Socket兼容IP和域名的原因

小灰灰 2022-12-13 04:06 92阅读 0赞

测试代码

//将172.16.12.171 替换为 xingyun25 打印结果一致
    Socket sock = new Socket("172.16.12.171",12331); 
    InetAddress netAddress = sock.getInetAddress();
    
    System.out.println(netAddress.getHostName());
    System.out.println(netAddress.getHostAddress());
    sock.close();

打印结果

xingyun25
    172.16.12.171

查看 `Socket` 方法

public Socket(String host, int port) throws UnknownHostException, IOException
        { 
           //host != null 因此第一个参数为new InetSocketAddress(host, port)
           this(host != null ? new InetSocketAddress(host, port) :
                 new InetSocketAddress(InetAddress.getByName(null), 
                 //第二个参数 (SocketAddress) null 
                 //第三个参数 true 
                 (SocketAddress) null, true);
        }

查看 `this` 构造方法

private Socket(SocketAddress address, SocketAddress localAddr,
                       boolean stream) throws IOException { 
        setImpl();
    
        // backward compatibility
        if (address == null)
            throw new NullPointerException();
    
        try { 
            createImpl(stream);
            if (localAddr != null)
                //localhost/127.0.0.1
                bind(localAddr);
            //建立连接
            connect(address);
        } catch (IOException | IllegalArgumentException | SecurityException e) { 
            try { 
                close();
            } catch (IOException ce) { 
                e.addSuppressed(ce);
            }
            throw e;
        }
    }

对于 `setImpl` 方法

void setImpl() {
        if (factory != null) {
            impl = factory.createSocketImpl();
            checkOldImpl();
        } else {
            // No need to do a checkOldImpl() here, we know it's an up to date
            // SocketImpl!
            impl = new SocksSocketImpl();
        }
    
        //Impl SET Socket 
        if (impl != null)
            impl.setSocket(this);
    }

对于 `createImpl` 方法

// SocketImpl impl ：The implementation of this Socket. 
    void createImpl(boolean stream) throws SocketException { 
        if (impl == null)
            setImpl();
        try { 
            impl.create(stream);
            created = true;
        } catch (IOException e) { 
            throw new SocketException(e.getMessage());
        }
    }

查看`InetSocketAddress`方法通过`IP`和域名创建有何不同

public InetSocketAddress(String hostname, int port) {
            checkHost(hostname);
            InetAddress addr = null;
    		String host = null;
            try {
                addr = InetAddress.getByName(hostname);
            } catch(UnknownHostException e){
               host = hostname;
            }
            //实际构造了 InetSocketAddressHolder 
            holder = new InetSocketAddressHolder(host, addr, checkPort(port));
        }

`connect` 过程中实际使用的是 `InetAddress`

private InetSocketAddressHolder(String hostname, InetAddress addr, int port) { 
                this.hostname = hostname;
                 this.addr = addr;
                this.port = port;
    }