Java Database Connectivity

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Advanced Java Prgramming Curse Java Database Cnnectivity Sessin bjectives JDBC basic Wrking with JDBC Advanced JDBC prgramming By Võ Văn Hải Faculty f Infrmatin

access and manipulate different kinds f database. Defines the way hw DB and applicatin cmmunicate with each ther.

1 Advanced Java Prgramming Curse Java Database Cnnectivity Sessin bjectives JDBC basic Wrking with JDBC Advanced JDBC prgramming By Võ Văn Hải Faculty f Infrmatin Technlgies Industrial University f H Chi Minh City 2 Definitins f JDBC JDBC basic Part 1 JDBC APIs, which prvides a set f classes and interfaces written in Java t access and manipulate different kinds f database. Defines the way hw DB and applicatin cmmunicate with each ther. JDBC APIs has implementatin separately by set f classes fr a specific DB engine knwn as JDBC driver. Define hw a cnnectin is pened Hw requests are cmmunicated t a DB Hw SQL queries are executed, the query results retrieved

Advantages f JDBC Hw Applicatin and Backend Database cmmunicate?

DBMS Vendr independent Thanks t the cmbinatin f Java API and the JDBC

JDBC driver is base f JDBC API Respnsible fr ensuring that an applicatin

a DB understandable, native frmat and then presents it t the DB Handled

2 Advantages f JDBC Hw Applicatin and Backend Database cmmunicate? Cntinued usage f existing data Even if the data is stred n different DBMS Vendr independent Thanks t the cmbinatin f Java API and the JDBC API Platfrm independent Ease f use 5 6 JDBC Drivers Types f JDBC driver JDBC driver is base f JDBC API Respnsible fr ensuring that an applicatin has a cnsistent and unifrm access t any DB Cnverts the client request t a DB understandable, native frmat and then presents it t the DB Handled DB respnse, and gets cnverted t the Java frmat and presented t the client /44 2

Tw-Tier Data Prcessing Mdel Three-Tier Data Prcessing Mdel The client cmmunicates directly t the DB server withut the help f any middle-ware technlgies r anther server.

The DB server prcesses the request Then DB server sent back the results t the middle tier which again sends it t the client. 9 10 JDBC Applicatin Develpment Prcess 1.

3 Tw-Tier Data Prcessing Mdel Three-Tier Data Prcessing Mdel The client cmmunicates directly t the DB server withut the help f any middle-ware technlgies r anther server. JDBC API translate and sent the client request t the DB. The result are delivered back t the client again thugh the JDBC API The middle-tier is emplyed t send the client request t the DB server. The DB server prcesses the request Then DB server sent back the results t the middle tier which again sends it t the client JDBC Applicatin Develpment Prcess 1. Register and Lading the JDBC driver with DriverManager 2. Establish a DB cnnectin 3. Create a SQL statement 4. Execute a SQL statement #1/6: Lading and register the JDBC driver with DriverManager DriverManager class Manages the set f JDBC drivers available fr an applicatin. Class.frName() methd T create an instance f the specified driver class Register it with the DriverManager class. Syntax: Class.frName ( <driver> ); Ppular drivers: 5. Prcess the SQL Query results 6. Clse the DB cnnectin

#2/6: Establishing Database Cnnectin Use getcnnectin() methd f DriverManager class Cnnectin URL: Syn taxprtcl : <subprtcl> : <subname> 1. prtcl: prtcl name fr accessing the DB 2.

4 #2/6: Establishing Database Cnnectin Use getcnnectin() methd f DriverManager class Cnnectin URL: Syn taxprtcl : <subprtcl> : <subname> 1. prtcl: prtcl name fr accessing the DB 2. subprtcl: recgnizes the underlying DB surce 3. subname: identifies the DB name Syntax: Establishing Database Cnnectin Example: Cnnect t Ms Access Ppular URL #3/6: Creating a SQL Statement Statement bject represent a cmmand send t the database fr query executin Three categries f Statement 1. Statement: Execute SQL queries with n parameters t be parsed. 2. PreparedStatement: Execute a precmplied SQL statement with r withut IN parameters 3. CallableStatement: Execute a call t stre prcedure. Samples: #4/6: Execute a SQL statement Execute methds f Statement bject: executeupdate: exec a nn return value query (delete,insert,update queries). executequery: execute and return a set f recrds. executebatch: execute a batch f cmmands. execute: multipurpse cmmand t execute any types f SQL cmmand. Example:

#5/6 - Prcess the SQL Query results ResultSet bject Represent as ResultSet bject A table f data representing a database result set Generated by executing a SQL SELECT statement In the beginning, the

5 #5/6 - Prcess the SQL Query results ResultSet bject Represent as ResultSet bject A table f data representing a database result set Generated by executing a SQL SELECT statement In the beginning, the cursr is psitined befre the first rw. The next() methd mves the cursr t the next rw Returns false when there are n mre rws in the ResultSet bject A default ResultSet bject is nt updatable and has a cursr that mves frward nly ResultSet bject : Get a set f recrds after execute a select sql cmmand. ResultSet rs = statement.executequery(sql); Using getxxx() methds t get specify values frm ResultSet String id=rs. getstring( StudentID ); Parameters in getxxx() methds can be a database field name r the index f DB field. Database clumn numbers start at 1. Each getxxx() methd will make reasnable type cnversins when the type f the methd desn't match the type f the clumn. SQL data types and Java data types are nt exactly the same 17 17/44 18 SQL data type vs. Java data type ResultSet example

Batch Updates #6/6: Clsing the Database Cnnectin Batch Update allws t submit multiple update cmmands tgether as a single unit, r batch, t the underlying DBMS.

6 Batch Updates #6/6: Clsing the Database Cnnectin Batch Update allws t submit multiple update cmmands tgether as a single unit, r batch, t the underlying DBMS. The cmmands in a batch can be actins such as INSERT, UPDATE, and DELETE.Hwever, yu cannt add SELECT cmmands t a batch. T execute a batch, yu first create a Statement/PreparedStatement bject in the usual way: Statement statement = cnn.createstatement(); Nw, instead f calling executeupdate, yu call the addbatch methd: String sqlcmmand = "..." statement.addbatch(sqlcmmand); Finally, yu submit the entire batch: int[] cunts = stat.executebatch(); Use clse() methd f Cnnectin, Statement, ResultSet bject. Database cnnectins shuld be clsed within a finally blck /44 Execute queries Wrking with JDBC Part 2 Execute select sql statement : Execute insert,update, delete sql statement

7 Execute sql statement with parameters Using parameters in yur sql statement likes sample fllw : String psql= select * frm tblclass where classid=? where? replace fr an parameter T passing parameter in this case, we must use PrepareStatement bjecct instead f using Statement bject. PreparedStatement pstmt=cn.preparestatement(psql); Befre executing the prepared statement, yu must bind the hst variables t actual values with a setxxx() methd. Ex: setstring(1, CDTH4C ); The psitin 1 dentes the first? and s n. 25 Scrllable and Updatable Result Sets Scrllable Scrllable Result Set Refers t capability t mve frward, backward r g directly t a specific rw. ResultSet type TYPE_FORWARD_ONLY Descriptin Fr a ResultSet bject whse cursr may mve nly frward. TYPE_SCROLL_INSENSITIVE Fr a ResultSet bject that is scrllable but generally nt sensitive t changes made by thers. TYPE_SCROLL_SENSITIVE Fr a ResultSet bject that is scrllable and generally sensitive t changes made by thers. 26 Scrllable and Updatable Result Sets Updatable Updatable Result Set Allw change the data in the existing rw, t insert a new rw, r delete an existing rw then cpy the changes t the database. The cncurrency type f a result set determines whether it is updatable r nt. Cncurrency name CONCUR_READ_ONLY CONCUR_UPDATABLE Descriptin Fr a ResultSet bject that may NOT be updated. Fr a ResultSet bject that may be updated. Scrllable and Updatable Result Sets T btain scrlling result sets frm yur queries, yu must btain a different Statement bject with the methd: Statement stat = cnn.createstatement(rs_type, cncurrency); Fr a prepared statement, use the call PreparedStatement stat = cnn.preparestatement( cmmand, rs_type, cncurrency); Example: Statement stmt = cnn.createstatement( ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_READ_ONLY); ResultSet rs=stmt.executequery(sql);

8 Scrllable and Updatable Result Sets Scrllable Result Set Scrllable and Updatable Result Sets Updatable Result Set After create the scrllable ResultSet, we can scrlling is very simple: rs.next(); //mve next recrd. rs.previus(); //mve previus recrd. rs.first(); //mve t first recrd. rs.last(); //mve t last recrd. rs.relative(n); //mve the cursr ver n recrd(s). rs.abslute(n); //set the cursr t a rw n th. int n = rs.getrw();//gets the number f the current rw //Rws are numbered starting with 1. rs.befrefirst();//befre the first psitin. rs.afterlast();// after the last psitin. Update the rw under the cursr : Using updaterw() methd f updatable resulset Example: rs.updatestring( classname", yur enter class Name ); rs.updaterw(); Insert new rw t ResultSet: rs.mvetinsertrw(); //create new insert rw Call rs.updatexxx( fieldname,value) methds. Call rs.insertrw() ;//actual insert rw Call rs.mvetcurrentrw();//mve t previus rw. Delete the rw under the cursr: rs.deleterw(); CallableStatement Intrductin Advanced JDBC prgramming Part 3 A CallableStatement bject prvides a way t call stred prcedures in a standard way fr all RDBMSs. This call is written in an escape syntax that may take ne f tw frms: One frm with a result parameter. And the ther withut ne. Bth frms may have a variable number f parameters used fr input (IN parameters), utput (OUT parameters), r bth (INOUT parameters)

$CallableStatement Syntax fr calling stred prcedure CallableStatement IN parameters Syntax fr calling a stred prcedure in JDBC is: {call prcedure_name[(?,?$ preparecall("{call prcedurename(?,?)}"); Nte: The? placehlders are IN, OUT, r INOUT parameters depends n the stred prcedure prcedurename.

preparecall("{call prcedurename(?,?)}"); Nte: The? placehlders are IN, OUT, r INOUT parameters depends n the stred prcedure prcedurename.

9 CallableStatement Syntax fr calling stred prcedure CallableStatement IN parameters Syntax fr calling a stred prcedure in JDBC is: {call prcedure_name[(?,?,...)]} Stred prcedure that returns a result parameter is: {? = call prcedure_name[(?,?,...)]} Stred prcedure withut parameter: {call <prcedure_name>} Creating a CallableStatement Object : CallableStatement cstmt = cn.preparecall("{call prcedurename(?,?)}"); Nte: The? placehlders are IN, OUT, r INOUT parameters depends n the stred prcedure prcedurename. Passing in any IN parameter values t a CallableStatement bject is dne using the setxxx methds inherited frm PreparedStatement. The type f the value being passed in determines which setxxx methd t use. Fr example: CallableStatement cs=cn.preparecall ("{call myprc(?)}"); cs.setstring(1, cntt"); CallableStatement OUT parameters CallableStatement INOUT parameters If the stred prcedure returns OUT parameters, the JDBC type f each OUT parameter must be registered befre the CallableStatement bject can be executed. Registering the JDBC type is dne with the methd registeroutparameter. Then after the statement has been executed, CallableStatement's getxxx() methds can be used t retrieve OUT parameter values. A parameter that supplies input as well as accepts utput (an INOUT parameter) requires a call t the apprpriate setxxx methd (inherited frm PreparedStatement) in additin t a call t the methd registeroutparameter. The setxxx methd sets a parameter's value as an input parameter, and the methd registeroutparameter registers its JDBC type as an utput parameter

10 Transactin Intrductin Transactin Implementing transactin The majr reasn fr gruping cmmands int transactins is database integrity. If yu grup updates t a transactin, then the transactin either succeeds in its entirety and it can be cmmitted, r it fails smewhere in the middle. In that case, yu can carry ut a rllback and the database autmatically undes the effect f all updates that ccurred since the last cmmitted transactin. By default, a database cnnectin is in autcmmit mde, and each SQL cmmand is cmmitted t the database as sn as it is executed. Once a cmmand is cmmitted, yu cannt rll it back. T check the current autcmmit mde setting, call the getautcmmit() methd f the Cnnectin class. 1. Yu turn ff autcmmit mde with the cmmand: cnn.setautcmmit(false); 2. Nw yu create a statement bject in the nrmal way: Statement stat = cnn.createstatement(); 3. Call executeupdate any number f times. 4. When all cmmands have been executed, call the cmmit methd: cnn.cmmit(); 5. Hwever, if an errr ccurred, call : cnn.rllback(); Transactin Implementing transactin with batch update Fr prper errr handling in batch mde, yu want t treat the batch executin as a single transactin. If a batch fails in the middle, yu want t rll back t the state befre the beginning f the batch. Metadata JDBC can give yu additinal infrmatin abut the structure f a database and its tables. Fr example, yu can get a list f the tables in a particular database r the clumn names and types f a table In SQL, data that describes the database r ne f its parts is called metadata (t distinguish it frm the actual data that is stred in the database). Yu can get tw kinds f metadata: abut a database and abut a result set

11 Metadata Getting Infrmatin abut a Result Set When yu send a SELECT statement using JDBC, yu get back a ResultSet bject cntaining the data that satisfied yur criteria. Yu can get infrmatin abut this ResultSet bject by creating a ResultSetMetaData bject and invking ResultSetMetaData methds n it. Ex: Metadata Getting Infrmatin abut a Database r Database System Once yu have an pen cnnectin with a DBMS, yu can create a DatabaseMetaData bject that cntains infrmatin abut that database system. Using the Cnnectin bject cn, the fllwing line f cde creates the DatabaseMetaData bject dbmd: DatabaseMetaData dbmd = cn.getmetadata(); S yu can use it s methd t get all tables, stre prcedure, view, frm the database. Example Rw Sets The RwSet interface extends the ResultSet interface, but rw sets dn't have t be tied t a database cnnectin. The javax.sql.rwset package prvides the fllwing interfaces that extend the RwSet interface: CachedRwSet WebRwSet FilteredRwSet and JinRwSet JdbcRwSet 43 Rw Sets CachedRwSet (1) A CachedRwSet allws discnnected peratin. A cached rw set cntains all data frm a result set. Yu can clse the cnnectin and still use the rw set. Each user cmmand simply pens the database cnnectin, issues a query, puts the result in a rw set, and then clses the database cnnectin. Yu can mdify the data in a cached rw set. The mdificatins are nt immediately reflected in the database. Yu need t make an explicit request t accept the accumulated changes. The CachedRwSet recnnects t the database and issues SQL cmmands t write the accumulated changes

acceptchanges(cn); A rw set that cntains the result f a cmplex query will nt be able t write back changes t the database. Yu shuld be safe if yur rw set cntains data frm a single table.

12 Rw Sets CachedRwSet (2) Cached rw sets are nt apprpriate fr large query results. Yu can ppulate a CachedRwSet frm a result set: If yu mdified the rw set cntents, yu must write it back t the database by calling rwset.acceptchanges(cn); A rw set that cntains the result f a cmplex query will nt be able t write back changes t the database. Yu shuld be safe if yur rw set cntains data frm a single table. Rw Sets Other Rw sets A WebRwSet is a cached rw set that can be saved t an XML file. The XML file can be mved t anther tier f a web applicatin, where it is pened by anther WebRwSet bject. The FilteredRwSet and JinRwSet interfaces supprt lightweight peratins n rw sets that are equivalent t SQL SELECT and JOIN peratins. These peratins are carried ut n the data stred in rw sets, withut having t make a database cnnectin. A JdbcRwSet is a thin wrapper arund a ResultSet. It adds useful getters and setters frm the RwSet interface, turning a result set int a "bean." Summary FAQ Cnnect t database JDBC driver Manipulating with JDBC bject( Cnnectin, Statement, CallableStatement, ResultSet...) Scrllable and Updatable ResultSet Transactin Metadata Rw sets

13 That s all fr this sessin! Thank yu all fr yur attentin and patient! 49 13

Java Database Connectivity

Java Database Connectivity Advanced Java Prgramming Curse Java Database Cnnectivity By Võ Văn Hải Faculty f Infrmatin Technlgies Industrial University f H Chi Minh City Sessin bjectives JDBC basic Wrking with JDBC Advanced JDBC