Android Studio-使用jsoup进行解析时抛出错误(java.lang.NullPointerException)
我正在尝试从网站中挖掘一个表的数据,将其存储到Android Studio-使用jsoup进行解析时抛出错误(java.lang.NullPointerException),java,android,jsoup,Java,Android,Jsoup,我正在尝试从网站中挖掘一个表的数据,将其存储到ArrayList中,并在ListView布局中查看它。每次我运行程序时都会出现这个错误 04-29 23:52:57.122 20095-20095/com.example.user.datamining E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.project.datamining, PID: 20095 java.lang.RuntimeException: Una
ArrayList
中,并在ListView
布局中查看它。每次我运行程序时都会出现这个错误
04-29 23:52:57.122 20095-20095/com.example.user.datamining E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.project.datamining, PID: 20095
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.user.datamining/com.example.user.DataMining}: java.lang.NullPointerException: Attempt to invoke virtual method 'org.jsoup.select.Elements org.jsoup.nodes.Document.select(java.lang.String)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2521)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2595)
at android.app.ActivityThread.access$800(ActivityThread.java:178)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1470)
at android.os.Handler.dispatchMessage(Handler.java:111)
at android.os.Looper.loop(Looper.java:194)
at android.app.ActivityThread.main(ActivityThread.java:5631)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:959)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:754)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'org.jsoup.select.Elements org.jsoup.nodes.Document.select(java.lang.String)' on a null object reference
这是我的代码:
package com.example.user.datamining;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;
import org.jsoup.select.Elements;
import java.io.IOException;
import java.util.ArrayList;
public class DataMining extends AppCompatActivity {
Document doc;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_data_mining);
Thread downloadThread = new Thread() {
public void run() {
try {
doc = Jsoup.connect("http://thewebsite.html").get();
} catch (IOException e) {
e.printStackTrace();
}
}
};
downloadThread.start();
ArrayList<String> list = new ArrayList();
Elements table = doc.select("table");
Elements rows = table.select("tr");
for (int i = 0; i < rows.size(); i++) {
org.jsoup.nodes.Element row = rows.get(i);
Elements cols = row.select("td");
list.add(cols.get(i).text());
ArrayAdapter<String> adapter = new ArrayAdapter(this, R.layout.datalayout, list);
ListView view = (ListView) findViewById(R.id.dataListView);
view.setAdapter(adapter);
}
}
}
package com.example.user.datamining;
导入android.os.Bundle;
导入android.support.v7.app.AppActivity;
导入android.widget.ArrayAdapter;
导入android.widget.ListView;
导入org.jsoup.jsoup;
导入org.jsoup.nodes.Document;
导入org.jsoup.select.Elements;
导入java.io.IOException;
导入java.util.ArrayList;
公共类数据挖掘扩展了AppCompative活动{
文件文件;
@凌驾
创建时受保护的void(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity\u data\u mining);
线程下载线程=新线程(){
公开募捐{
试一试{
doc=Jsoup.connect(“http://thewebsite.html).get();
}捕获(IOE异常){
e、 printStackTrace();
}
}
};
downloadThread.start();
ArrayList=新建ArrayList();
元素表=文件选择(“表”);
元素行=表。选择(“tr”);
对于(inti=0;i
您正在启动一个单独的线程来执行下载,并初始化doc
。此线程异步运行,因此在启动线程后立即对其调用select()
时,doc
仍为null
在线程的run()
方法中将解析代码移动到下载后,并在解析后使用Activity
的runOnUiThread()
方法设置ListView
的Adapter
,因为您不能从下载线程直接触摸View
private Document doc;
private ArrayList<String> list = new ArrayList<>();
@Override
protected void onCreat(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_data_mining);
Thread downloadThread = new Thread() {
public void run() {
try {
doc = Jsoup.connect("http://thewebsite.html").get();
Elements table = doc.select("table");
Elements rows = table.select("tr");
for (int i = 0; i < rows.size(); i++) {
org.jsoup.nodes.Element row = rows.get(i);
Elements cols = row.select("td");
list.add(cols.get(i).text());
}
runOnUiThread(new Runnable() {
@Override
public void run() {
setListAdapter();
}
}
);
}
catch (IOException e) {
e.printStackTrace();
}
}
};
downloadThread.start();
}
private void setListAdapter() {
ArrayAdapter<String> adapter = new ArrayAdapter<>(this, R.layout.datalayout, list);
ListView view = (ListView) findViewById(R.id.dataListView);
view.setAdapter(adapter);
}
私人文件文档;
private ArrayList list=new ArrayList();
@凌驾
创建时受保护的void(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity\u data\u mining);
线程下载线程=新线程(){
公开募捐{
试一试{
doc=Jsoup.connect(“http://thewebsite.html).get();
元素表=文件选择(“表”);
元素行=表。选择(“tr”);
对于(inti=0;i
doc
在调用select()
时,它是null
,因为在此之前启动的downloadThread
尚未完成,这可能是您初始化它的地方。那么我该怎么办@米肯,哦,是的,你把帖子贴在那里了。我没看见。给我一分钟,我会重新组织你的代码。非常感谢你,我刚刚完成了我想用这个类做的事情,一切都在相应地工作!!