JDBC连接池原理、自定义连接池代码实现
首先自己实现一个简单的连接池：
数据准备：
CREATE DATABASE mybase;
USE mybase;
CREATE TABLE users(
uid INT PRIMARY KEY AUTO_INCREMENT,
username VARCHAR(64),
upassword VARCHAR(64)
);
INSERT INTO users (username,upassword) VALUES("zhangsan","123"),("lisi","456"),("wangwu","789");
SELECT * FROM users;
提取JDBC工具类：
package demo; import java.io.InputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.Properties; public class JDBCUtils3 {
public static String driver;
public static String url;
public static String username;
public static String password; static {
try {
ClassLoader classLoader = JDBCUtils3.class.getClassLoader();
InputStream is = classLoader.getResourceAsStream("db.properties");
Properties props = new Properties();
props.load(is);
driver = props.getProperty("driver");
url = props.getProperty("url");
username = props.getProperty("username");
password = props.getProperty("password");
} catch (Exception ex) {
ex.printStackTrace();
}
} public static Connection getConnection() {
Connection conn = null;
try {
Class.forName(driver);
conn = DriverManager.getConnection(url, username, password);
} catch (Exception ex) {
ex.printStackTrace();
}
return conn;
} public static void release(Connection conn, PreparedStatement pstmt, ResultSet rs) {
if (rs != null) {
try {
rs.close();
} catch (Exception e) {
e.printStackTrace();
}
}
if (pstmt != null) {
try {
pstmt.close();
} catch (Exception e) {
e.printStackTrace();
}
}
if (conn != null) {
try {
conn.close();
} catch (Exception e) {
e.printStackTrace();
}
} }
}
配置文件db.properties：
driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/mybase
username=root
password=xuyiqing
自定义连接池：
package demo1; import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.SQLException;
import java.sql.SQLFeatureNotSupportedException;
import java.util.LinkedList;
import java.util.logging.Logger; import javax.sql.DataSource; import demo.JDBCUtils3; public class MyDataSource implements DataSource{
//1.创建1个容器用于存储Connection对象
private static LinkedList<Connection> pool = new LinkedList<Connection>(); //2.创建5个连接放到容器中去
static{
for (int i = 0; i < 5; i++) {
Connection conn = JDBCUtils3.getConnection();
pool.add(conn);
}
} /**
* 重写获取连接的方法
*/
@Override
public Connection getConnection() throws SQLException {
Connection conn = null;
//3.使用前先判断
if(pool.size()==0){
//4.池子里面没有，我们再创建一些
for (int i = 0; i < 5; i++) {
conn = JDBCUtils3.getConnection();
pool.add(conn);
}
}
//5.从池子里面获取一个连接对象Connection
conn = pool.remove(0);
return conn;
} /**
* 归还连接对象到连接池中去
*/
public void backConnection(Connection conn){
pool.add(conn);
} @Override
public PrintWriter getLogWriter() throws SQLException {
// TODO Auto-generated method stub
return null;
} @Override
public void setLogWriter(PrintWriter out) throws SQLException {
// TODO Auto-generated method stub } @Override
public void setLoginTimeout(int seconds) throws SQLException {
// TODO Auto-generated method stub } @Override
public int getLoginTimeout() throws SQLException {
// TODO Auto-generated method stub
return 0;
} @Override
public Logger getParentLogger() throws SQLFeatureNotSupportedException {
// TODO Auto-generated method stub
return null;
} @Override
public <T> T unwrap(Class<T> iface) throws SQLException {
// TODO Auto-generated method stub
return null;
} @Override
public boolean isWrapperFor(Class<?> iface) throws SQLException {
// TODO Auto-generated method stub
return false;
} @Override
public Connection getConnection(String username, String password) throws SQLException {
// TODO Auto-generated method stub
return null;
} }
测试：
package demo1; import java.sql.Connection;
import java.sql.PreparedStatement; import org.junit.Test; public class TestMyDataSource {
@Test
public void testAddUser() {
Connection conn = null;
PreparedStatement pstmt = null;
// 1.创建自定义连接池对象
MyDataSource dataSource = new MyDataSource();
try {
// 2.从池子中获取连接
conn = dataSource.getConnection();
String sql = "insert into users values(null,?,?)";
pstmt = conn.prepareStatement(sql);
pstmt.setString(1, "吕布");
pstmt.setString(2, "貂蝉");
int rows = pstmt.executeUpdate();
if (rows > 0) {
System.out.println("添加成功!");
} else {
System.out.println("添加失败!");
}
} catch (Exception e) {
throw new RuntimeException(e);
} finally {
dataSource.backConnection(conn);
}
}
}
测试：输出：添加成功!
接下来要做到放回连接的时候，调用了close方法却不是关闭资源，而是放回到池中
这时候需要一个自定义类实现Connection接口
package demo1; 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.LinkedList;
import java.util.Map;
import java.util.Properties;
import java.util.concurrent.Executor; //1.实现同一个接口Connection
public class MyConnection implements Connection {
//3.定义一个变量
private Connection conn; private LinkedList<Connection> pool; // 2.编写一个构造方法(参数使用了面相对象的多态特性)
public MyConnection(Connection conn,LinkedList<Connection> pool) {
this.conn=conn;
this.pool=pool;
} //4.书写需要增强的方法
@Override
public void close() throws SQLException {
pool.add(conn);
} /**
* 此方法必须覆盖！否则会出现空指针异常！！！
*/
@Override
public PreparedStatement prepareStatement(String sql) throws SQLException {
return conn.prepareStatement(sql);
} @Override
public <T> T unwrap(Class<T> iface) throws SQLException {
// TODO Auto-generated method stub
return null;
} @Override
public boolean isWrapperFor(Class<?> iface) throws SQLException {
// TODO Auto-generated method stub
return false;
} @Override
public Statement createStatement() throws SQLException {
// TODO Auto-generated method stub
return null;
} @Override
public CallableStatement prepareCall(String sql) throws SQLException {
// TODO Auto-generated method stub
return null;
} @Override
public String nativeSQL(String sql) throws SQLException {
// TODO Auto-generated method stub
return null;
} @Override
public void setAutoCommit(boolean autoCommit) throws SQLException {
// TODO Auto-generated method stub } @Override
public boolean getAutoCommit() throws SQLException {
// TODO Auto-generated method stub
return false;
} @Override
public void commit() throws SQLException {
// TODO Auto-generated method stub } @Override
public void rollback() throws SQLException {
// TODO Auto-generated method stub } @Override
public boolean isClosed() throws SQLException {
// TODO Auto-generated method stub
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 {
// TODO Auto-generated method stub } @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 {
// TODO Auto-generated method stub
return null;
} @Override
public Savepoint setSavepoint(String name) throws SQLException {
// TODO Auto-generated method stub
return null;
} @Override
public void rollback(Savepoint savepoint) throws SQLException {
// TODO Auto-generated method stub } @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 {
// TODO Auto-generated method stub
return null;
} @Override
public Clob createClob() throws SQLException {
// TODO Auto-generated method stub
return null;
} @Override
public Blob createBlob() throws SQLException {
// TODO Auto-generated method stub
return null;
} @Override
public NClob createNClob() throws SQLException {
// TODO Auto-generated method stub
return null;
} @Override
public SQLXML createSQLXML() throws SQLException {
// TODO Auto-generated method stub
return null;
} @Override
public boolean isValid(int timeout) throws SQLException {
// TODO Auto-generated method stub
return false;
} @Override
public void setClientInfo(String name, String value) throws SQLClientInfoException {
// TODO Auto-generated method stub } @Override
public void setClientInfo(Properties properties) throws SQLClientInfoException {
// TODO Auto-generated method stub } @Override
public String getClientInfo(String name) throws SQLException {
// TODO Auto-generated method stub
return null;
} @Override
public Properties getClientInfo() throws SQLException {
// TODO Auto-generated method stub
return null;
} @Override
public Array createArrayOf(String typeName, Object[] elements) throws SQLException {
// TODO Auto-generated method stub
return null;
} @Override
public Struct createStruct(String typeName, Object[] attributes) throws SQLException {
// TODO Auto-generated method stub
return null;
} @Override
public void setSchema(String schema) throws SQLException {
// TODO Auto-generated method stub } @Override
public String getSchema() throws SQLException {
// TODO Auto-generated method stub
return null;
} @Override
public void abort(Executor executor) throws SQLException {
// TODO Auto-generated method stub } @Override
public void setNetworkTimeout(Executor executor, int milliseconds) throws SQLException {
// TODO Auto-generated method stub } @Override
public int getNetworkTimeout() throws SQLException {
// TODO Auto-generated method stub
return 0;
} }
修改自定义连接池类：
package demo1; import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.SQLException;
import java.sql.SQLFeatureNotSupportedException;
import java.util.LinkedList;
import java.util.logging.Logger; import javax.sql.DataSource; import demo.JDBCUtils3; public class MyDataSource implements DataSource {
// 1.创建1个容器用于存储Connection对象
private static LinkedList<Connection> pool = new LinkedList<Connection>(); // 2.创建5个连接放到容器中去
static {
for (int i = 0; i < 5; i++) {
Connection conn = JDBCUtils3.getConnection();
// 放入池子中connection对象已经经过改造了
MyConnection myconn = new MyConnection(conn, pool);
pool.add(myconn);
}
} /**
* 重写获取连接的方法
*/
@Override
public Connection getConnection() throws SQLException {
Connection conn = null;
// 3.使用前先判断
if (pool.size() == 0) {
// 4.池子里面没有，我们再创建一些
for (int i = 0; i < 5; i++) {
conn = JDBCUtils3.getConnection();
// 放入池子中connection对象已经经过改造了
MyConnection myconn = new MyConnection(conn, pool);
pool.add(myconn);
}
}
// 5.从池子里面获取一个连接对象Connection
conn = pool.remove(0);
return conn;
} /**
* 归还连接对象到连接池中去
*/
public void backConnection(Connection conn) {
pool.add(conn);
} @Override
public PrintWriter getLogWriter() throws SQLException {
// TODO Auto-generated method stub
return null;
} @Override
public void setLogWriter(PrintWriter out) throws SQLException {
// TODO Auto-generated method stub } @Override
public void setLoginTimeout(int seconds) throws SQLException {
// TODO Auto-generated method stub } @Override
public int getLoginTimeout() throws SQLException {
// TODO Auto-generated method stub
return 0;
} @Override
public Logger getParentLogger() throws SQLFeatureNotSupportedException {
// TODO Auto-generated method stub
return null;
} @Override
public <T> T unwrap(Class<T> iface) throws SQLException {
// TODO Auto-generated method stub
return null;
} @Override
public boolean isWrapperFor(Class<?> iface) throws SQLException {
// TODO Auto-generated method stub
return false;
} @Override
public Connection getConnection(String username, String password) throws SQLException {
// TODO Auto-generated method stub
return null;
} }
测试：
package demo1; import java.sql.Connection;
import java.sql.PreparedStatement; import javax.sql.DataSource; import org.junit.Test; import demo.JDBCUtils3; public class TestMyDataSource {
@Test
public void testAddUser1() {
Connection conn = null;
PreparedStatement pstmt = null;
// 1.创建自定义连接池对象
DataSource dataSource = new MyDataSource();
try {
// 2.从池子中获取连接
conn = dataSource.getConnection();
String sql = "insert into users values(null,?,?)";
//3.必须在自定义的connection类中重写prepareStatement(sql)方法
pstmt = conn.prepareStatement(sql);
pstmt.setString(1, "吕布1");
pstmt.setString(2, "貂蝉1");
int rows = pstmt.executeUpdate();
if (rows > 0) {
System.out.println("添加成功!");
} else {
System.out.println("添加失败!");
}
} catch (Exception e) {
throw new RuntimeException(e);
} finally {
JDBCUtils3.release(conn, pstmt, null);
}
}
}
添加成功！
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