如何使用 throw 处理 Android 中的异常

Question

我正在尝试从网站获取信息并将其显示在 Android 应用中。问题“What is the fastest way to scrape HTML webpage in Android?”的第二个答案建议使用 BufferedReader。在答案中，此人使用 URL 类。我试图实现这样的答案：

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.widget.TextView;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

import java.net.URL;

public class MainActivity extends AppCompatActivity {
    TextView display = (TextView) findViewById(R.id.textDisplay);

    @Override
    protected void onCreate(Bundle savedInstanceState) throws Exception {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        URL url = new URL("http://stackoverflow.com/questions/2971155");
        BufferedReader reader = null;
        StringBuilder builder = new StringBuilder();
        try {
            reader = new BufferedReader(new InputStreamReader(url.openStream(), "UTF-8"));
            for (String line; (line = reader.readLine()) != null; ) {
                builder.append(line.trim());
            }
        } finally {
            if (reader != null) {
                try {
                    reader.close();
                } catch (IOException logOrIgnore) {
                    logOrIgnore.printStackTrace();
                }
            }
        }
        String start = "<div class=\"post-text\"><p>";
        String end = "</p>";
        String part = builder.substring(builder.indexOf(start) + start.length());
        String question = part.substring(0, part.indexOf(end));
        TextView display = (TextView) findViewById(R.id.textDisplay);
        display.setText(question);

    }


}

我收到了这个错误：

'onCreate(Bundle)' in 'com.example.myproject.MainActivity' clashes with 
'onCreate(Bundle)' in 'android.appcompat.app.AppCompatActivity';
 overridden method does not throw 'java.lang.Exception'

您建议如何处理这个问题，这是从网站获取数据的明智方式吗？ 非常感谢任何帮助

Answer 1

像这样修改代码

    public class MainActivity extends AppCompatActivity {
        TextView display = (TextView) findViewById(R.id.textDisplay);

        @Override
        protected void onCreate(Bundle savedInstanceState) throws Exception {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);

try{
            URL url = new URL("http://stackoverflow.com/questions/2971155");
            BufferedReader reader = null;
            StringBuilder builder = new StringBuilder();
            try {
                reader = new BufferedReader(new InputStreamReader(url.openStream(), "UTF-8"));
                for (String line; (line = reader.readLine()) != null; ) {
                    builder.append(line.trim());
                }
            } finally {
                if (reader != null) {
                    try {
                        reader.close();
                    } catch (IOException logOrIgnore) {
                        logOrIgnore.printStackTrace();
                    }
                }
            }
            String start = "<div class=\"post-text\"><p>";
            String end = "</p>";
            String part = builder.substring(builder.indexOf(start) + start.length());
            String question = part.substring(0, part.indexOf(end));
            TextView display = (TextView) findViewById(R.id.textDisplay);
            display.setText(question);
}catch(Exception ex){
Log.e("EEXCCEption","ex.localizedMessage.toString()")

}

        }


    }

在 Logger 文件中你可以得到异常的实际原因。

Answer 2

首先 - onCreate() 应该是 public，而不是 protected。 其次，onCreate()的签名不会抛出异常，所以覆盖的时候不能加。如果你真的想扔，那么你能做的最好的就是从方法签名中删除throws，catch，将它包装在RuntimeException中并重新扔：

try {
  // .. your code
} catch(Exception e){
    throw new RuntimeException(e);
}finally {
            if (reader != null) {
                try {
                    reader.close();
                } catch (IOException logOrIgnore) {
                    logOrIgnore.printStackTrace();
                }
            }
        }

Answer 3

onCreate() 方法是Activity 生命周期的一部分，您只是覆盖它（注意@Override），而不是编写自己的，因此您无法更改属性、返回类型或添加/删除throws 声明

从protected void onCreate(Bundle savedInstanceState) throws Exception { 中删除throws Exception - 这会导致您的异常

并使用try{}catch{}，例如

try {
    reader = new BufferedReader(new InputStreamReader(url.openStream(), "UTF-8"));
    for (String line; (line = reader.readLine()) != null; ) {
        builder.append(line.trim());
    }
} catch(Exception e){
    e.printStackTrace();
    //TODO handle exception by own, don't throw outside onCreate, it will break lifecycle
} finally {
    ...

@Neeraj 这不是真的，事实上这是你可以改变的唯一一件事 - 类可访问性（public，protected 等） - 但仅适用于“更易访问”版本，所以 protected 到public，但不是例如public 到 private。顺便提一句。其实super这个方法的版本是protected，@MamoRatzo没改，没关系