java.net.unknownhostexception 异常-ag捕鱼王app官网

本篇文章介绍了 java 中的 java.net.unknownhostexception 错误。

java中java.net.unknownhostexception的原因

java.net.unknownhostexception 表示找不到主机名的 ip 地址。 通常，当主机名输入错误时会发生这种情况。

此异常的另一个原因是 dns 配置错误或 dns 传播。 新的 dns 可能需要 48 小时才能在整个互联网上传播。

下面是 java 中 unknownhostexception 的示例：

package jiyik;
import java.io.ioexception;
import java.net.httpurlconnection;
import java.net.malformedurlexception;
import java.net.url;
public class example {
    public static void main(string[] args) {
        string host_name = "https://delftstack.co";
        url demo_url = null;
        try {
            demo_url = new url(host_name);
            httpurlconnection demo_connection = (httpurlconnection) demo_url.openconnection();
            system.out.println(demo_connection.getresponsecode());
        } catch (malformedurlexception me) {
            me.printstacktrace();
        } catch (ioexception ie) {
            ie.printstacktrace();
        }
    }
}

上面尝试连接到主机，但主机名有输入错误。 它将抛出 unknownhostexception。

查看输出：

java.net.unknownhostexception: delftstack.co
    at java.base/sun.nio.ch.niosocketimpl.connect(niosocketimpl.java:567)
    at java.base/java.net.sockssocketimpl.connect(sockssocketimpl.java:327)
    at java.base/java.net.socket.connect(socket.java:633)
    at java.base/sun.security.ssl.sslsocketimpl.connect(sslsocketimpl.java:299)
    at java.base/sun.security.ssl.basesslsocketimpl.connect(basesslsocketimpl.java:174)
    at java.base/sun.net.networkclient.doconnect(networkclient.java:183)
    at java.base/sun.net.www.http.httpclient.openserver(httpclient.java:498)
    at java.base/sun.net.www.http.httpclient.openserver(httpclient.java:603)
    at java.base/sun.net.www.protocol.https.httpsclient.(httpsclient.java:266)
    at java.base/sun.net.www.protocol.https.httpsclient.new(httpsclient.java:380)
    at java.base/sun.net.www.protocol.https.abstractdelegatehttpsurlconnection.getnewhttpclient(abstractdelegatehttpsurlconnection.java:189)
    at java.base/sun.net.www.protocol.http.httpurlconnection.plainconnect0(httpurlconnection.java:1242)
    at java.base/sun.net.www.protocol.http.httpurlconnection.plainconnect(httpurlconnection.java:1128)
    at java.base/sun.net.www.protocol.https.abstractdelegatehttpsurlconnection.connect(abstractdelegatehttpsurlconnection.java:175)
    at java.base/sun.net.www.protocol.http.httpurlconnection.getinputstream0(httpurlconnection.java:1665)
    at java.base/sun.net.www.protocol.http.httpurlconnection.getinputstream(httpurlconnection.java:1589)
    at java.base/java.net.httpurlconnection.getresponsecode(httpurlconnection.java:529)
    at java.base/sun.net.www.protocol.https.httpsurlconnectionimpl.getresponsecode(httpsurlconnectionimpl.java:308)
    at jiyik.example.main(example.java:16)

java.net.unknownhostexception 是一个已检查异常，可以使用 try-catch 块进行处理。 请参阅下面如何处理 java 中的 unknownhostexception：

package jiyik;
import java.io.ioexception;
import java.net.httpurlconnection;
import java.net.malformedurlexception;
import java.net.url;
import java.net.unknownhostexception;
public class example {
    public static void main(string[] args) {
        string host_name = "https://delftstack.co";
        url demo_url = null;
        try {
            demo_url = new url(host_name);
            httpurlconnection demo_connection = (httpurlconnection) demo_url.openconnection();
            system.out.println(demo_connection.getresponsecode());
        } catch (unknownhostexception ue) {
            ue.printstacktrace();
        } catch (malformedurlexception me) {
            me.printstacktrace();
        } catch (ioexception ie) {
            ie.printstacktrace();
        }
    }
}

防止java中的java.net.unknownhostexception

为了防止java中出现 java.net.unknownhostexception，我们应该考虑以下两点：

1. 首先，确保主机名正确并且没有任何输入错误 - 仔细检查是否有任何输入错误或空格。
2. 检查 dns 设置以确保服务器可访问。 新主机名需要一段时间才能跟上 dns 服务器的速度。

让我们使用正确的主机名尝试相同的示例。 参见示例：

package jiyik;
import java.io.ioexception;
import java.net.httpurlconnection;
import java.net.malformedurlexception;
import java.net.url;
import java.net.unknownhostexception;
public class example {
    public static void main(string[] args) {
        string host_name = "http://localhost/";
        url demo_url = null;
        try {
            demo_url = new url(host_name);
            httpurlconnection demo_connection = (httpurlconnection) demo_url.openconnection();
            system.out.println(demo_connection.getresponsecode());
        } catch (unknownhostexception uhe) {
            uhe.printstacktrace();
        } catch (malformedurlexception me) {
            me.printstacktrace();
        } catch (ioexception ie) {
            ie.printstacktrace();
        }
    }
}

上面的代码将正常工作并打印响应代码。 查看输出：

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