Question

所以我创建了一个向网站发送请求的小方法，我想确保它没有崩溃。当我断开互联网并调用方法时，我得到一个java.net.UnknownHostException:，但我无法抓住它。我究竟做错了什么？

提供问题的行是HttpResponse response = httpclient.execute(httppost);

我甚至在IO之前处理ClientProtocolException（IO的子类），所以我可以同时拥有两个catch块。我还尝试为高级throws clauses添加Exception e。这是我的代码：

public String connect(String username, String password) {
    String answer = "Could not connect to server, please check your internet connect or try later.";
    try {
        DefaultHttpClient httpclient = new DefaultHttpClient();
        HttpPost httppost = new HttpPost(baseurl);
        // Request parameters and other properties.
        List<NameValuePair> params = new ArrayList<NameValuePair>(2);
        params.add(new BasicNameValuePair("usernameUS", username));
        params.add(new BasicNameValuePair("passwordUS", password));
        httppost.setEntity(new UrlEncodedFormEntity(params, "UTF-8"));

        // Execute and get the response.
        HttpResponse response = httpclient.execute(httppost);
        HttpEntity entity = response.getEntity();

        if (entity != null) {
            answer = EntityUtils.toString(entity, charset);
            try {
                if (answer.equals("Authenticated")) {
                    this.password = password;
                    this.username = username;
                    Authenticated = true;
                    return answer;
                } else {
                    return answer;
                }
            } finally {
            }
        }
        return "Could not connect to server, please try later.";
    } catch (ClientProtocolException ex) {
        Logger.getLogger(Connection.class.getName()).log(Level.SEVERE,
                null, ex);
        return answer;
    } catch (IOException ex) {
        Logger.getLogger(Connection.class.getName()).log(Level.SEVERE,
                null, ex);
        return answer;
    }
}

例外：

java.net.UnknownHostException: www.example.com
    at java.net.Inet6AddressImpl.lookupAllHostAddr(Native Method)
    at java.net.InetAddress$1.lookupAllHostAddr(InetAddress.java:866)
    at java.net.InetAddress.getAddressesFromNameService(InetAddress.java:1258)
    at java.net.InetAddress.getAllByName0(InetAddress.java:1211)
    at java.net.InetAddress.getAllByName(InetAddress.java:1127)
    at java.net.InetAddress.getAllByName(InetAddress.java:1063)
    at org.apache.http.impl.conn.SystemDefaultDnsResolver.resolve(SystemDefaultDnsResolver.java:45)
    at org.apache.http.impl.conn.DefaultClientConnectionOperator.resolveHostname(DefaultClientConnectionOperator.java:278)
    at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:162)
    at org.apache.http.impl.conn.ManagedClientConnectionImpl.open(ManagedClientConnectionImpl.java:294)
    at org.apache.http.impl.client.DefaultRequestDirector.tryConnect(DefaultRequestDirector.java:640)
    at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:479)
    at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:906)
    at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:805)
    at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:784)
    at usclient.Connection.connect(Connection.java:65)

工作代码：

public class Connection {
private static Connection conn;
String username, fileURL;
String baseurl = "http://www.example.com";
String content, password = "";
String charset = "UTF-8";
HttpURLConnection request;
URL url;
OutputStreamWriter post;
BufferedReader in;

private Connection()    {
}

public static Connection getInstance()  {
    if(conn==null)  {
        conn = new Connection();
    }
    return conn;
}

public String connect(String username, String password){
    String answer = "Could not connect to server, please check your internet connect or try later.";
    try {
        DefaultHttpClient httpclient = new DefaultHttpClient();
        HttpPost httppost = new HttpPost(baseurl);
        // Request parameters and other properties.
        List<NameValuePair> params = new ArrayList<NameValuePair>(2);
        params.add(new BasicNameValuePair("usernameUS", username));
        params.add(new BasicNameValuePair("passwordUS", password));
        httppost.setEntity(new UrlEncodedFormEntity(params, "UTF-8"));

        //Execute and get the response.
        HttpResponse response = httpclient.execute(httppost);
        HttpEntity entity = response.getEntity();
        if (entity != null) {
            String[] data = EntityUtils.toString(entity, charset).split("\\n");
            answer = data[0];
            try {
                if(answer.contentEquals("Authenticated")) {
                    this.password = password;
                    this.username = username;
                    if(data.length<1)
                        fileURL = data[1];
                    return data[0];
                }
                else {
                    return answer;
                }
            } finally {
            }
        }
        return "Could not connect to server, please try later.";
    } catch (ClientProtocolException ex) {
        Logger.getLogger(Connection.class.getName()).log(Level.SEVERE, "Exception caught:", ex);
        return empty;
    } catch (IOException ex) {
        Logger.getLogger(Connection.class.getName()).log(Level.SEVERE, "Exception caught:", ex);
        return empty;
    } 
}

Answer 1

我敢肯定，这个问题应该被关闭。为什么呢？

我刚检查了您提供的相关来源。

您的班级Connection的最后一个版本甚至不想编译。 Java抱怨声明return empty;。这个变量是什么empty？

好的，即使将return empty;更改为return answer;（例如） - 一切运作良好。

例如，如果我尝试连接到http://www.fdsfsaddsfsddsafasd.com，则java.net.UnknownHostException语句会成功捕获...catch(IOException ...。

我建议您完全重建项目，在调试模式下运行并再次进行测试。

IOException没有捕获java.net.UnknownHostException：

1 个答案: