection pool manager (being a listener) gets a notification that includes a ConnectionEvent object.

If the connection pool manager supports Statement pooling, for PreparedStatements, which can be determined by invoking the method DatabaseMetaData.supportsStatementPooling, the connection pool manager will register as a StatementEventListener object with the new PooledConnection object. When the PreparedStatement is closed or there is an error, the connection pool manager (being a listener) gets a notification that includes a StatementEvent object.

 

Distributed Transactions

As with pooled connections, connections made via a DataSource object that is implemented to work with the middle tier infrastructure may participate in distributed transactions. This gives an application the ability to involve data sources on multiple servers in a single transaction.

The classes and interfaces used for distributed transactions are:

  • XADataSource
  • XAConnection
These interfaces are used by the transaction manager; an application does not use them directly.

The XAConnection interface is derived from the PooledConnection interface, so what applies to a pooled connection also applies to a connection that is part of a distributed transaction. A transaction manager in the middle tier handles everything transparently. The only change in application code is that an application cannot do anything that would interfere with the transaction manager's handling of the transaction. Specifically, an application cannot call the methods Connection.commit or Connection.rollback, and it cannot set the connection to be in auto-commit mode (that is, it cannot call Connection.setAutoCommit(true)).

An application does not need to do anything special to participate in a distributed transaction. It simply creates connections to the data sources it wants to use via theDataSource.getConnection method, just as it normally does. The transaction manager manages the transaction behind the scenes. The XADataSource interface creates XAConnectionobjects, and each XAConnection object creates an XAResource object that the transaction manager uses to manage the connection.

Rowsets

The RowSet interface works with various other classes and interfaces behind the scenes. These can be grouped into three categories.
  1. Event Notification
    • RowSetListener
      A RowSet object is a JavaBeansTM component because it has properties and participates in the JavaBeans event notification mechanism. The RowSetListener interface is implemented by a component that wants to be notified about events that occur to a particular RowSet object. Such a component registers itself as a listener with a rowset via theRowSet.addRowSetListener method.

      When the RowSet object changes one of its rows, changes all of it rows, or moves its cursor, it also notifies each listener that is registered with it. The listener reacts by carrying out its implementation of the notification method called on it.

       

    • RowSetEvent
      As part of its internal notification process, a RowSet object creates an instance of RowSetEvent and passes it to the listener. The listener can use this RowSetEvent object to find out which rowset had the event.

     

  2. Metadata
    • RowSetMetaData
      This interface, derived from the ResultSetMetaData interface, provides information about the columns in a RowSet object. An application can use RowSetMetaData methods to find out how many columns the rowset contains and what kind of data each column can contain.

      The RowSetMetaData interface provides methods for setting the information about columns, but an application would not normally use these methods. When an application calls the RowSet method execute, the RowSet object will contain a new set of rows, and its RowSetMetaData object will have been internally updated to contain information about the new columns.

       

  3. The Reader/Writer Facility
    A RowSet object that implements the RowSetInternal interface can call on the RowSetReader object associated with it to populate itself with data. It can also call on the RowSetWriterobject associated with it to write any changes to its rows back to the data source from which it originally got the rows. A rowset that remains connected to its data source does not need to use a reader and writer because it can simply operate on the data source directly.
    • RowSetInternal
      By implementing the RowSetInternal interface, a RowSet object gets access to its internal state and is able to call on its reader and writer. A rowset keeps track of the values in its current rows and of the values that immediately preceded the current ones, referred to as the original values. A rowset also keeps track of (1) the parameters that have been set for its command and (2) the connection that was passed to it, if any. A rowset uses the RowSetInternal methods behind the scenes to get access to this information. An application does not normally invoke these methods directly.

       

    • RowSetReader
      A disconnected RowSet object that has implemented the RowSetInternal interface can call on its reader (the RowSetReader object associated with it) to populate it with data. When an application calls the RowSet.execute method, that method calls on the rowset's reader to do much of the work. Implementations can vary widely, but generally a reader makes a connection to the data source, reads data from the data source and populates the rowset with it, and closes the connection. A reader may also update theRowSetMetaData object for its rowset. The rowset's internal state is also updated, either by the reader or directly by the method RowSet.execute.
    • RowSetWriter
      A disconnected RowSet object that has implemented the RowSetInternal interface can call on its writer (the RowSetWriter object associated with it) to write changes back to the underlying data source. Implementations may vary widely, but generally, a writer will do the following:

       

      • Make a connection to the data source
      • Check to see whether there is a conflict, that is, whether a value that has been changed in the rowset has also been changed in the data source
      • Write the new values to the data source if there is no conflict
      • Close the connection

The RowSet interface may be implemented in any number of ways, and anyone may write an implementation. Developers are encouraged to use their imaginations in coming up with new ways to use rowsets.

IMPORTANT NOTE: Code that uses API marked "Since 1.6" must be run using a JDBC technology driver that implements the JDBC 4.0 API. You must check your driver documentation to be sure that it implements the particular features you want to use.

 

posted @ 2016-01-25 12:15  乐享程序员  阅读(611)  评论(0)    收藏  举报