JDBC之连接池

 

     在JDBC编程中，如果反复的创建连接，进行数据库的查询，这样会使系统性能大大降低，为了重复利用Connection，所以引入了连接池的

 

概念，下面看看我的最简单的连接池.V1.0版。

 

      因为我的Connection不能被别人随便的new，所以采用了单利模式。

 

package viekie.du.jdbc;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.LinkedList;

public class ConnectionPool {
   
    private static final String url = "jdbc:mysql://localhost:3306/jdbc";
    private static final String user = "root";
    private static final String password = "duchaolihaixu";
   
    public static final int MAX_CONNECTION_NUMBER = 5;
    public static final int EMPTY_POOL = -100;
   
    private static int connectionNumbers = 0;
   
    private static ConnectionPool instance = null;

    private LinkedList<Connection> listPool = new LinkedList<Connection>();   
   
    private ConnectionPool() throws Exception{
        for(int i=0; i<5; i++){
            this.listPool.addFirst(this.createConnection());
            connectionNumbers ++;
        }
    }
   
    public static ConnectionPool getInstance() throws Exception{
        if(null==instance){
            synchronized(ConnectionPool.class){           
                if(null==instance){
                    instance = new ConnectionPool();
                }           
            }           
        }
        return instance;
    }
   
    public Connection getConnection() throws SQLException{

        if(this.listPool!=null && this.listPool.size()>0){
            connectionNumbers --;
            return listPool.removeFirst();
        }else{
            throw new SQLException("the connection is empty or null");
        }
    }
   
    private Connection createConnection() throws Exception{
       
        Class.forName("com.mysql.jdbc.Driver");
        DatabaseConnection conn = new DatabaseConnection(DriverManager.getConnection(url, user, password),this);
       
        return conn;
    }

    public int getSize(){
       
        if(connectionNumbers>=0){
            return connectionNumbers;
        }
        return EMPTY_POOL;
    }
   
    public void setSize(int size){
        connectionNumbers = size;
    }

    public void add(Connection conn) {
   
        this.listPool.addLast(conn);
    }
}

 

     在来看看我的Connection的包装。

package viekie.du.jdbc;

import java.sql.Array;
import java.sql.Blob;
import java.sql.CallableStatement;
import java.sql.Clob;
import java.sql.Connection;
import java.sql.DatabaseMetaData;
import java.sql.NClob;
import java.sql.PreparedStatement;
import java.sql.SQLClientInfoException;
import java.sql.SQLException;
import java.sql.SQLWarning;
import java.sql.SQLXML;
import java.sql.Savepoint;
import java.sql.Statement;
import java.sql.Struct;
import java.util.Map;
import java.util.Properties;

public class DatabaseConnection implements Connection {

    private Connection conn = null;
    private ConnectionPool connPool= null;
   
    public DatabaseConnection(Connection conn, ConnectionPool pool){
        this.conn = conn;
        this.connPool = pool;
    }
    @Override
    public <T> T unwrap(Class<T> iface) throws SQLException {
        return null;
    }

    @Override
    public boolean isWrapperFor(Class<?> iface) throws SQLException {
        return false;
    }

    @Override
    public Statement createStatement() throws SQLException {
        return null;
    }

    @Override
    public PreparedStatement prepareStatement(String sql) throws SQLException {
        return null;
    }

    @Override
    public CallableStatement prepareCall(String sql) throws SQLException {
        return null;
    }

    @Override
    public String nativeSQL(String sql) throws SQLException {
        return null;
    }

    @Override
    public void setAutoCommit(boolean autoCommit) throws SQLException {
    }

    @Override
    public boolean getAutoCommit() throws SQLException {
        return false;
    }

    @Override
    public void commit() throws SQLException {
    }
    @Override
    public void rollback() throws SQLException {
    }
    @Override
    public void close() throws SQLException {
        if(null!=this){
            int size = this.connPool.getSize();
            if(size<ConnectionPool.MAX_CONNECTION_NUMBER){
                this.connPool.add(this);
                this.connPool.setSize(size++);
            }else{
                conn.close();
            }           
        }
    }
    @Override
    public boolean isClosed() throws SQLException {
        return false;
    }

    @Override
    public DatabaseMetaData getMetaData() throws SQLException {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public void setReadOnly(boolean readOnly) throws SQLException {
        // TODO Auto-generated method stub

    }

    @Override
    public boolean isReadOnly() throws SQLException {
        // TODO Auto-generated method stub
        return false;
    }

    @Override
    public void setCatalog(String catalog) throws SQLException {
        // TODO Auto-generated method stub

    }

    @Override
    public String getCatalog() throws SQLException {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public void setTransactionIsolation(int level) throws SQLException {
        // TODO Auto-generated method stub

    }

    @Override
    public int getTransactionIsolation() throws SQLException {
        // TODO Auto-generated method stub
        return 0;
    }

    @Override
    public SQLWarning getWarnings() throws SQLException {
        // TODO Auto-generated method stub
        return null;
    }
    @Override
    public void clearWarnings() throws SQLException {
    }

    @Override
    public Statement createStatement(int resultSetType, int resultSetConcurrency)
            throws SQLException {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public PreparedStatement prepareStatement(String sql, int resultSetType,
            int resultSetConcurrency) throws SQLException {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public CallableStatement prepareCall(String sql, int resultSetType,
            int resultSetConcurrency) throws SQLException {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public Map<String, Class<?>> getTypeMap() throws SQLException {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public void setTypeMap(Map<String, Class<?>> map) throws SQLException {
        // TODO Auto-generated method stub

    }

    @Override
    public void setHoldability(int holdability) throws SQLException {
        // TODO Auto-generated method stub

    }

    @Override
    public int getHoldability() throws SQLException {
        // TODO Auto-generated method stub
        return 0;
    }
    @Override
    public Savepoint setSavepoint() throws SQLException {
        return null;
    }
    @Override
    public Savepoint setSavepoint(String name) throws SQLException {
        return null;
    }
    @Override
    public void rollback(Savepoint savepoint) throws SQLException {
    }
    @Override
    public void releaseSavepoint(Savepoint savepoint) throws SQLException {
        // TODO Auto-generated method stub

    }

    @Override
    public Statement createStatement(int resultSetType,
            int resultSetConcurrency, int resultSetHoldability)
            throws SQLException {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public PreparedStatement prepareStatement(String sql, int resultSetType,
            int resultSetConcurrency, int resultSetHoldability)
            throws SQLException {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public CallableStatement prepareCall(String sql, int resultSetType,
            int resultSetConcurrency, int resultSetHoldability)
            throws SQLException {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public PreparedStatement prepareStatement(String sql, int autoGeneratedKeys)
            throws SQLException {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public PreparedStatement prepareStatement(String sql, int[] columnIndexes)
            throws SQLException {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public PreparedStatement prepareStatement(String sql, String[] columnNames)
            throws SQLException {
        return null;
    }
    @Override
    public Clob createClob() throws SQLException {
        return null;
    }
    @Override
    public Blob createBlob() throws SQLException {
        return null;
    }
    @Override
    public NClob createNClob() throws SQLException {
        return null;
    }
    @Override
    public SQLXML createSQLXML() throws SQLException {
        return null;
    }
    @Override
    public boolean isValid(int timeout) throws SQLException {
        return false;
    }
    @Override
    public void setClientInfo(String name, String value)
            throws SQLClientInfoException {
    }
    @Override
    public void setClientInfo(Properties properties)
            throws SQLClientInfoException {
    }
    @Override
    public String getClientInfo(String name) throws SQLException {
        return null;
    }
    @Override
    public Properties getClientInfo() throws SQLException {
        return null;
    }
    @Override
    public Array createArrayOf(String typeName, Object[] elements)
            throws SQLException {
        return null;
    }
    @Override
    public Struct createStruct(String typeName, Object[] attributes)
            throws SQLException {
        return null;
    }
}

    我的Connection对MySQL的Connection进行了包装，采用了代理模式，这样在connection的close调用的时候，就可以被我自定的

 

connection所捕获，然后，根据连接池的状态，重新把connection放入到连接池中或者关闭。