database.java

源码为科学出版社出版的英文<java设计模式>(影印版)所用的所有例子程序

import java.sql.*;
import java.util.*;

class Database {
    Connection con;
    Results results;
    DatabaseMetaData dma;
    String catalog;
    String types[];
    String database_url;

    public Database(String driver) {
        types = new String[1];
        types[0] = "TABLES";         //initialize type array
        try {
            Class.forName(driver);
        }  //load the Bridge driver
        catch (Exception e) {
            System.out.println(e.getMessage());
        }
    }
    //-----------------------------------
    public void close() {
        try {
            con.close();
        } catch (Exception e) {
            System.out.println("close error");
        }

    }
    //-----------------------------------

    public void Open(String url, String cat) {
        catalog = cat;
        database_url = url;
        try {
            con = DriverManager.getConnection(url);
            dma =con.getMetaData();   //get the meta data
        } catch (Exception e) {
            System.out.println(e.getMessage());
        }
    }
    //-----------------------------------
    public void reOpen() {
        try {
            con = DriverManager.getConnection(database_url);
            dma =con.getMetaData();   //get the meta data
        } catch (Exception e) {
            System.out.println(e.getMessage());
        }
    }
    //-----------------------------------
    public String[] getTableNames() {
        String[] tbnames = null;
    Vector tname = new Vector();
    //add the table names to a Vector
    //since we don't know how many there are
        try {
            results = new Results(dma.getTables(catalog, null, "%", types));
        } catch (Exception e) {
            System.out.println(e);
        }

        while (results.hasMoreElements())
            tname.addElement(results.getColumnValue("TABLE_NAME"));


        //copy the table names into a String array
        tbnames = new String[tname.size()];
        for (int i=0; i< tname.size(); i++)
            tbnames[i] = (String)tname.elementAt(i);
        return tbnames;
    }
    //-----------------------------------
    public String[] getTableMetaData() {
        // return the table type information
        results = null;
        try {
            results = new Results(dma.getTables(catalog, null, "%", types));
        } catch (Exception e) {
            System.out.println(e.getMessage());
        }
        return results.getMetaData();
    }
    //-----------------------------------
    public String[] getColumnMetaData(String tablename) {
        //return the data on a column
        results = null;
        try {
            results = new Results(dma.getColumns(catalog, null, tablename, null));
        } catch (Exception e) {
            System.out.println(e.getMessage());
        }
        return results.getMetaData();
    }
    //-----------------------------------
    public String[] getColumnNames(String table) {
        //return an array of Column names
        String[] tbnames = null;
        Vector tname = new Vector();

        try {
            results = new Results(dma.getColumns(catalog, null, table, null));
            while (results.hasMoreElements() )
                tname.addElement(results.getColumnValue("COLUMN_NAME"));  
        } catch (Exception e) {
            System.out.println(e);
        }

        tbnames = new String[tname.size()];
        for (int i=0; i< tname.size(); i++)
            tbnames[i] = (String)tname.elementAt(i);
        return tbnames;
    } 
//-----------------------------------
    public String getColumnValue(String table, String columnName) {
        //return the value of a given column 
        String res = null;
        try {
            if (table.length()>0)
                results = Execute("Select "+columnName+" from "+table+" order by "+columnName);
            if (results.hasMoreElements())
                res = results.getColumnValue(columnName);
        } catch (Exception e) {
            System.out.println("Column value error" +columnName+ e.getMessage());
        }

        return res;
    }
//-----------------------------------
    public String getNextValue(String columnName) {
        // return the next value in that column
        //using the remembered Results
        String res = "";
        try {
            if (results.hasMoreElements())
                res = results.getColumnValue(columnName);
        } catch (Exception e) {
            System.out.println("next value error"+columnName+ e.getMessage());
        }

        return res;
    }
//-----------------------------------
    public Results Execute(String sql) {
        //execute an SQL query on this database
        results = null;
        try {
            Statement stmt = con.createStatement();
            results = new Results(stmt.executeQuery(sql));
        } catch (Exception e) {
            System.out.println("execute error: "+e.getMessage());
        }
        return results;
    }
}