Lesson 5 1. JNI, cont 2. JDBC 3. Intro to Graphics – Image Processing

Announcements  Homework due tonight midnight!  Between tonight and Thurs at midnight = 10% penalty  After Thurs midnight = no credit  New homework announced Wed. –Graphics + JDBC + JNI + RMI –two week deadline

JNI, cont.

JNI Arrays  Finish up reading Lesson4 JNI notes  Today, we will finish by discussing the most practical topic – arrays.  Multi-dimensional arrays are a complete headache! In java, these map to arrays of jobjects, which have to be accessed a row at a time.  Best to use 1d array even for multid type calculations!

Smoothing test  Consider algorithm to filter 1d data (see course examples).  We’ll compare the following: –pure java version –native version  We’ll do this on several different platforms and look at relative timings.

Issues with JNI arrays  Arrays in java mapped to opaque C types: –jintArray –jdoubleArray –jcharArray –jobejctArray –etc.  Best method to access elements Xxx* getXxxArrayElements(JNIEnv, jxxxArray,flag); Returns pointer to block of array elements But wait! this pointer may be a pointer to a copy!!

Releasing Arrays  To determine if it is a copy, the flag parameter is used (see example).  This is obviously crucial for performance – some jvm’s implement this way, others don’t.  We’ll see both examples today.  Finally, when finished use: releaseXxxArrayElements(Xxx*, jXxxArray, flag);

JDBC Using Java to issue SQL commands

Basic Database Concepts  When to use flat files vs. database? –Data is simple, static, volume is small, accessed by one process at a time on single system. –Cost of database software is prohibitive –Extremely high performance –Database is overkill

Databases  Built-in methods to source, access, search data.  Application independent of internal data representation – much lower maintenance costs.  Run in server mode, provides security.  Built-in support for transactions, concurrency, etc.

Relational Databases  Composed of tables each of which has rows and columns.  Each row or record represents an entity.  Each column or field represents an attribute.  Like an array of structures in C or Java.  Other concepts: primary key, compound key, artificial key, foreign key.

Object-Oriented Databases  Not clear exactly when a db officially becomes OO.  Provide direct support for managing objects and relationships among them – data + methods.  Gaining popularity but still far less common than relational counterpart.  Many SQL vendors support some object extensions.

SQL  Used to stand for “Structured Query Language”.  Standard language for conversing with relational databases.  Composed of three sub-languages: –Data Definition Language (DDL) –Data Control Language (DCL) –Data Manipulation Language (DML)

DDL  Lets you define and revise the structure of relational databases. Examples: Create Database name [options] Create Table name ( columname datatype, … )  Only simple datatypes supported.

DCL  Lets user specify data security and integrity mechanisms that safeguard data  Not very standardized – varies from vendor to vendor.

DML  Functionality for retrieving, manipulating, deleting, sorting, searching data. Examples just to get flavor: –Select * From table; –Select columns From tables [Where condition]; –Select ItemNo, Qty From InvoiceLine; –Insert Into InvoiceLine; (InvoiceNo, LineNo, CustomerNo) Values (101, 100, 10);

How to use SQL  Database vendor typically supplies GUI front-end for issuing SQL queries.  Also usually supplies a scripting front-end for issuing SQL commands. –Called Interactive SQL, good for developing and debugging queries –Of limited use because cannot share data with program variables.  From within a programming language –Embedded SQL

JDBC  Java’s version of Embedded SQL  Interface fully specified in the standard Java language (ie J2SE).  Independent of database vendor’s specific SQL implementation.  Vendor supplies middleware driver to convert JDBC calls to native db hooks.  Similar to Microsoft’s ODBC

Advantages to JDBC model  Application can fairly easily migrate from one DBMS to another. Almost no code needs to be rewritten.  Easy to use since db requests return easy-to- manipulate java objects, with simple methods, java exceptions, etc.

Disadvantages of JDBC  Slower  Cannot take advantage of all SQL extensions of a particular vendor (though it can take advantage of many).

Using JDBC on cluster  To use JDBC on the cs cluster, you’ll need to either install a database or use one of our dbase servers (mysql or sybase).  In this example I’ll show how to use the myql server.  First, you must register for a mysql account  After registering, try logging on and creating a few tables. You should have a database under your login name in which you can create the tables.

Using JDBC  Basic steps for connecting to dbase server 1.Load JDBC driver 2.Define the connection object 3.Establish the connection 4.Create the statement object 5.Execute a query or update with statement object 6.Process the returned ResultSet 7.Close the Connection

Loading the Driver  Each DBMS vendor must supply the driver class which converts JDBC calls to their own native db calls.  This needs to be loaded only once per application.  When loaded, its static initializer is called and the driver is registered with the DriverManager.  Best technique (assuming our sql driver) Class.forName(“org.gjt.mm.mysql.Driver”); –note: you’ll need a copy of mysql-connector-java stable-bin.jar in your classpath.

Define the Connection  Each vendor supplies info on what connection URL to use.  For mysql installed on cluster the following works: String conURL = “jdbc:mysql://dbserver/mydatabase”;

Establish the Connection  Issue the following command to create a single connection to the database java.sql.Connection conn = DriverManager.getConnection(URL);

Create a Statement Object  Once a connection object is obtained, you must use it to create a Statement. import java.sql.Statement; Statement st = conn.createStatement();

Execute Query  To execute standard SQL commands, you need to pass a valid SQL String to the executeQuery method of the statement object. A java object of type ResultSet is returned.  Import java.sql.ResultSet; String query = “SELECT * FROM table”; ResultSet res = st.executeQuery(query);

Process the Results  The ResultSet object is java’s representation of the data returned from the db query. The most typical way of manipulating the ResultSet is something like: While (res.next()) { System.out.println(res.getString(1) + “ “ + res.getString(2) + …);  Study the ResultSet API to see all of the ways in which the data can be accessed, modified, modified locally/globally, etc.

ResultSet in more detail  Like an Iterator or Enumerator.  However, must call next() once to move to first row.  Each call to next then moves to subsequent row.  For the current ResultSet row, there are two ways to access the values of the columns: –by String name Xxx getXxx(int columnNumber); –by column number (starting at 1) Xxx getXxx(String columName);

Execute update  To execute an update, pass appropriate SQL string to executeUpdate method: –e.g. st.executeUpdate(“UPDATE Books SET Price = Price – 5.00”);  Note that execute can be used for both updates and queries, though it is clearer to use one or the other.  executeUpdate returns count of rows modified by update procedure.

General observations  In executeXXX calls, SQL string need not end with any specific terminator st.execute(“Select * from TABLE”);  Statement objects can be reused for many queries – no need to create new one each time st.execute(blah1); st.execute(blah2);  Indicate nesting with altnerate single/double quotes stmt.executeUpdate( "INSERT INTO COFFEES " + "VALUES ('Colombian', 101, 7.99, 0, 0)"); dbms-specific terminator auto- matically added

General Observations, cont.  When using ResultSet object, Java will try to convert to requested type whenever possible. For example, rs.getString(...) is valid for any sql type, rs.getInt can also retrieve floats, etc.

 TINYINT: getByte (recommended) –Can also be read using getShort, getInt, getLong, getFloat, getDouble, getBigDecimal, getBoolean, getString, getObject  SMALLINT: getShort (recommended) –Can also be read using getByte, getInt, getLong, getFloat, getDouble, getBigDecimal, getBoolean, getString, getObject

 INTEGER: getInt (recommended) –Can also be read using getByte, getShort, getLong, getFloat, getDouble, getBigDecimal, getBoolean, getString, getObject  BIGINT: getLong (recommended) –Can also be read using getByte, getShort, getInt, getFloat, getDouble, getBigDecimal, getBoolean, getString, getObject

 REAL: getFloat (recommended) –Can also be read using getByte, getShort, getInt, getLong, getDouble, getBigDecimal, getBoolean, getString, getObject  FLOAT: getDouble (recommended) –Can also be read using getByte, getShort, getInt, getLong, getFloat, getBigDecimal, getBoolean, getString, getObject

 DOUBLE: getDouble (recommended) –Can also be read using getByte, getShort, getInt, getLong, getFloat, getBigDecimal, getBoolean, getString, getObject  DECIMAL: getBigDecimal (recommended) –Can also be read using getByte, getShort, getInt, getLong, getFloat, getDouble, getBoolean, getString, getObject  NUMERIC: getBigDecimal (recommended) –Can also be read using getByte, getShort, getInt, getLong, getFloat, getDouble, getBoolean, getString, getObject

 BIT: getBoolean (recommended) –Can also be read using getByte, getShort, getInt, getLong, getFloat, getDouble, getBigDecimal, getString, getObject  CHAR: getString (recommended) –Can also be read using getByte, getShort, getInt, getLong, getFloat, getDouble, getBigDecimal, getBoolean, getDate, getTime, getTimestamp, getAsciiStream, getUnicodeStream, getObject

 VARCHAR: getString (recommended) –Can also be read using getByte, getShort, getInt, getLong, getFloat, getDouble, getBigDecimal, getBoolean, getDate, getTime, getTimestamp, getAsciiStream, getUnicodeStream, getObject  LONGVARCHAR: getAsciiStream, getUnicodeStream (both recommended) –Can also be read using getByte, getShort, getInt, getLong, getFloat, getDouble, getBigDecimal, getBoolean, getString, getDate, getTime, getTimestamp, getObject  BINARY: getBytes (recommended) –Can also be read using getString, getAsciiStream, getUnicodeStream, getBinaryStream, getObject

 VARBINARY: getBytes (recommended) –Can also be read using getString, getAsciiStream, getUnicodeStream, getBinaryStream, getObject  LONGVARBINARY: getBinaryStream (recommended) –Can also be read using getString, getBytes, getAsciiStream, getUnicodeStream, getObject

 DATE: getDate (recommended) –Can also be read using getString, getTimestamp, getObject  TIME: getTime (recommended) –Can also be read using getString, getTimestamp, getObject  TIMESTAMP: getTimestamp (recommended) –Can also be read using getString, getDate, getTime, getObject

Version 2: Which types each ResultSet.getXXX method can read  getByte: TINYINT (recommended) –Can also read SMALLINT, INTEGER, BIGINT, REAL, FLOAT, DOUBLE, DECIMAL, NUMERIC, BIT, CHAR, VARCHAR, LONGVARCHAR

 getShort: SMALLINT (recommended) –Can also read TINYINT, INTEGER, BIGINT, REAL, FLOAT, DOUBLE, DECIMAL, NUMERIC, BIT, CHAR, VARCHAR, LONGVARCHAR  getInt: INTEGER (recommended) –Can also read TINYINT, SMALLINT, BIGINT, REAL, FLOAT, DOUBLE, DECIMAL, NUMERIC, BIT, CHAR, VARCHAR, LONGVARCHAR

 getLong: BIGINT (recommended) –Can also read TINYINT, SMALLINT, INTEGER, REAL, FLOAT, DOUBLE, DECIMAL, NUMERIC, BIT, CHAR, VARCHAR, LONGVARCHAR  getFloat: REAL (recommended) –Can also read TINYINT, SMALLINT, INTEGER, BIGINT, FLOAT, DOUBLE, DECIMAL, NUMERIC, BIT, CHAR, VARCHAR, LONGVARCHAR

 getDouble: FLOAT, DOUBLE (both recommended) –Can also read TINYINT, SMALLINT, INTEGER, BIGINT, REAL, DECIMAL, NUMERIC, BIT, CHAR, VARCHAR, LONGVARCHAR

 getBigDecimal: DECIMAL, NUMERIC (both recommended) –Can also read TINYINT, SMALLINT, INTEGER, BIGINT, REAL, FLOAT, DOUBLE, BIT, CHAR, VARCHAR, LONGVARCHAR  getBoolean: BIT (recommended) –Can also read TINYINT, SMALLINT, INTEGER, BIGINT, REAL, FLOAT, DOUBLE, DECIMAL, NUMERIC, CHAR, VARCHAR, LONGVARCHAR

 getString: CHAR, VARCHAR (both recommended) –Can also read TINYINT, SMALLINT, INTEGER, BIGINT, REAL, FLOAT, DOUBLE, DECIMAL, NUMERIC, BIT, LONGVARCHAR, BINARY, VARBINARY, LONGVARBINARY, DATE, TIME, TIMESTAMP  getBytes: BINARY, VARBINARY (both recommended) –Can also read LONGVARBINARY

 getDate: DATE (recommended) –Can also read CHAR, VARCHAR, LONGVARCHAR, TIMESTAMP  getTime: TIME (recommended) –Can also read CHAR, VARCHAR, LONGVARCHAR, TIMESTAMP  getTimestamp: TIMESTAMP (recommended) –Can also read CHAR, VARCHAR, LONGVARCHAR, DATE, TIME

 getAsciiStream: LONGVARCHAR (recommended) –Can also read CHAR, VARCHAR, BINARY, VARBINARY, LONGVARBINARY  getUnicodeStream: LONGVARCHAR (recommended) –Can also read CHAR, VARCHAR, BINARY, VARBINARY, LONGVARBINARY

 getBinaryStream: LONGVARBINARY (recommended) –Can also read BINARY, VARBINARY  getObject: (no recommended type) –Can read TINYINT, SMALLINT, INTEGER, BIGINT, REAL, FLOAT, DOUBLE, DECIMAL, NUMERIC, BIT, CHAR, VARCHAR, LONGVARCHAR, BINARY, VARBINARY, LONGVARBINARY, DATE, TIME, TIMESTAMP

Prepared Statements  A statement that is executed many times can be optimized by instead using a PreparedStatement  PreparedStatement objects are sent to the dbms for precompilation.  Example PreparedStatement updateSales = con.prepareStatement( "UPDATE COFFEES SET SALES = ? WHERE COF_NAME LIKE ?"); updateSales.setInt(1, 75); updateSales.setString(2, "Colombian"); updateSales.executeUpdate():

Transactions  Transactions are sequences of commands that are only executed if all commands in sequence successfully complete.  If the commands complete successfully, they are commited.  If any command fails, the commands are rolled back.  Fundamental to databases/SQL. How to do with JDBC?

Transactions with JDBC  By default, each command is independently execute and commit.  To change this, execute the following command on a connection object con:con.setAutoCommit(false); st.executeUpdate(command1); st.executeUpdate(command2); con.commit()/con.rollback();

Stored Procedures  To create, use executeUpdate with dbms-specific String to define stored procedure. Example: String createProcedure = "create procedure SHOW_SUPPLIERS " + "as " + "select SUPPLIERS.SUP_NAME, COFFEES.COF_NAME " + "from SUPPLIERS, COFFEES " + "where SUPPLIERS.SUP_ID = COFFEES.SUP_ID " + "order by SUP_NAME"; Statement stmt = con.createStatement(); stmt.executeUpdate(createProcedure);

Calling stored procedured  Stored procedures can be called using CallableStatement object. Example: CallableStatement cs = con.prepareCall("{call SHOW_SUPPLIERS}"); ResultSet rs = cs.executeQuery();  Notice the {} around the prepared statement call. This is required for java to translate into appropriate dbms- specific sql.

JDBC2.0 features  JDBC2.0 features are automatically available in any version of j2sdk >= 2.0  List of JDBC2.0 features –Scroll forward and backward in a result set or move to a specific row –Make updates to database tables using methods in the Java programming language instead of using SQL commands –Send multiple SQL statements to the database as a unit, or batch –Use the new SQL3 datatypes as column values

Scrollable result sets Statement stmt = con.createStatement( ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_READ_ONLY); Notice two new arguments. Possible values for first are as follows: arg1: TYPE_SCROLL_SENSITIVE: backward scrollable TYPE_SCROLL_INSENSITIVE: backward scrollable TYPE_FORWARD_ONLY (default): not backward scrollable arg2: CONCUR_READ_ONLY (default): cannot update directly CONCUR_UPDATABLE: can be used to udpate directly Focus on arg1 first: for first two types, new set of methods defined to navigate more easily through results.

Methods for scrollable ResultSets  Many new methods to navigate: –afterLast(); //position pointer after last row –previous(); //opposite of next() –absolute(i);//go to the i’th row –absolute(-i);//go to the i’th row from end –relative(i);//go i rows away from this point –getRow();/returns current row –isFirst(), isLast(), isBeforeFirst(), is AfterLast();/ boolean pos query functions

Updatable ResultSets  Can use Java methods to update table rather than sql strings.  Must create statements with CONCUR_UPDATABLE flag: Statement stmt = con.createStatement(ResultSet.TYPE_SCRO LL_SENSITIVE,ResultSet.CONCUR_UPDAT ABLE);

Updating a value  To update a value in a Table, use the updateXXX procedure. Example: stmt.executeUpdate("UPDATE COFFEES SET PRICE = 10.99" + "WHERE COF_NAME = FRENCH_ROAST_DECAF"); uprs.last(); //move to last row uprs.updateFloat("PRICE", 10.99); //change PRICE column to new value  Note that updateXXX works implictly on current row  Note that updateXXX can operate on col numbers as well as col names

Committing an updated value  After previous call to updateXXX, database is still not updated, only ResultSet is.  Must call updateRow() to complete operation with dbms.  call cancelRowUpdates() to cancel an update that you no longer wish to commit  Note that all row references refer to ResultSet object, which may differ from database table modulo updates!

Inserting rows  Also can insert values directly in Java.  Must move cursor to special row called insert row and then call insert method. uprs.moveToInsertRow(); uprs.updateString("COF_NAME", "Kona"); uprs.updateInt("SUP_ID", 150); uprs.updateFloat("PRICE", 10.99); uprs.updateInt("SALES", 0); uprs.updateInt("TOTAL", 0); uprs.insertRow(); updates both dbase and ResultSet at same time

Deleting rows  Simply call deleteRow() on current row

Seeing Changed ResultSets  Always visible to others once you close and reopen (or new query executed).  May or may not be visible to others while ResultSet still open. Depends on: –dbms –driver –flags used in creating ResultSet TypeScrollSensitive  see all updates, might or might not see inserts/deletes Need to use metadata methods to be sure

MetaData methods  Provide user with rich array of info about database itself, tables, etc.  java.sql.DatabaseMetaData –info about database as a whole. version, features supported, vendor, etc.  java.sql.ResultSetMetaData –data about specific ResultSet – names of columns, size of types, types of data, etc.  Study API for more details

Java/SQL datatype mapping SQL data typeJava data type INTEGERint SMALLINTshort NUMERIC(m,n)java.sql.Numeric FLOAT(n)double REALfloat DOUBLEdouble CHARACTER(n)String VARCHAR(n)String

Java/SQL datatype mapping BOOLEANboolean DATEjava.sql.Date TIMEjava.sql.Time TIMESTAMPjava.sql.Timestamp BLOBjava.sql.Blob CLOBjava.sql.Clob ARRAYjava.sql.Array

Other methods of interest  java.sql.Statement –void cancel(); Aysnchronously cancels an executing SQL request.  java.sql.ResultSet –int findColumn(String columName); gives the column index for column columName -void close(); closes the current result set.

SQLException methods  java.sql.SQLException –String getSQLState(); –int getErrorCode() gets the vendor-specific exception code –SQLException getNextException(); gets the Exception chained to this one for more specific information

Introduction to awt Graphics Reading, displaying images

Awt Image processing  Java has recently added many classes for simplifying image manipulation.  We’ll start by looking at some of these in the context of howto’s for simple things –reading a jpg, gif, etc. from a file –displaying jpg, gif, etc. to a graphics window –constructing an image from raw pixels –manipulating individual pixesl of an image –writing an image to a file (see course examples)

Reading an image  Easiest way to read an image file. Use static read method in javax.image.ImageIO class: BufferedImage img = ImageIO.read(new File(“name”));  Note that “name” can be name of one of many standard Image file formats.

Writing an image  Writing an image is as easy as reading it. Simple use the ImageIO.write method: BufferedImage image; ImageIO.write(new File(name), “gif”,image);  List of supported output file types is can be obtain from: –String[] ImageIO.getWriterFormatNames();

Manipulating image bytes  It is possible to set/access each image pixel independently: image = new BufferedImage(w,h,BufferedImage.TYPE_INT_ARGB); WritableRaster raster = image.getRaster(); raster.setPixel(ival,jval,{rval,gval,bval,alphval}); or int pixel[4]; raster.getPixel(ival,jval,pixel);

Transforming images  It is also possible to transform images without accessing pixels using classes that implement the ImageOp interface.  See ImageProcessor.java example