Marcin Luckner Warsaw University of Technology Faculty of Mathematics and Information Science

Transcription

1 Marcin Luckner Warsaw University of Technology Faculty of Mathematics and Information Science

2 } JDBC ("Java Database Connectivity ) is a set of API function which can e used for calling SQL commands lets us write database applications in pure java is safe and simple 2

3 3

4 } (Open DataBase Connectivity) ODBC contains callings of procedures written in C it is not possible to transform ODBC to Java ODBC is quite complicated and learning it may be difficult ODBC needs manual configuration of a driver on each computer 4

5 5

6 } bridge JDBC-ODBC + ODBC driver Data is sent by an ODBC driver. ODBC binaries must be installed on each client. } native API + partial JDBC Java calls directly native functions of a given DBMS. Binaries must be installed on each client. } network JDBC + pure Java JDBC Driver translates queries into DBMS independent code, which is sent to a server. } native protocol + pure Java Makes direct connection between Java application and a database. 6

7 } made by Driver class } it creates a Connection object representing the connection } DriverManager class loads drivers and chooses the right one } usually the method getconection is called } chosen driver can be also called directly Connection Driver.connect(String url, Properties info) 7

8 } general definition jdbc:<subprotocol>:<subname> 1. protocol - always JDBC 2. subprotocol - name of a driver or a connection description. Can be done by several different drivers. 3. subname - depends on a driver. Identifies the connection, must provide enough information for establishing a connection. Usually//hostname:port/subsubname is used. 8

9 } JDBC Thin Driver (no local SQL*Net installation required/ handy for applets) } JDBC OCI for writing stand-alone Java applications } JDBC KPRB driver (default connection) for Java Stored Procedures and Database JSPs. 9

10 } Thin driver 10

11 } SUN has created a JDBC bridge to an ODBC driver } ODBC must be configured on a client machine } general form: jdbc:odbc:<data-source-name>[;<attribute-name>=<attribute-value>]* 11

12 } Connection creates three classes of objects Statement - (createstatement method) sends simple queries PreparedStatement - (preparestatement method) can additionally send query input parameters. It extends capabilities of simple queries. It can work more effectively due to a fact that it precompiles the query before the execution. CallableStatement - (preparecall method) Calls server stored procedures. It can pass parameters and receive results. 12

13 13

14 } used for calling queries and retrieving results } only one result set may be opened at a time } each call of execute closes actual result set 14

15 } void cancel() cancels the query } void close() closes query and frees resources } boolean execute(string sql) calls a query which can return many result set } ResultSet executequery(string sql) calls query which returns only one result set } int executeupdate(string sql) for calling INSERT, UPDATE, DELETE. } boolean getmoreresults() moves to the next result set } ResultSet getresultset() returns the query result set } SQLWarning getwarnings() return warnings generated by the query 15

16 } represents precompiled queries } it can be executed in a loop with increased effectiveness } parameters can be inserted into queries by replacing values with? signs } parameters are defined with setx(...) method giving parameter's index and the value } the type of setx(...) must be exactly the same as the value type expected in the query } all input parameters must be defined before the execution of the query 16

17 17

18 } tool for gaining many return values from a single query } each return value must be registered with registeroutparameter(int paramindex, int sqltype) method } possible types of parameters are collected in java.sql.types } parameter can be input and output in the same time (setx(...)) 18

19 19

20 20

21 } represents two dimensional array, where rows are result records and columns are data fields } moving between records is done with the next() and previous() method } at the beginning cursor is set on the row 'before' the first one } values from columns can be retrieved with getx( int colindex ) and getx( String colname ) methods } the first method is suggested because columns in SQL not always have names } data is accessible until the source query or result set is closed 21

22 22

23 23

24 } connection, result sets and queries should always be closed by calling the close() method } it immediately frees resources and sends message to the DBMS system } some applets can be killed before normal execution of Garbage Collector 24

25 } drivers are managed by DriverManager } each driver in its static part should create and register an instance of itself } there is no need to register it manually } loading a driver by calling Class.forName( PackageName.Driver"); by adding driver's name to the driver list (jdbc.drivers) in java.lang.system (using setproperty( String name, String value) ) method It is a semicolon-separated list separated of classes the first calling to DriverManager (at the beginning of the application) loads drivers from the list the list is not searched again 25

26 } OCI driver Class.forName ("oracle.jdbc.oracledriver"); Connection conn = DriverManager.getConnection ("jdbc:oracle:oci8:@hostname_orcl", "scott", "tiger"); // or userid, password 26

27 } some sequence of statements that can be committed or cancelled } by default JDBC works in auto-commit mode } the mode can be changed with the Connection.setAutoCommit(boolean auto) method } accepting / cancelling transaction is done with commit() / rollback() methods } a driver must be transaction capable 27