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连接池-归还连接详解(下)

2022-07-28 22:03:00 【汤键.】

目录
适配器设计模式归还数据库连接的思想
适配器设计模式归还数据库连接的实现步骤
适配器设计模式归还数据库连接存在的问题
适配器设计模式归还数据库连接的实例演示
动态代理：
组成：
要求：
实现：
动态代理实例演示
动态代理方式归还数据库连接的思想
动态代理方式归还数据库连接的实现步骤
动态代理方式实例演示
适配器设计模式归还数据库连接的思想
我们可以提供一个适配器类，实现Connection接口，将所有方法进行实现(除了close方法)
自定义连接类只需要继承这个适配器类，重写需要改进的close()方法即可
适配器设计模式归还数据库连接的实现步骤
1.定义一个适配器类，实现Connection接口
2.定义Connection连接对象的成员变量
3.通过有参构造方法完成对成员变量的赋值
4.重写所有方法(除了close)，调用mysql驱动包的连接对象即可
5.定义一个连接类，继承适配器类
6.定义Connection连接对象和连接池容器对象的成员变量，并通过有参构造进行赋值
7.重写close()方法，完成归还连接
8.在自定义连接池中，将获取的连接对象通过自定义连接对象进行包装
适配器设计模式归还数据库连接存在的问题
自定义连接虽然很简洁了，但适配器类还是我们自己编写的，也比较麻烦
适配器设计模式归还数据库连接的实例演示

package demo02.myDataSourse;

import java.sql.*;
import java.util.Map;
import java.util.Properties;
import java.util.concurrent.Executor;
    //1.定义一个适配器类，实现Connection接口
public abstract class myAdapter implements Connection{
    //2.定义连接对象的成员变量
    private Connection con;
    //3.通过有参构造为变量赋值
    public myAdapter(Connection con) {
        this.con = con;
    }
    //4.重写所有的抽象方法(除了close)
        @Override
    public Statement createStatement() throws SQLException {
        return con.createStatement();
    }

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

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

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

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

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

    @Override
    public void commit() throws SQLException {
        con.commit();
    }

    @Override
    public void rollback() throws SQLException {
        con.rollback();
    }

    @Override
    public boolean isClosed() throws SQLException {
        return con.isClosed();
    }

    @Override
    public DatabaseMetaData getMetaData() throws SQLException {
        return con.getMetaData();
    }

    @Override
    public void setReadOnly(boolean readOnly) throws SQLException {
        con.setReadOnly(readOnly);
    }

    @Override
    public boolean isReadOnly() throws SQLException {
        return con.isReadOnly();
    }

    @Override
    public void setCatalog(String catalog) throws SQLException {
        con.setCatalog(catalog);
    }

    @Override
    public String getCatalog() throws SQLException {
        return con.getCatalog();
    }

    @Override
    public void setTransactionIsolation(int level) throws SQLException {
        con.setTransactionIsolation(level);
    }

    @Override
    public int getTransactionIsolation() throws SQLException {
        return con.getTransactionIsolation();
    }

    @Override
    public SQLWarning getWarnings() throws SQLException {
        return con.getWarnings();
    }

    @Override
    public void clearWarnings() throws SQLException {
        con.clearWarnings();
    }

    @Override
    public Statement createStatement(int resultSetType, int resultSetConcurrency) throws SQLException {
        return con.createStatement(resultSetType,resultSetConcurrency);
    }

    @Override
    public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {
        return con.prepareStatement(sql,resultSetType,resultSetConcurrency);
    }

    @Override
    public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {
        return con.prepareCall(sql,resultSetType,resultSetConcurrency);
    }

    @Override
    public Map<String, Class<?>> getTypeMap() throws SQLException {
        return con.getTypeMap();
    }

    @Override
    public void setTypeMap(Map<String, Class<?>> map) throws SQLException {
        con.setTypeMap(map);
    }

    @Override
    public void setHoldability(int holdability) throws SQLException {
        con.setHoldability(holdability);
    }

    @Override
    public int getHoldability() throws SQLException {
        return con.getHoldability();
    }

    @Override
    public Savepoint setSavepoint() throws SQLException {
        return con.setSavepoint();
    }

    @Override
    public Savepoint setSavepoint(String name) throws SQLException {
        return con.setSavepoint(name);
    }

    @Override
    public void rollback(Savepoint savepoint) throws SQLException {
        con.rollback(savepoint);
    }

    @Override
    public void releaseSavepoint(Savepoint savepoint) throws SQLException {
        con.releaseSavepoint(savepoint);
    }

    @Override
    public Statement createStatement(int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {
        return con.createStatement(resultSetType,resultSetConcurrency,resultSetHoldability);
    }

    @Override
    public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {
        return con.prepareStatement(sql,resultSetType,resultSetConcurrency,resultSetHoldability);
    }

    @Override
    public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {
        return con.prepareCall(sql,resultSetType,resultSetConcurrency,resultSetHoldability);
    }

    @Override
    public PreparedStatement prepareStatement(String sql, int autoGeneratedKeys) throws SQLException {
        return con.prepareStatement(sql,autoGeneratedKeys);
    }

    @Override
    public PreparedStatement prepareStatement(String sql, int[] columnIndexes) throws SQLException {
        return con.prepareStatement(sql,columnIndexes);
    }

    @Override
    public PreparedStatement prepareStatement(String sql, String[] columnNames) throws SQLException {
        return con.prepareStatement(sql,columnNames);
    }

    @Override
    public Clob createClob() throws SQLException {
        return con.createClob();
    }

    @Override
    public Blob createBlob() throws SQLException {
        return con.createBlob();
    }

    @Override
    public NClob createNClob() throws SQLException {
        return con.createNClob();
    }

    @Override
    public SQLXML createSQLXML() throws SQLException {
        return con.createSQLXML();
    }

    @Override
    public boolean isValid(int timeout) throws SQLException {
        return con.isValid(timeout);
    }

    @Override
    public void setClientInfo(String name, String value) throws SQLClientInfoException {
        con.setClientInfo(name,value);
    }

    @Override
    public void setClientInfo(Properties properties) throws SQLClientInfoException {
        con.setClientInfo(properties);
    }

    @Override
    public String getClientInfo(String name) throws SQLException {
        return con.getClientInfo(name);
    }

    @Override
    public Properties getClientInfo() throws SQLException {
        return con.getClientInfo();
    }

    @Override
    public Array createArrayOf(String typeName, Object[] elements) throws SQLException {
        return con.createArrayOf(typeName,elements);
    }

    @Override
    public Struct createStruct(String typeName, Object[] attributes) throws SQLException {
        return con.createStruct(typeName,attributes);
    }

    @Override
    public void setSchema(String schema) throws SQLException {
        con.setSchema(schema);
    }

    @Override
    public String getSchema() throws SQLException {
        return con.getSchema();
    }

    @Override
    public void abort(Executor executor) throws SQLException {
        con.abort(executor);
    }

    @Override
    public void setNetworkTimeout(Executor executor, int milliseconds) throws SQLException {
        con.setNetworkTimeout(executor,milliseconds);
    }

    @Override
    public int getNetworkTimeout() throws SQLException {
        return con.getNetworkTimeout();
    }

    @Override
    public <T> T unwrap(Class<T> iface) throws SQLException {
        return con.unwrap(iface);
    }

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

package demo02.myDataSourse;

import java.sql.*;
import java.util.List;
    //1.定义一个类，继承适配器类
public class demomyConnection extends myAdapter {
    //2.定义连接对象和连接池容器对象的成员变量
    private Connection con;
    private List<Connection> pool;
    //3.通过有参构造方法为成员变量赋值
    public demomyConnection(Connection con, List<Connection> pool) {
        super(con);
        this.con = con;
        this.pool = pool;
    }
    //4.重写close方法，完成归还连接
    @Override
    public void close(){
        pool.add(con);
    }
}

package demo02.myDataSourse;
import demo02.utils.JDBCUtils;

import javax.sql.DataSource;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.SQLException;
import java.sql.SQLFeatureNotSupportedException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.logging.Logger;

//自定义数据库连接池
public class demoDataSourse implements DataSource{
    //1.准备容器，用于保存多个连接对象
    private static List<Connection> pool = Collections.synchronizedList(new ArrayList<>());
    //2.定义静态代码块，通过工具类获取10个连接对象
    static{
        for(int i=1;i<=10;i++){
            Connection con = JDBCUtils.getConnection();
            pool.add(con);
        }
    }
    //3.重写getConnection(),用于获取一个连接对象
    @Override
    public Connection getConnection() throws SQLException {
        if(pool.size()>0){
            Connection con = pool.remove(0);
            //通过自定义的连接对象，对原有的连接对象进行包装
            demomyConnection mycon = new demomyConnection(con,pool);
            return mycon;
        }else{
            throw new RuntimeException("连接数量已用尽");
        }
    }
    //4.定义getSize方法，获取连接池容器的大小
    public int getSize(){
        return pool.size();
    }
    @Override
    public Connection getConnection(String username, String password) throws SQLException {
        return null;
    }

    @Override
    public <T> T unwrap(Class<T> iface) throws SQLException {
        return null;
    }

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

    @Override
    public PrintWriter getLogWriter() throws SQLException {
        return null;
    }

    @Override
    public void setLogWriter(PrintWriter out) throws SQLException {

    }

    @Override
    public void setLoginTimeout(int seconds) throws SQLException {

    }

    @Override
    public int getLoginTimeout() throws SQLException {
        return 0;
    }

    @Override
    public Logger getParentLogger() throws SQLFeatureNotSupportedException {
        return null;
    }
}

package demo02.myDataSourse;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;

public class demoDataSourseTest {
    public static void main(String[] args) throws Exception {
        //1.创建连接池对象
        demoDataSourse dataSourse = new demoDataSourse();

        System.out.println("使用之前的数量" + dataSourse.getSize());

        //2.通过连接池对象获取连接对象
        Connection con = dataSourse.getConnection();
        //3.查询学生表的全部信息
        String sql = "SELECT * FROM student";
        PreparedStatement pst = con.prepareStatement(sql);
        //4.执行sql语句,接收结果集
        ResultSet rs = pst.executeQuery();
        //5.处理结果集
        while(rs.next()){
            System.out.println(rs.getInt("sid")+"\t"+rs.getString("name")+"\t"+rs.getInt("age")+"\t"+rs.getDate("birthday"));
        }
        //6.释放资源
        rs.close();
        pst.close();
        con.close();//用完以后，进行归还

        System.out.println("使用之后的数量" + dataSourse.getSize());
    }
}

动态代理：
在不改变目标对象方法的情况下对方法进行增强
组成：
被代理对象：真实的对象
代理对象：内存中的一个对象
代理对象是被代理对象的增强，没有具体的Java文件进行表示，在内存中进行体现
要求：
代理对象和被代理对象实现相同的接口
实现：
Proxy.newProxyInstance()
返回一个代理对象
参数：
1.类加载器
如stu.getClass().getClassLoader()
2.接口类型Class数组
如new Class[]{StudentInterface.class}
3.代理规则
通过匿名内部类的方式使用InvocationHandler接口
这个接口里有一个invoke方法
第一个参数不需要关心，一般用不到
第二个参数method:我们所要调用某个对象真实的方法的Method对象
第三个参数args:是传递给增强执行方法的具体的参数
动态代理实例演示
被代理对象

package demo02.laodemo;

public class Student implements StudentInterface{
    public void eat(String name){
        System.out.println("学生吃"+name);
    }
    public void study(){
        System.out.println("在家自学");
    }
}

接口

package demo02.laodemo;

public interface StudentInterface {
    void eat(String name);
    void study();
}

代理对象

package demo02.laodemo;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

public class Test {
    public static void main(String[] args) {
        Student stu = new Student();
        //要求：在不改动Student类中任何的代码的前提下，通过study方法输出一句话：我在刷codeforces
        StudentInterface proxystu = (StudentInterface) Proxy.newProxyInstance(stu.getClass().getClassLoader(), new Class[]{StudentInterface.class}, new InvocationHandler() {
            @Override
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                //执行Student类中所有的方法都会经过invoke方法
                //对method方法进行判断
                //如果是study，则对其进行增强；如果不是，还调用学生对象原有的功能即可
                if(method.getName().equals("study")){
                    System.out.println("我在刷codeforces");
                    return null;
                }else{
                    return method.invoke(stu,args);
                }
            }
        });
        proxystu.eat("米饭");
        proxystu.study();
    }
}

动态代理方式归还数据库连接的思想
我们可以通过Proxy来完成对Connection实现类对象的代理
代理过程中判断如果执行的是close方法，就将连接归还池中
如果是其它方法则调用连接对象原来的功能即可
动态代理方式归还数据库连接的实现步骤
1.定义一个类，实现DataSource接口
2.定义一个容器，用于保存多个Connection连接对象
3.定义静态代码块，通过JDBC工具类获取10个连接保存到容器中
4.重写getConnection方法，从容器中获取一个连接
5.通过Proxy代理，如果是close方法，就将连接归还池中，如果是其它方法则调用原有功能
6.定义getSize方法，用于获取容器的大小并返回
动态代理方式实例演示

package demo02.myDataSourse;
import demo02.utils.JDBCUtils;

import javax.sql.DataSource;
import java.io.PrintWriter;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.sql.Connection;
import java.sql.SQLException;
import java.sql.SQLFeatureNotSupportedException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.logging.Logger;

//自定义数据库连接池
public class demoDataSourse implements DataSource{
    //1.准备容器，用于保存多个连接对象
    private static List<Connection> pool = Collections.synchronizedList(new ArrayList<>());
    //2.定义静态代码块，通过工具类获取10个连接对象
    static{
        for(int i=1;i<=10;i++){
            Connection con = JDBCUtils.getConnection();
            pool.add(con);
        }
    }
    //3.重写getConnection(),用于获取一个连接对象
    @Override
    public Connection getConnection() throws SQLException {
        if(pool.size()>0){
            Connection con = pool.remove(0);
            //执行Connection实现类连接对象所有的方法都会经过invoke
            //如果是close方法，就将连接归还池中，如果是其它方法则调用原有功能
            Connection proxycon = (Connection) Proxy.newProxyInstance(con.getClass().getClassLoader(), new Class[]{Connection.class}, new InvocationHandler() {
                @Override
                public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                    if(method.getName().equals("close")){
                        pool.add(con);
                        return null;
                    }else{
                        return method.invoke(con,args);
                    }
                }
            });
            return proxycon;
        }else{
            throw new RuntimeException("连接数量已用尽");
        }
    }
    //4.定义getSize方法，获取连接池容器的大小
    public int getSize(){
        return pool.size();
    }
    @Override
    public Connection getConnection(String username, String password) throws SQLException {
        return null;
    }

    @Override
    public <T> T unwrap(Class<T> iface) throws SQLException {
        return null;
    }

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

    @Override
    public PrintWriter getLogWriter() throws SQLException {
        return null;
    }

    @Override
    public void setLogWriter(PrintWriter out) throws SQLException {

    }

    @Override
    public void setLoginTimeout(int seconds) throws SQLException {

    }

    @Override
    public int getLoginTimeout() throws SQLException {
        return 0;
    }

    @Override
    public Logger getParentLogger() throws SQLFeatureNotSupportedException {
        return null;
    }
}

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版权声明
本文为[汤键.]所创，转载请带上原文链接，感谢
https://blog.csdn.net/weixin_59624686/article/details/126019789