Servlets Chapter 9 database connectivity. Servlets and db Messaging, storefronts and search engines...

Servlets Chapter 9

database connectivity

Servlets and db

• Messaging, storefronts and search engines all require databases.

• Such sites may be complicated to build and have performance issues.

• We will use SQL and JDBC.

• The JDBC and servlet API are a good solution to db issues.

lifecycle

• The servlet lifecycle allows servlets to maintain pools of connections to a database.

• Additionally, as per Chapter 3, servlets run in the jvm and have low server load. Once loaded the server thread may remain in the server until it is shutdown.

Platform independence

• Servlets written for oracle can easily be modified for sybase, mysql or odbc.

• Text does many connection types. I only do mysql.

Connectors

• Connecting to mysql from java requires a connector.

• Applications and servlets can connect to the db.

• MYSQL listens on port 3306• You’ll have to go to the mysql site to

download mysql-connector-java .zip• Unzip, and put the jar file in your

classpath.

Getting connections

• Imports:import java.sql.*;

• The first step in using a JDBC driver to get a db connection in your application involves loading the specific driver class into the application’s jvm.

• One way to do it is to use the Class.forName() method:Class.forName(“sun.jdbc.odbc.JdbcOdbcDriver”);• Once loaded, the driver registers itself with the

java.sql.DriverManager class as an available db driver.• Next step is to ask the driver manager to open a

connection to a given db specified in a URL. The method used is DriverManager.getConnection():

Connection con= DriverManager.getConnection(“jdbc etc”,”user”,”pw”);

MYSQL admin

administration

• Some slides show the mysqlcc (control center) but since we already have apache/php it is easier to continue to use PHPMyAdmin.

• You’ll need apache running to administer mysql using phpmyadmin.

• If Apache and Tomcat run on the same port you’ll have a problem.

• By default, apache is at 80 and tomcat is at 8080 but if you’ve changed those settings you might have trouble.

MYSQL admin and MYSQLcontrol center

• Download and install mysql.• Run MYSQL from the admintool (icon): • A little traffic light icon with a red light will appear lower

right monitor screen. • Rt-click this and select NT. (Selecting showme will open

the mysql admin GUI)• First, shutdown the service, then start the service

standalone.• The traffic light should be green indicating that mysql is

running.• MySQLMyAdmin is a good GUI for managing your db

MySQLCC

Some remarks

• Looking at user admin in the control center you can add users or set pws. (rt click user admin selection)

• Security is less tight for the “test” db, so that is where my examples are.

Add user

New user bob

A new table: rt click tables selection in mysql control center

Saving table/viewing table fields

Open table/query/insert record

• Under query type insert record to put some data in

The phonelookup servletimport java.io.*;import java.sql.*;import javax.servlet.*;import javax.servlet.http.*;public class DBPhoneLookup extends HttpServlet { public void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException { Connection con = null; Statement stmt = null; ResultSet rs = null; res.setContentType("text/html"); PrintWriter out = res.getWriter(); try { // Load (and therefore register) the Oracle Driver Class.forName("org.gjt.mm.mysql.Driver"); // Get a Connection to the database con = DriverManager.getConnection( "jdbc:mysql://localhost/test", "bob", "justabob");//or user= “root”, pw=”” // Create a Statement object stmt = con.createStatement(); // Execute an SQL query, get a ResultSet rs = stmt.executeQuery("SELECT NAME, EMAIL FROM guestlist");//added cmt and id to this // Display the result set as a list out.println("<HTML><HEAD><TITLE>Phonebook</TITLE></HEAD>"); out.println("<BODY>"); out.println("<UL>"); while(rs.next()) { out.println("<LI>" + rs.getString("name") + " " + rs.getString("email")); }//actually added more to get all columns out.println("</UL>"); out.println("</BODY></HTML>"); } catch(ClassNotFoundException e) { out.println("Couldn't load database driver: " + e.getMessage()); } catch(SQLException e) { out.println("SQLException caught: " + e.getMessage()); } finally { // Always close the database connection. try { if (con != null) con.close(); } catch (SQLException ignored) { } } }}

Phone lookup (using guestbook table)

phonebook

• This is about as simple as it could be.

• It does not establish a pool of connections – it just opens one.

• It does not get db driver and user/pw from servlet context or init params. These are hardcoded.

HtmlSQL result class presents query result as an html table

public class HtmlSQLResult { private String sql; private Connection con;

public HtmlSQLResult(String sql, Connection con) { this.sql = sql; this.con = con; }

public String toString() { // can be called at most once StringBuffer out = new StringBuffer();

// Uncomment the following line to display the SQL command at start of table // out.append("Results of SQL Statement: " + sql + "<P>\n");

try { Statement stmt = con.createStatement();

if (stmt.execute(sql)) { // There's a ResultSet to be had ResultSet rs = stmt.getResultSet(); out.append("<TABLE>\n");

ResultSetMetaData rsmd = rs.getMetaData();

int numcols = rsmd.getColumnCount();

continued// Title the table with the result set's column labels out.append("<TR>"); for (int i = 1; i <= numcols; i++) out.append("<TH>" + rsmd.getColumnLabel(i)); out.append("</TR>\n");

while(rs.next()) { out.append("<TR>"); // start a new row for(int i = 1; i <= numcols; i++) { out.append("<TD>"); // start a new data element Object obj = rs.getObject(i); if (obj != null) out.append(obj.toString()); else out.append(" "); } out.append("</TR>\n"); }

// End the table out.append("</TABLE>\n"); } else { // There's a count to be had out.append("<B>Records Affected:</B> " + stmt.getUpdateCount()); } } catch (SQLException e) { out.append("</TABLE><H1>ERROR:</H1> " + e.getMessage()); }

return out.toString(); }}

Reuse example

• can reuse connection created in advance in init method

Here are just the parts that differ from previous phonebook example

public void init() throws ServletException { try { // Load (and therefore register) the Oracle Driver

Class.forName("org.gjt.mm.mysql.Driver"); // Get a Connection to the database con = DriverManager.getConnection( "jdbc:mysql://localhost/test", "bob", "justabob"); }

catch (ClassNotFoundException e) { throw new UnavailableException("Couldn't load database driver"); } catch (SQLException e) { throw new UnavailableException("Couldn't get db connection"); } } public void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException { res.setContentType("text/html"); PrintWriter out = res.getWriter();

out.println("<HTML><HEAD><TITLE>Phonebook</TITLE></HEAD>"); out.println("<BODY>"); HtmlSQLResult result = new HtmlSQLResult("SELECT NAME, EMAIL, CMT, ID FROM guestlist", con);

Adding a guest to our guestlist: the get methods calls post… this mimicks text example

“OrderHandler”

• I didn’t change the message text servlet printed out• uses connection pool class

Phone lookup checks the table to verify guest added

add a guest servletpublic class AddAGuestPool extends HttpServlet { private ConnectionPool pool; public void init() throws ServletException { try { pool = new ConnectionPool("org.gjt.mm.mysql.Driver","jdbc:mysql://localhost/test", "bob", "justabob",5); }//get

connections catch (Exception e) { throw new UnavailableException("Couldn't create connection pool"); } }public void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {doPost(req,res);} public void doPost(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException { Connection con = null; res.setContentType("text/plain"); PrintWriter out = res.getWriter(); try { con = pool.getConnection(); // Turn on transactions con.setAutoCommit(false); Statement stmt = con.createStatement(); stmt.executeUpdate("INSERT INTO guestlist(NAME,ID,EMAIL,CMT)values ('Xavier Poindexter

III','81234','[email protected]','astounding salad bar')");//this would be form data con.commit(); out.println("Order successful! Thanks for your business!"); } catch (Exception e) { // Any error is grounds for rollback try {con.rollback(); } catch (Exception ignored) { } out.println("Order failed. Please contact technical support."); } finally { if (con != null) pool.returnConnection(con); } }}

Connectionpool servlet in slide notes.

• Blackscreen output (server screen) provides some information

Guestbook servlet revisited: form posts data to db…entire servlet in slide notes

Guestbook servlet revisited after pressing button (code in notes)

Guestbook servlet: some notes• Init gets a pool of connections:public void init() throws ServletException { try { ServletContext context = getServletContext(); synchronized (context) { // A pool may already be saved as a context attribute pool = (ConnectionPool) context.getAttribute("pool"); if (pool == null) { // Construct a pool using our context init parameters // connection.driver, connection.url, user, password, etc pool = new ConnectionPool(new ContextProperties(context), 3); context.setAttribute("pool", pool); } } } catch (Exception e) { throw new UnavailableException( "Failed to fetch a connection pool from the context: " + e.getMessage()); } }

Guestbook servlet: some notes• doGet and doPost are a series of method calls:public void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException { res.setContentType("text/html"); PrintWriter out = res.getWriter();

printHeader(out); printForm(out); printMessages(out); printFooter(out); }

// Add a new entry, then dispatch back to doGet() public void doPost(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException { handleForm(req, res); doGet(req, res); }

Guestbook servlet: some notes• Printing a form:private void printForm(PrintWriter out) { out.println("<FORM METHOD=POST>"); // posts to itself out.println("<B>Please submit your feedback:</B><BR>"); out.println("Your name: <INPUT TYPE=TEXT

NAME=name><BR>"); out.println("Your email: <INPUT TYPE=TEXT

NAME=email><BR>"); out.println("Comment: <INPUT TYPE=TEXT SIZE=50

NAME=comment><BR>"); out.println("<INPUT TYPE=SUBMIT VALUE=\"Send

Feedback\"><BR>"); out.println("</FORM>"); out.println("<HR>"); }

HandleForm is insert record function

private void handleForm(HttpServletRequest req, HttpServletResponse res) throws ServletException { String name = req.getParameter("name"); String email = req.getParameter("email"); String comment = req.getParameter("comment"); Connection con = null; PreparedStatement pstmt = null; try { con = pool.getConnection(); // Use a prepared statement for automatic string escaping pstmt = con.prepareStatement(INSERT); long time = System.currentTimeMillis(); pstmt.setString(1, Long.toString(time)); pstmt.setString(2, name); pstmt.setString(3, email); pstmt.setString(4, comment); pstmt.executeUpdate(); } catch (SQLException e) { throw new ServletException(e); } finally { try { if (pstmt != null) pstmt.close(); } catch (SQLException ignored) { } pool.returnConnection(con); }

// Make note we have a new last modified time lastModified = System.currentTimeMillis(); }

printMessages method provides Read functionality

private void printMessages(PrintWriter out) throws ServletException { String name, email, comment; Connection con = null; Statement stmt = null; ResultSet rs = null; try { con = pool.getConnection(); stmt = con.createStatement(); rs = stmt.executeQuery(SELECT_ALL); while (rs.next()) { name = rs.getString(1); if (rs.wasNull() || name.length() == 0) name = "Unknown user"; email = rs.getString(2); if (rs.wasNull() || email.length() == 0) name = "Unknown email"; comment = rs.getString(3); if (rs.wasNull() || comment.length() == 0) name = "No comment"; out.println("<DL>"); out.println("<DT><B>" + name + "</B> (" + email + ") says"); out.println("<DD><PRE>" + comment + "</PRE>"); out.println("</DL>"); } } catch (SQLException e) { throw new ServletException(e); } finally { try { if (stmt != null) stmt.close(); } catch (SQLException ignored) { } pool.returnConnection(con); } }

doGet/doPost

• Updates, inserts and delets should call doPost method

• Select (read) should call doGet

Deleting a record… entire servlet in notes

…omitted imports and init which makes connection//Process the HTTP Post request public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html"); PrintWriter out = new PrintWriter (response.getOutputStream()); Statement stmt=null; String query=""; out.println("<html>"); out.println("<head><title>Servlet</title></head>"); out.println("<body>");try { stmt = con.createStatement (); String name = request.getParameter("name"); query="DELETE from table1 where name='" + name+"'"; out.println("Query: "+query+"<BR>"); int count=stmt.executeUpdate( query ); out.println("modified records ="+count); }catch (SQLException e2) { System.out.println("SQLException: "+e2); }finally{ out.println("</body></html>"); out.close();} }

Deleting a record…continued

//Process the HTTP Get request public void doGet(HttpServletRequest request, HttpServletResponse

response) throws ServletException, IOException { PrintWriter out = new PrintWriter (response.getOutputStream()); out.println("<html>"); out.println("<head><title>Servlet</title></head>"); out.println("<body>"); out.println("servlet does not support get"); out.println("</body></html>"); out.close(); }}

Context parameters in web.xml for guestbook connection

 <context-param> <param-name> connection.driver </param-name> <param-value> org.gjt.mm.mysql.Driver </param-value> </context-param> <context-param> <param-name> connection.url </param-name> <param-value> jdbc:mysql://localhost/test </param-value> </context-param><context-param> <param-name> user </param-name> <param-value> bob </param-value> </context-param> <context-param> <param-name> password </param-name> <param-value> justabob </param-value> </context-param>

Using session to hold connection information

Using session to hold connection information

• Code in next 3 slides is from a single file, shown in text examples 9-10 and 9-11

• I changed text redirect to go to my phonebook which lists a mysql table as html table

• The SessionBinderListener class (called ConnectionHolder) saves a single connection associated with each session.

• No changes are needed to ConnectionHolder text code

Using session to hold connection informationimport java.io.*;import java.sql.*;import javax.servlet.*;import javax.servlet.http.*;class ConnectionHolder implements HttpSessionBindingListener { private Connection con = null; public ConnectionHolder(Connection con) { // Save the Connection this.con = con; try { con.setAutoCommit(false); // transactions can extend between web pages! } catch(SQLException e) { // Perform error handling } } public Connection getConnection() { return con; // return the cargo } public void valueBound(HttpSessionBindingEvent event) { // Do nothing when added to a Session } public void valueUnbound(HttpSessionBindingEvent event) { // Roll back changes when removed from a Session // (or when the Session expires) try { if (con != null) { con.rollback(); // abandon any uncomitted data con.close(); } } catch (SQLException e) { // Report it } }}

Using session to hold connection Servletpublic class ConnectionPerClient extends HttpServlet { public void init() throws ServletException { try { Class.forName("org.gjt.mm.mysql.Driver");//note this is MySQL not oracle driver } catch (ClassNotFoundException e) { throw new UnavailableException("Couldn't load OracleDriver"); } } public void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException { res.setContentType("text/plain"); PrintWriter out = res.getWriter();

HttpSession session = req.getSession(true); Connection con; // Synchronize: Without this two holders might be created for one client synchronized (session) { // Try getting the connection holder for this client ConnectionHolder holder = (ConnectionHolder) session.getAttribute("servletapp.connection"); // Create (and store) a new connection and holder if necessary if (holder == null) { try { holder = new ConnectionHolder(DriverManager.getConnection("jdbc:mysql://localhost/test", "bob", "justabob"));//note…this is my db and my table and my user/pw info session.setAttribute("servletapp.connection", holder); } catch (SQLException e) { log("Couldn't get db connection", e); } }

Using session to hold connection Servlet// Get the actual connection from the holder con = holder.getConnection(); } // Now use the connection try { Statement stmt = con.createStatement();

stmt.executeUpdate("INSERT INTO guestlist(NAME,ID,EMAIL,CMT)values ('Didier B. Applebottom','993','[email protected]','Zappa lives!')");

//note..you need to run from a form, not hardcode entry // Charge the credit card and commit the transaction in another servlet res.sendRedirect(res.encodeRedirectURL( req.getContextPath() +

“DBPhoneLookup")); //note redirect change } catch (Exception e) { // Any error is grounds for rollback try { con.rollback(); session.removeAttribute("servletapp.connection"); } catch (Exception ignored) { } out.println("Order failed. Please contact technical support."); } }}

Remarks on the next set of slides

• These use a 3rd party connection broker class from javaexchange

• Require a dat file to be in tomcat/bin

• Require various package hierarchy (which I didn’t use) but see last sequence of slides for more remarks & examples.

Running Servlet2 from Tomcat

What you’ll need to do

• Move the broker class and servlet2 class files into your webapp/web-inf/classes directory. (I created a new webapp called database).

• The broker needs some other directories/files which came in the zip collection. These are in the org and com directories, specifically HttpServletJXGB imports:

import com.javaexchange.dbConnectionBroker.*;import org.gjt.mm.mysql.*;I copied these two directory structures into my

database/WEB_INF/classes directory

You need a new web.xml for this webapp. <web-app xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd" version="2.4">

 <display-name> servlet database connections </display-name>

<description> This is the Web application in which we work on database connections </description>

Web.xml continued  <servlet> <servlet-name>Servlet2</servlet-name> <description> A simple servlet opens a mysql connectionn and displays contents of a table </description> <servlet-class> Servlet2 </servlet-class> </servlet> <servlet> <servlet-name>HttpServletJXGB</servlet-name> <description> broker to database </description> <servlet-class> HttpServletJXGB </servlet-class> </servlet>  <servlet-mapping> <servlet-name>HttpServletJXGB</servlet-name> <url-pattern>/HttpServletJXGB</url-pattern> </servlet-mapping> <servlet-mapping> <servlet-name>Servlet2</servlet-name> <url-pattern>/Servlet2</url-pattern> </servlet-mapping></web-app>

Generating an html table

Uses HtmlSQLResult class from text

import java.sql.*;

public class HtmlSQLResult { private String sql; private Connection con;

public HtmlSQLResult(String sql, Connection con) { this.sql = sql; this.con = con; }

public String toString() { // can be called at most once StringBuffer out = new StringBuffer();

// Uncomment the following line to display the SQL command at start of table // out.append("Results of SQL Statement: " + sql + "<P>\n");

HtmlSQLResult from text, slide 2try { Statement stmt = con.createStatement(); if (stmt.execute(sql)) { // There's a ResultSet to be had ResultSet rs = stmt.getResultSet(); out.append("<TABLE>\n"); ResultSetMetaData rsmd = rs.getMetaData(); int numcols = rsmd.getColumnCount(); // Title the table with the result set's column labels out.append("<TR>"); for (int i = 1; i <= numcols; i++) out.append("<TH>" + rsmd.getColumnLabel(i)); out.append("</TR>\n"); while(rs.next()) { out.append("<TR>"); // start a new row for(int i = 1; i <= numcols; i++) { out.append("<TD>"); // start a new data element Object obj = rs.getObject(i); if (obj != null) out.append(obj.toString()); else out.append(" "); } out.append("</TR>\n"); }

HtmlSQLResult slide 3// End the table out.append("</TABLE>\n"); } else { // There's a count to be had out.append("<B>Records Affected:</B> " + stmt.getUpdateCount()); } } catch (SQLException e) { out.append("</TABLE><H1>ERROR:</H1> " + e.getMessage()); }


modifying servlet 2 doGet() public void doGet(HttpServletRequest request, HttpServletResponse

response) throws ServletException, IOException { response.setContentType("text/html"); PrintWriter out = new PrintWriter (response.getOutputStream()); Connection conn=myBroker.getConnection(); Statement stmt=null; String query; out.println("<html>"); out.println("<head><title>Servlet1</title></head>"); out.println("<body>"); //out.println("Hello World...Servlet2 is running!<BR>"); query="select * from table1";

hsr=new HtmlSQLResult(query,conn); String htmltable=hsr.toString();//can call just once myBroker.freeConnection(conn); // Release connection back to

pool out.println(htmltable); out.println(); out.close(); }

Deleting a record

Mike was deleted

doGet method of DeleteRec servlet public void doGet(HttpServletRequest request, HttpServletResponse response) throws

ServletException, IOException { response.setContentType("text/html"); PrintWriter out = new PrintWriter (response.getOutputStream()); Connection conn=myBroker.getConnection(); Statement stmt=null; String query=""; out.println("<html>"); out.println("<head><title>Servlet1</title></head>"); out.println("<body>"); //out.println("Hello World...Servlet2 is running!<BR>"); try { stmt = conn.createStatement (); query="DELETE from table1 where age=20"; out.println("Query: "+query+"<BR>"); int count=stmt.executeUpdate( query );

out.println("modified records ="+count); }catch (SQLException e2) { System.out.println("SQLException: "+e2); }finally { try{if(stmt != null) {stmt.close();}} catch(SQLException e1){System.out.println("SQLException:

"+e1);} myBroker.freeConnection(conn); // Release connection back to pool } out.println("</body></html>"); out.close();

Add a record

AddRec uses preparedStatement class public void doGet(HttpServletRequest request, HttpServletResponse response) throws

ServletException, IOException { response.setContentType("text/html"); PrintWriter out = new PrintWriter (response.getOutputStream()); Connection conn=myBroker.getConnection(); Statement stmt=null; String query=""; out.println("<html>"); out.println("<head><title>Servlet1</title></head>"); out.println("<body>");try { PreparedStatement pstmt=conn.prepareStatement("insert into table1

(name,grade,age) values (?,?,?)"); pstmt.clearParameters(); pstmt.setString(1,"Godzilla");//would be form params pstmt.setDouble(2,1.0); pstmt.setInt(3,123); pstmt.executeUpdate( ); }catch (SQLException e2) { System.out.println("SQLException: "+e2);}finally { try{if(stmt != null) {stmt.close();}} catch(SQLException e1){System.out.println("SQLException: "+e1);} myBroker.freeConnection(conn); } out.println("</body></html>"); out.close(); }

Same business, using html form

Servlet output

Display table using servlet

The form…really should use post

<FORM Method=GET Action="http://csci345.oneonta.edu:8080/database/AddARecordServlet">

name <input type=text name="name"><p>

age <input type=text name="age"><p>

grade <input type=text name="grade"><p><input type =submit></form>

Changes to addrecString name = request.getParameter("name"); String sage = request.getParameter("age"); String sgrade = request.getParameter("grade"); int age=Integer.parseInt(sage); double grade=Double.parseDouble(sgrade); out.println("adding"+name+","+grade+","+age); try { PreparedStatement pstmt=conn.prepareStatement("insert into table1

(name,grade,age) values (?,?,?)"); pstmt.clearParameters(); pstmt.setString(1,name); pstmt.setDouble(2,grade); pstmt.setInt(3,age);

pstmt.executeUpdate( );

Servlets and mysql

The next set of slides redo the last set but start with java files from

javaexchange.

Setting up the connectors

• The java connectors are in a subdirectory of mysql

• The html/pdf/etc documentation is in the docs subdirectory of this

You shouldn’t have to change classpath settings

• If you are developing servlets and/or JSPs, and your application server is J2EE-compliant, you should put the driver's .jar file in the WEB-INF/lib subdirectory of your webapp, as this is the standard location for third party class libraries in J2EE web applications.

• (note – if you don’t already have one, the lib directory is in web-inf at the same level as classes)

New driver class in j-connectors is com.mysql.Driver

Class.forName("com.mysql.Driver").newInstance(); //thentry {

Connection C = DriverManager.getConnection("jdbc:mysql://mysql.yourdomainname/database_com_au?user=user_name&password=password"); [use this code for MySQL]}catch (SQLException E) {System.out.println("SQLException: " + E.getMessage());System.out.println("SQLState: " + E.getSQLState());System.out.println("VendorError: " + E.getErrorCode());}

• The various MysqlDataSource classes support the following parameters (through standard "setter" methods):

• user• password• serverName (see the previous section

about fail-over hosts)• databaseName• port

The DriverManager needs to be told which JDBC drivers it should try to make Connections with

• The easiest way to do this is to use Class.forName() on the class that implements the java.sql.Driver interface. With MySQL Connector/J, the name of this class is com.mysql.jdbc.Driver. With this method, you could use an external configuration file to supply the driver class name and driver parameters to use when connecting to a database.

• Example 3.1. Registering the Driver With the DriverManager

• The following section of Java code shows how you might register MySQL Connector/J from the main() method of your application.

example

import java.sql.Connection; import java.sql.DriverManager; import java.sql.SQLException; ... try { Connection conn =

DriverManager.getConnection("jdbc:mysql://localhost/test?user=monty&password=greatsqldb");

// Do something with the Connection .... } catch (SQLException ex) { // handle any errors

System.out.println("SQLException: " + ex.getMessage()); System.out.println("SQLState: " + ex.getSQLState()); System.out.println("VendorError: " + ex.getErrorCode()); }

Opening a Connection to MySQL

• 3.1.2. Opening a Connection to MySQL• After the driver has been registered with the

DriverManager, you can obtain a Connection instance that is connected to a particular database by calling DriverManager.getConnection():

• Example 3.2. Obtaining a Connection From the DriverManager

• This example shows how you can obtain a Connection instance from the DriverManager. There are a few different signatures for the getConnection() method. You should see the API documentation that comes with your JDK for more specific information on how to use them.

The connectionimport java.sql.Connection; import java.sql.DriverManager; import java.sql.SQLException; ... try { ConnectionDriverManager.getConnection("jdbc:mysql://localhost/test?user=bob&password=xyz"); // Do something with the Connection .... } catch (SQLException ex) { // handle any errors System.out.println("SQLException: " + ex.getMessage()); System.out.println("SQLState: " + ex.getSQLState()); System.out.println("VendorError: " + ex.getErrorCode()); }

• Once a Connection is established, it can be used to create Statements and PreparedStatements, as well as retrieve metadata about the database. This is explained in the following sections.

A DBBroker class

• http://www.purpletech.com/code/

• Link has source for a db connector class in java to handle servlet to mysql connections.

http://www.purpletech.com/code/

public class HttpServletJXGB extends HttpServlet

• In notes

DbConnectionBroker in notes

• Is pretty big…like 500 lines

Using dbconnectionbroker in servletsclasses

com

javaexchange

DbConnectionBroker

DbConnectionBroker(java)

HttpServletJXB

oreilly

etc

JXGBConfig.dat needs to be in Tomcat bin or have path set carefully

dbDriver=org.gjt.mm.mysql.DriverdbServer=jdbc:mysql://localhost/testdbLogin=dbPassword=minConns=1maxConns=20logFileString=p:\\classes\\connections.logmaxConnTime=2

My addrec servlet

My addrec servlet I extended HttpServlet, not HttpJXBServlet so I put this in init:

public void init(ServletConfig config) throws ServletException { super.init(config); if(myBroker == null) { // Only created by first servlet to call

Properties p = new Properties(); try {

p.load(new FileInputStream("JXGBconfig.dat"));

String dbDriver = (String) p.get("dbDriver");String dbServer = (String) p.get("dbServer");String dbLogin = (String) p.get("dbLogin");String dbPassword = (String) p.get("dbPassword");int minConns = Integer.parseInt((String) p.get("minConns"));int maxConns = Integer.parseInt((String) p.get("maxConns"));String logFileString = (String) p.get("logFileString");status=status+dbDriver+dbServer+dbLogin+dbPassword+minConns+maxConns;double maxConnTime = (new Double((String)p.get("maxConnTime"))).doubleValue();

myBroker = new DbConnectionBroker(dbDriver,dbServer,dbLogin,dbPassword,

minConns,maxConns,logFileString,maxConnTime); status="connected";

} catch (FileNotFoundException f) {status="file not found";}

catch (IOException e) {status="other io prob";} }//if broker null}//init

doGet public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException

{ response.setContentType("text/html"); PrintWriter out = new PrintWriter (response.getOutputStream()); out.println("<html>"); out.println("<head><title>Servlet1</title></head>"); out.println("<body>"); out.println(status); Connection conn=myBroker.getConnection(); Statement stmt=null; String query=""; out.println("Hello World...addrec is running!<BR>"); try { PreparedStatement pstmt=conn.prepareStatement("insert into table1 (name,grade,age) values (?,?,?)"); pstmt.clearParameters(); pstmt.setString(1,"XXXXXXX");//////adding this item pstmt.setDouble(2,1.0); pstmt.setInt(3,123); pstmt.executeUpdate( ); }catch (SQLException e2) { System.out.println("SQLException: "+e2); }finally { try{if(stmt != null) {stmt.close();}} catch(SQLException e1){System.out.println("SQLException: "+e1);} myBroker.freeConnection(conn); // Release connection back to pool } out.println("</body></html>"); out.close();

}

In MySQLcontrol center, you can see record was successfully added

Generating an HTML table from a db table

DBTable servletpublic class DBTable extends HttpServlet{protected static DbConnectionBroker myBroker;private HtmlSQLResult hsr; //same code for init() as in AddRec servlet //Process the HTTP Get request public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException,

IOException { response.setContentType("text/html"); PrintWriter out = new PrintWriter (response.getOutputStream()); Connection conn=myBroker.getConnection(); Statement stmt=null; String query;

out.println("<html>"); out.println("<head><title>Servlet1</title></head>"); out.println("<body>"); //out.println("Hello World...Servlet2 is running!<BR>"); query="select * from table1";

hsr=new HtmlSQLResult(query,conn); String htmltable=hsr.toString();//can call just once myBroker.freeConnection(conn); // Release connection back to pool out.println(htmltable); out.println(); out.close(); } //Process the HTTP Post request public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException,

IOException { } public String getServletInfo() { return "DBTable"; }

code to generate html table from query resultsetimport java.sql.*;public class HtmlResultSet { private ResultSet rs; public HtmlResultSet(ResultSet rs) { this.rs = rs; } public String toString() { // can be called at most once StringBuffer out = new StringBuffer(); // Start a table to display the result set out.append("<TABLE>\n"); try { ResultSetMetaData rsmd = rs.getMetaData(); int numcols = rsmd.getColumnCount();

// Title the table with the result set's column labels out.append("<TR>"); for (int i = 1; i <= numcols; i++) { out.append("<TH>" + rsmd.getColumnLabel(i)); } out.append("</TR>\n"); while(rs.next()) { out.append("<TR>"); // start a new row for (int i = 1; i <= numcols; i++) { out.append("<TD>"); // start a new data element Object obj = rs.getObject(i); if (obj != null) out.append(obj.toString()); else out.append(" "); } out.append("</TR>\n"); } // End the table out.append("</TABLE>\n"); } catch (SQLException e) { out.append("</TABLE><H1>ERROR:</H1> " + e.getMessage() + "\n"); }


Servlet communication to accomplish a goal

• It makes sense for a single servlet to do the db connection and query.

• A front end servlet might collect information to form a query, send the query to this db servlet and display the result.

• The session is one place where the information (query string and result set) can be placed.

• Servlet include is one mechanism to get two servlets to work together.

An html to collect a query and the results of two servlets collaborating

IncludeServlet

• collects query from html form

• puts it in the session

• performs a dispatcher include to the DBLookup servlet (to keep control of the session)

• Looks in the session for the resultset

• Displays results as it likes

IncludeServletpublic void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException { res.setContentType("text/html"); PrintWriter out = res.getWriter(); String[] queries =req.getParameterValues("query");

String query=queries[0]; System.out.println(query); HttpSession session = req.getSession();

session.setAttribute("lookup.data", query); out.print("set attribute in session");

RequestDispatcher dispatcher = req.getRequestDispatcher("/servlet/DBLookup");

out.print("dispatcher include call"); dispatcher.include(req, res);

out.print("back from dispatcher"); ResultSet rs =(ResultSet) session.getAttribute("result.set");

if(rs!=null){ try{ out.print("<TABLE>\n");

//code here to print out result set as table appears elsewhere. This doGet is in slide notes out.print("</TABLE>\n"); }//try catch(Exception e){out.print("<H1>sql ERROR:</H1> " );} }//if rs!=null else { out.print("<H1>rs is null</H1> " ); }

}

DBLookup: get query from session, connect, and execute a statement, place resultset in session

public void doGet( HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

response.setContentType("text/html"); PrintWriter out = response.getWriter();

try { Connection con = null; Statement stmt = null; ResultSet rs = null; HttpSession session = request.getSession(); String query=(String)session.getAttribute("lookup.data"); out.print("in db servlet get attribute in session"+query);

Class.forName("org.gjt.mm.mysql.Driver"); // Get a Connection to the database con = DriverManager.getConnection( "jdbc:mysql://localhost/test", "root", "");//or user= "root",

pw=""Class.forName("org.gjt.mm.mysql.Driver"); // Get a Connection to the database // JDBC Connection //if (conn == null){ //prepareConnection(); stmt = con.createStatement(); rs = stmt.executeQuery(query); out.print("back from query in dbservlet"); session.setAttribute("result.set",rs); out.print("set rs attribute in session in dbservlet");}catch(Exception e){out.print("sql error");}}

Servlets Chapter 9 database connectivity. Servlets and db Messaging, storefronts and search engines...

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Transcript of Servlets Chapter 9 database connectivity. Servlets and db Messaging, storefronts and search engines...