NullPointerException解析Jsoup [英] NullPointerException Parsing Jsoup

问题描述

使用Jsoup解析网站时，我收到NullPointerException.解析的实际网页根据用户输入而变化.本质上，有时网页上有图像，有时则没有.

I am getting a NullPointerException while using Jsoup to parse a website. The actual webpage which is parsed changes depending on user input. Essentially, sometimes there are images on the webpage and sometimes there are not.

Document doc = Jsoup.connect("http://www.forbes.com/colleges/"+college+"/").get();
Elements photos = doc.select("div[id=photos]");
if(photos!=null){                   
    imgSrc1 = photos.select("li").select("img").first().attr("src");
    input1 = new java.net.URL(imgSrc1).openStream();
    bitmap1 = BitmapFactory.decodeStream(input1);
    image1.setImageBitmap(bitmap1);

}else{
    buffer.append("No Pictures");
}

到目前为止，对于具有图片的网页，它们可以正确显示.对于那些没有图像的对象，我会抛出NPE.我尝试通过检查是否存在id照片"来阻止它，但是仍然出现错误.

As of now, for the webpages which do have images, they show up properly. For those that do not have images, I get a NPE thrown. I tried preventing it by checking whether the id "photos" is present or not, but I am still getting the error.

Logcat:

07-30 16:24:43.497: E/AndroidRuntime(30847): FATAL EXCEPTION: main
07-30 16:24:43.497: E/AndroidRuntime(30847): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.collegeselector/com.collegeselector.CollegeInfo}: java.lang.NullPointerException
07-30 16:24:43.497: E/AndroidRuntime(30847):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
07-30 16:24:43.497: E/AndroidRuntime(30847):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
07-30 16:24:43.497: E/AndroidRuntime(30847):    at android.app.ActivityThread.access$600(ActivityThread.java:141)
07-30 16:24:43.497: E/AndroidRuntime(30847):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
07-30 16:24:43.497: E/AndroidRuntime(30847):    at android.os.Handler.dispatchMessage(Handler.java:99)
07-30 16:24:43.497: E/AndroidRuntime(30847):    at android.os.Looper.loop(Looper.java:137)
07-30 16:24:43.497: E/AndroidRuntime(30847):    at android.app.ActivityThread.main(ActivityThread.java:5039)
07-30 16:24:43.497: E/AndroidRuntime(30847):    at java.lang.reflect.Method.invokeNative(Native Method)
07-30 16:24:43.497: E/AndroidRuntime(30847):    at java.lang.reflect.Method.invoke(Method.java:511)
07-30 16:24:43.497: E/AndroidRuntime(30847):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
07-30 16:24:43.497: E/AndroidRuntime(30847):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
07-30 16:24:43.497: E/AndroidRuntime(30847):    at dalvik.system.NativeStart.main(Native Method)
07-30 16:24:43.497: E/AndroidRuntime(30847): Caused by: java.lang.NullPointerException
07-30 16:24:43.497: E/AndroidRuntime(30847):    at com.collegeselector.CollegeInfo.onCreate(CollegeInfo.java:92)
07-30 16:24:43.497: E/AndroidRuntime(30847):    at android.app.Activity.performCreate(Activity.java:5104)
07-30 16:24:43.497: E/AndroidRuntime(30847):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
07-30 16:24:43.497: E/AndroidRuntime(30847):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
07-30 16:24:43.497: E/AndroidRuntime(30847):    ... 11 more

该如何解决?

示例链接: http://www.forbes.com/colleges/cornell-university/不有照片 http://www.forbes.com/纽约市的大学/哥伦比亚大学/确实有照片

Sample links: http://www.forbes.com/colleges/cornell-university/ does NOT have the photos http://www.forbes.com/colleges/columbia-university-in-the-city-of-new-york/ does have the photos

推荐答案

您需要检查photos元素是否实际包含项

You need to check if your photos element actually contains items

Document doc = Jsoup.connect("http://www.forbes.com/colleges/"+college+"/").get();
Elements photos = doc.select("div[id=photos]");
if(photos!=null && photos.size() > 0){                   
    imgSrc1 = photos.select("li").select("img").first().attr("src");
    input1 = new java.net.URL(imgSrc1).openStream();
    bitmap1 = BitmapFactory.decodeStream(input1);
    image1.setImageBitmap(bitmap1);
}else{
    buffer.append("No Pictures");
}

请注意我添加到您的if语句中的photos.size() > 0. Jsoup中的 select(..)语句不会如果没有元素，则返回null.他们将返回一个空的Elements列表.您只需要检查photos

Notice the photos.size() > 0 I added to your if statement. select(..) statements in Jsoup will not return null if there are no elements. They will return an empty Elements list. You just need to check the size of photos

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