ExecuteSQLpublic class ExecuteSQL extends Object | A general-purpose SQL interpreter program. |
| Methods Summary |
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| public static void | main(java.lang.String[] args)
Connection conn = null; // Our JDBC connection to the database server
try {
String driver = null, url = null, user = "", password = "";
// Parse all the command-line arguments
for(int n = 0; n < args.length; n++) {
if (args[n].equals("-d")) driver = args[++n];
else if (args[n].equals("-u")) user = args[++n];
else if (args[n].equals("-p")) password = args[++n];
else if (url == null) url = args[n];
else throw new IllegalArgumentException("Unknown argument.");
}
// The only required argument is the database URL.
if (url == null)
throw new IllegalArgumentException("No database specified");
// If the user specified the classname for the DB driver, load
// that class dynamically. This gives the driver the opportunity
// to register itself with the DriverManager.
if (driver != null) Class.forName(driver);
// Now open a connection the specified database, using the user-specified
// username and password, if any. The driver manager will try all of
// the DB drivers it knows about to try to parse the URL and connect to
// the DB server.
conn = DriverManager.getConnection(url, user, password);
// Now create the statement object we'll use to talk to the DB
Statement s = conn.createStatement();
// Get a stream to read from the console
BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
// Loop forever, reading the user's queries and executing them
while(true) {
System.out.print("sql> "); // prompt the user
System.out.flush(); // make the prompt appear immediately
String sql = in.readLine(); // get a line of input from the user
// Quit when the user types "quit".
if ((sql == null) || sql.equals("quit")) break;
// Ignore blank lines
if (sql.length() == 0) continue;
// Now, attempt to execute the user's line of SQL and display results.
try {
// We don't know if this is a query or some kind of update, so we
// use execute() instead of executeQuery() or executeUpdate()
// If the return value is true, it was a query, else an update
boolean status = s.execute(sql);
// Loop until there are no more results to return
do {
if (status) { // statement was a query that returns a ResultSet
// Get the set of results and display them
ResultSet rs = s.getResultSet();
printResultsTable(rs, System.out);
}
else {
// If the SQL command that was executed was some kind of update
// rather than a query, then it doesn't return a ResultSet.
// Instead, we just print the number of rows that were affected.
int numUpdates = s.getUpdateCount();
System.out.println("Ok. " + numUpdates + " rows affected.");
}
// Now go see if there are even more results, and
// continue the results display loop if there are.
status = s.getMoreResults();
// With some buggy JDBC drivers, this condition causes an infinite
// loop with SQL updates. If that happens, change to: while(status);
} while(status || s.getUpdateCount() != -1);
}
// If a SQLException is thrown, display an error message. Note that
// SQLExceptions can have a general message and a DB-specific message
// returned by getSQLState()
catch (SQLException e) {
System.err.println("SQLException: " + e.getMessage() + ":" +
e.getSQLState());
}
// Each time through this loop, check to see if any warnings were
// issued. Note that there can be a whole chain of warnings.
finally { // print out any warnings that occurred
for(SQLWarning w=conn.getWarnings(); w != null; w=w.getNextWarning())
System.err.println("WARNING: " + w.getMessage() +
":" + w.getSQLState());
}
}
}
// Handle exceptions that occur during argument parsing, database
// connection setup, etc. For SQLExceptions, print the details.
catch (Exception e) {
System.err.println(e);
if (e instanceof SQLException)
System.err.println("SQL State: " + ((SQLException)e).getSQLState());
System.err.println("Usage: java ExecuteSQL [-d <driver>] [-u <user>] " +
"[-p <password>] <database URL>");
}
// Be sure to always close the database connection when we exit, whether
// we exit because the user types 'quit' or because of an exception thrown
// while setting things up. Closing this connection also implicitly
// closes any open statements and result sets associated with it.
finally {
try { conn.close(); } catch (Exception e) {}
}
| | static void | overwrite(java.lang.StringBuffer b, int pos, java.lang.String s)This utility method is used when printing the table of results
int len = s.length();
for(int i = 0; i < len; i++) b.setCharAt(pos+i, s.charAt(i));
| | static void | printResultsTable(java.sql.ResultSet rs, java.io.OutputStream output)This method attempts to output the contents of a ResultSet in a
textual table. It relies on the ResultSetMetaData class, but a fair
bit of the code is simple string manipulation.
// Set up the output stream
PrintWriter out = new PrintWriter(new OutputStreamWriter(output));
// Get some "meta data" (column names, etc.) about the results
ResultSetMetaData metadata = rs.getMetaData();
// Variables to hold important data about the table to be displayed
int numcols = metadata.getColumnCount();// how many columns
String[] labels = new String[numcols]; // the column labels
int[] colwidths = new int[numcols]; // the width of each
int[] colpos = new int[numcols]; // start position of each
int linewidth; // total width of table
// Figure out how wide the columns are, where each one begins,
// how wide each row of the table will be, etc.
linewidth = 1; // for the initial '|'.
for(int i = 0; i < numcols; i++) { // for each column
colpos[i] = linewidth; // save its position
labels[i] = metadata.getColumnLabel(i+1); // get its label
// Get the column width. If the db doesn't report one, guess
// 30 characters. Then check the length of the label, and use
// it if it is larger than the column width
int size = metadata.getColumnDisplaySize(i+1);
if (size == -1) size = 30; // some drivers return -1...
int labelsize = labels[i].length();
if (labelsize > size) size = labelsize;
colwidths[i] = size + 1; // save the column the size
linewidth += colwidths[i] + 2; // increment total size
}
// Create a horizontal divider line we use in the table.
// Also create a blank line that is the initial value of each
// line of the table
StringBuffer divider = new StringBuffer(linewidth);
StringBuffer blankline = new StringBuffer(linewidth);
for(int i = 0; i < linewidth; i++) {
divider.insert(i, '-");
blankline.insert(i, " ");
}
// Put special marks in the divider line at the column positions
for(int i=0; i<numcols; i++) divider.setCharAt(colpos[i]-1,'+");
divider.setCharAt(linewidth-1, '+");
// Begin the table output with a divider line
out.println(divider);
// The next line of the table contains the column labels.
// Begin with a blank line, and put the column names and column
// divider characters "|" into it. overwrite() is defined below.
StringBuffer line = new StringBuffer(blankline.toString());
line.setCharAt(0, '|");
for(int i = 0; i < numcols; i++) {
int pos = colpos[i] + 1 + (colwidths[i]-labels[i].length())/2;
overwrite(line, pos, labels[i]);
overwrite(line, colpos[i] + colwidths[i], " |");
}
// Then output the line of column labels and another divider
out.println(line);
out.println(divider);
// Now, output the table data. Loop through the ResultSet, using
// the next() method to get the rows one at a time. Obtain the
// value of each column with getObject(), and output it, much as
// we did for the column labels above.
while(rs.next()) {
line = new StringBuffer(blankline.toString());
line.setCharAt(0, '|");
for(int i = 0; i < numcols; i++) {
Object value = rs.getObject(i+1);
overwrite(line, colpos[i] + 1, value.toString().trim());
overwrite(line, colpos[i] + colwidths[i], " |");
}
out.println(line);
}
// Finally, end the table with one last divider line.
out.println(divider);
out.flush();
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