Guest Book Servlet
/*
Database Programming with JDBC and Java, Second Edition
By George Reese
ISBN: 1-56592-616-1
Publisher: O'Reilly
*/
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.Date;
import java.sql.Driver;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Locale;
import java.util.Properties;
import java.util.Random;
import java.util.StringTokenizer;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class GuestBookServlet extends HttpServlet {
private Properties connectionProperties = new Properties();
private Driver driver = null;
private String driverName = null;
private String jdbcURL = null;
private Random random = new Random();
/**
* Provides the servlet with the chance to get runtime configuration values
* and initialize itself. For a database servlet, you want to grab the
* driver name, URL, and any connection information. For this example, I
* assume a driver that requires a user name and password. For an example of
* more database independent configuration, see Chapter 4.
*
* @param cfg
* the servlet configuration information
* @throws javax.servlet.ServletException
* could not load the specified JDBC driver
*/
public void init(ServletConfig cfg) throws ServletException {
super.init(cfg);
{
String user, pw;
driverName = cfg.getInitParameter("gb.driver");
jdbcURL = cfg.getInitParameter("gb.jdbcURL");
user = cfg.getInitParameter("gb.user");
if (user != null) {
connectionProperties.put("user", user);
}
pw = cfg.getInitParameter("gb.pw");
if (pw != null) {
connectionProperties.put("password", pw);
}
try {
driver = (Driver) Class.forName(driverName).newInstance();
} catch (Exception e) {
throw new ServletException("Unable to load driver: "
+ e.getMessage());
}
}
}
/**
* Performs the HTTP GET. This is where we print out a form and a random
* sample of the comments.
*
* @param req
* the servlet request information
* @param res
* the servlet response information
* @throws javax.servlet.ServletException
* an error occurred talking to the database
* @throws java.io.IOException
* a socket error occurred
*/
public void doGet(HttpServletRequest req, HttpServletResponse res)
throws ServletException, IOException {
PrintWriter out = res.getWriter();
Locale loc = getLocale(req);
res.setContentType("text/html");
printCommentForm(out, loc);
printComments(out, loc);
}
public void doPost(HttpServletRequest req, HttpServletResponse res)
throws ServletException, IOException {
PrintWriter out = res.getWriter();
Locale loc = getLocale(req);
String name, email, comment;
Connection conn = null;
Exception err = null;
int id = -1;
String[] tmp;
// get the form values
tmp = req.getParameterValues("name");
if (tmp == null || tmp.length != 1) {
name = null;
} else {
name = tmp[0];
}
tmp = req.getParameterValues("email");
if (tmp == null || tmp.length != 1) {
email = null;
} else {
email = tmp[0];
}
tmp = req.getParameterValues("comments");
if (tmp == null || tmp.length != 1) {
comment = null;
} else {
comment = tmp[0];
}
res.setContentType("text/html");
// validate values
if (name.length() < 1) {
out.println("You must specify a valid name!");
printCommentForm(out, loc);
return;
}
if (email.length() < 3) {
out.println("You must specify a valid email address!");
printCommentForm(out, loc);
return;
}
if (email.indexOf("@") < 1) {
out.println("You must specify a valid email address!");
printCommentForm(out, loc);
return;
}
if (comment.length() < 1) {
out.println("You left no comments!");
printCommentForm(out, loc);
return;
}
try {
SimpleDateFormat fmt = new SimpleDateFormat("yyyy-MM-dd", Locale.US);
java.util.Date date = new java.util.Date();
ResultSet result;
Statement stmt;
conn = DriverManager.getConnection(jdbcURL, connectionProperties);
// remove the "setAutoCommit(false)" line for mSQL or MySQL
conn.setAutoCommit(false);
stmt = conn.createStatement();
// generate a new comment ID
// more on ID generation in Chapter 4
result = stmt.executeQuery("SELECT NEXT_SEQ " + "FROM SEQGEN "
+ "WHERE NAME = 'COMMENT_ID'");
if (!result.next()) {
throw new ServletException("Failed to generate id.");
}
id = result.getInt(1) + 1;
stmt.close();
// closing the statement closes the result
stmt = conn.createStatement();
stmt.executeUpdate("UPDATE SEQGEN SET NEXT_SEQ = " + id
+ " WHERE NAME = 'COMMENT_ID'");
stmt.close();
stmt = conn.createStatement();
comment = fixComment(comment);
stmt.executeUpdate("INSERT INTO COMMENT "
+ "(COMMENT_ID, EMAIL, NAME, COMMENT, " + "CMT_DATE) "
+ "VALUES (" + id + ", '" + email + "', '" + name + "', '"
+ comment + "', '" + fmt.format(date) + "')");
conn.commit();
stmt.close();
} catch (SQLException e) {
e.printStackTrace();
err = e;
} finally {
if (conn != null) {
try {
conn.close();
} catch (Exception e) {
}
}
}
if (err != null) {
out.println("An error occurred on save: " + err.getMessage());
} else {
printCommentForm(out, loc);
printComments(out, loc);
}
}
/**
* Find the desired locale from the HTTP header.
*
* @param req
* the servlet request from which the header is read
* @return the locale matching the first accepted language
*/
private Locale getLocale(HttpServletRequest req) {
String hdr = req.getHeader("Accept-Language");
StringTokenizer toks;
if (hdr == null) {
return Locale.getDefault();
}
toks = new StringTokenizer(hdr, ",");
if (toks.hasMoreTokens()) {
String lang = toks.nextToken();
int ind = lang.indexOf(';');
Locale loc;
if (ind != -1) {
lang = lang.substring(0, ind);
}
lang = lang.trim();
ind = lang.indexOf("-");
if (ind == -1) {
loc = new Locale(lang, "");
} else {
loc = new Locale(lang.substring(0, ind), lang
.substring(ind + 1));
}
return loc;
}
return Locale.getDefault();
}
public String getServletInfo() {
return "Guest Book Servlet\nFrom Database Programming with JDBC "
+ "and Java";
}
private void printCommentForm(PrintWriter out, Locale loc)
throws IOException {
out.println("<div class=\"gbform\">");
out.println("<form action=\"personal/guestbook.shtml\" "
+ "method=\"POST\">");
out.println("<table>");
out.println("<tr>");
out.println("<td>Name:</td>");
out.println("<td><input type=\"text\" name=\"name\" "
+ "size=\"30\"/></td>");
out.println("<td><input type=\"submit\" value=\"Save\"/></td>");
out.println("</tr>");
out.println("<tr>");
out.println("<td>Email:</td>");
out.println("<td><input type=\"text\" name=\"email\" "
+ "size=\"30\"/></td>");
out.println("<tr>");
out.println("<tr>");
out.println("<td>Comments:</td>");
out.println("<tr>");
out.println("<tr>");
out.println("<td colspan=\"3\">");
out.println("<textarea name=\"comments\" cols=\"40\" rows=\"7\">");
out.println("</textarea></td>");
out.println("<tr>");
out.println("</table>");
out.println("</form>");
}
private void printComments(PrintWriter out, Locale loc) throws IOException {
Connection conn = null;
try {
DateFormat fmt = DateFormat.getDateInstance(DateFormat.FULL, loc);
ResultSet results;
Statement stmt;
int rows, count;
conn = DriverManager.getConnection(jdbcURL, connectionProperties);
stmt = conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_READ_ONLY);
results = stmt.executeQuery("SELECT NAME, EMAIL, CMT_DATE, "
+ "COMMENT, COMMENT_ID " + "FROM COMMENT "
+ "ORDER BY CMT_DATE");
out.println("<dl>");
results.last();
results.next();
rows = results.getRow();
// pick a random row
rows = random.nextInt() % rows;
if (rows < 4) {
// if the random row is less than 4, print the first 4 rows
results.afterLast();
} else {
// otherwise go to the specified row, print the prior 5 rows
results.absolute(rows);
}
count = 0;
// print up to 5 rows going backwards from the randomly
// selected row
while (results.previous() && (count < 5)) {
String name, email, cmt;
Date date;
count++;
name = results.getString(1);
if (results.wasNull()) {
name = "Unknown User";
}
email = results.getString(2);
if (results.wasNull()) {
email = "user@host";
}
date = results.getDate(3);
if (results.wasNull()) {
date = new Date((new java.util.Date()).getTime());
}
cmt = results.getString(4);
if (results.wasNull()) {
cmt = "No comment.";
}
out.println("<dt><b>" + name + "</b> (" + email + ") on "
+ fmt.format(date) + "</dt>");
cmt = noXML(cmt);
out.println("<dd> " + cmt + "</dd>");
}
out.println("</dl>");
} catch (SQLException e) {
out.println("A database error occurred: " + e.getMessage());
} finally {
if (conn != null) {
try {
conn.close();
} catch (SQLException e) {
}
}
}
}
/**
* Removes any XML-sensitive characters from a comment and replaces them
* with their character entities.
*
* @param cmt
* the raw comment
* @return the XML-safe comment
*/
private String noXML(String cmt) {
StringBuffer buff = new StringBuffer();
for (int i = 0; i < cmt.length(); i++) {
char c = cmt.charAt(i);
switch (c) {
case '<':
buff.append("<");
break;
case '>':
buff.append(">");
break;
case '&':
buff.append("&");
break;
case '"':
buff.append(""");
break;
default:
buff.append(c);
break;
}
}
return buff.toString();
}
/**
* This method escapes single quotes so that database statements are not
* messed up.
*
* @param comment
* the raw comment
* @return a comment with any quotes escaped
*/
private String fixComment(String comment) {
if (comment.indexOf("'") != -1) {
String tmp = "";
for (int i = 0; i < comment.length(); i++) {
char c = comment.charAt(i);
if (c == '\'') {
tmp = tmp + "\\'";
} else {
tmp = tmp + c;
}
}
comment = tmp;
}
return comment;
}
}
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