安卓和 JSON。捕获异常 - 错误的链接

Question

我正在制作一个通过 JSON 与服务器通信的应用程序。用户可以输入服务器的地址，当用户输入错误的链接时，我想提供受控的行为。我不想通过捕获一般异常来隐藏问题，我想捕获特定的异常，但我不知道如何。

这是一个日志，当用户输入错误的链接时：

01-19 00:08:10.205: W/dalvikvm(12576): threadid=12: thread exiting with uncaught exception (group=0x410af2a0)
01-19 00:08:10.220: E/AndroidRuntime(12576): FATAL EXCEPTION: AsyncTask #1
01-19 00:08:10.220: E/AndroidRuntime(12576): java.lang.RuntimeException: An error     occured while executing doInBackground()
01-19 00:08:10.220: E/AndroidRuntime(12576):    at     android.os.AsyncTask$3.done(AsyncTask.java:299)
01-19 00:08:10.220: E/AndroidRuntime(12576):    at     java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
01-19 00:08:10.220: E/AndroidRuntime(12576):    at     java.util.concurrent.FutureTask.setException(FutureTask.java:124)
01-19 00:08:10.220: E/AndroidRuntime(12576):    at     java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
01-19 00:08:10.220: E/AndroidRuntime(12576):    at     java.util.concurrent.FutureTask.run(FutureTask.java:137)
01-19 00:08:10.220: E/AndroidRuntime(12576):    at     android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
01-19 00:08:10.220: E/AndroidRuntime(12576):    at     java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
01-19 00:08:10.220: E/AndroidRuntime(12576):    at     java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
01-19 00:08:10.220: E/AndroidRuntime(12576):    at     java.lang.Thread.run(Thread.java:856)
01-19 00:08:10.220: E/AndroidRuntime(12576): Caused by: java.lang.IllegalStateException:     Target host must not be null, or set in parameters. scheme=null, host=null, path=aaaaaasss
01-19 00:08:10.220: E/AndroidRuntime(12576):    at     org.apache.http.impl.client.DefaultRequestDirector.determineRoute(DefaultRequestDirector.jav    a:591)
01-19 00:08:10.220: E/AndroidRuntime(12576):    at     org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:293)
01-19 00:08:10.220: E/AndroidRuntime(12576):    at         org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:670)
01-19 00:08:10.220: E/AndroidRuntime(12576):    at     org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:509)
01-19 00:08:10.220: E/AndroidRuntime(12576):    at     org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:487)
01-19 00:08:10.220: E/AndroidRuntime(12576):    at     pl.mosek.micro.JSONParser.makeHttpRequestJSONObject(JSONParser.java:62)
01-19 00:08:10.220: E/AndroidRuntime(12576):    at     pl.mosek.micro.SignInActivity$UserLoginTask.doInBackground(SignInActivity.java:287)
01-19 00:08:10.220: E/AndroidRuntime(12576):    at     pl.mosek.micro.SignInActivity$UserLoginTask.doInBackground(SignInActivity.java:1)
01-19 00:08:10.220: E/AndroidRuntime(12576):    at     android.os.AsyncTask$2.call(AsyncTask.java:287)
01-19 00:08:10.220: E/AndroidRuntime(12576):    at     java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
01-19 00:08:10.220: E/AndroidRuntime(12576):    ... 5 more

这是 JSONParser 类：

public class JSONParser {

static InputStream is = null;
static JSONObject jObj = null;
static JSONArray jArray = null;
static String json = "";
private boolean started = false;
private boolean finished = false;

public static String getJson() {
    return json;
}

// constructor
public JSONParser() {

}

// function get json from url
// by making HTTP POST or GET mehtod
public JSONObject makeHttpRequestJSONObject(String url, String method,
        List<NameValuePair> params) {

    finished = false;
    started = true;

    // Making HTTP request
    try {

        // check for request method
        if (method == "POST") {
            // request method is POST
            // defaultHttpClient
            DefaultHttpClient httpClient = new DefaultHttpClient();
            HttpPost httpPost = new HttpPost(url);
            httpPost.setEntity(new UrlEncodedFormEntity(params));

            HttpResponse httpResponse = httpClient.execute(httpPost);
            HttpEntity httpEntity = httpResponse.getEntity();
            is = httpEntity.getContent();

        } else if (method == "GET") {
            // request method is GET
            DefaultHttpClient httpClient = new DefaultHttpClient();
            String paramString = URLEncodedUtils.format(params, "utf-8");
            url += "?" + paramString;
            HttpGet httpGet = new HttpGet(url);

            HttpResponse httpResponse = httpClient.execute(httpGet);
            HttpEntity httpEntity = httpResponse.getEntity();
            is = httpEntity.getContent();
        }

    } catch (UnsupportedEncodingException e) {
        e.printStackTrace();
    } catch (ClientProtocolException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }

    try {
        BufferedReader reader = new BufferedReader(new InputStreamReader(
                is, "iso-8859-1"), 8);
        StringBuilder sb = new StringBuilder();
        String line = null;
        while ((line = reader.readLine()) != null) {
            sb.append(line + "\n");
        }
        is.close();
        json = sb.toString();
    } catch (Exception e) {
        Log.e("Buffer Error", "Error converting result " + e.toString());
    }

    // try parse the string to a JSON object
    try {
        jObj = new JSONObject(json);
    } catch (JSONException e) {
        Log.e("JSON Parser", "Error parsing data " + e.toString());
    }

    started = false;
    finished = true;
    // return JSON String
    return jObj;

}

public JSONArray makeHttpRequestJSONArray(String url, String method,
        List<NameValuePair> params) {

    finished = false;
    started = true;

    // Making HTTP request
    try {

        // check for request method
        if (method == "POST") {
            // request method is POST
            // defaultHttpClient
            DefaultHttpClient httpClient = new DefaultHttpClient();
            HttpPost httpPost = new HttpPost(url);
            httpPost.setEntity(new UrlEncodedFormEntity(params));

            HttpResponse httpResponse = httpClient.execute(httpPost);
            HttpEntity httpEntity = httpResponse.getEntity();
            is = httpEntity.getContent();

        } else if (method == "GET") {
            // request method is GET
            DefaultHttpClient httpClient = new DefaultHttpClient();
            String paramString = URLEncodedUtils.format(params, "utf-8");
            url += "?" + paramString;
            HttpGet httpGet = new HttpGet(url);

            HttpResponse httpResponse = httpClient.execute(httpGet);
            HttpEntity httpEntity = httpResponse.getEntity();
            is = httpEntity.getContent();
        }

    } catch (UnsupportedEncodingException e) {
        e.printStackTrace();
    } catch (ClientProtocolException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }

    try {
        BufferedReader reader = new BufferedReader(new InputStreamReader(
                is, "iso-8859-1"), 8);
        StringBuilder sb = new StringBuilder();
        String line = null;
        while ((line = reader.readLine()) != null) {
            sb.append(line + "\n");
        }
        is.close();
        json = sb.toString();
    } catch (Exception e) {
        Log.e("Buffer Error", "Error converting result " + e.toString());
    }

    // try parse the string to a JSON object
    try {
        jArray = new JSONArray(json);
    } catch (JSONException e) {
        Log.e("JSON Parser", "Error parsing data " + e.toString());
    }

    started = false;
    finished = true;
    // return JSON String
    return jArray;

}

public boolean isStarted() {
    return started;
}

public boolean isFinished() {
    return finished;
}

}

我应该怎么做才能捕获特定的异常？

Answer 1

你可以抓到：

IllegalStateException (Exception e)

或者您可以在执行请求之前检查输入是否有错误。

Answer 2

pl.mosek.micro.JSONParser.makeHttpRequestJSONObject(JSONParser.java:62)

我不知道你的线在哪里（62），但你可以看到错误：

目标主机不能为空，或在参数中设置。方案=空， 主机=null，路径=aaaaaass

我认为你应该在使用前检查 null。

在这一行：

httpPost.setEntity(new UrlEncodedFormEntity(params));

参数是否为空？

几乎很重要，请检查您的 InputStream

BufferedReader reader = new BufferedReader(new InputStreamReader(is, "iso-8859-1"), 8);

is 是否为空？

Answer 3

您正在以 Java 无法做到的方式比较字符串。

应该是：

if ("POST".equals(method))

你们中没有一个 IF 评估为 true，因此您没有设置 URL，并且 HTTP 对象令人窒息。