Grouping and adding up BigDecimals using Java Stream API

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• Android PDF Viewer null object reference error

  I am using barteksc Android PDF Viewer like many others (https://github.com/barteksc/AndroidPdfViewer). I keep receiving a null object reference error. This is the error.

  E/AndroidRuntime: FATAL EXCEPTION: main
                    Process: group6.interactivehandwriting, PID: 24037
                    java.lang.RuntimeException: Unable to start activity ComponentInfo{group6.interactivehandwriting/group6.interactivehandwriting.activities.RoomActivity.RoomActivity}: android.view.InflateException: Binary XML file line #9: Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on a null object reference
  

  I have checked to make sure I am referencing the views correctly. The asset I am loading called "sample.pdf" is in my assets.

  * Can you see any reason why I am receiving this error? *

  I realize there are multiple post about this library, however every instance seems to be unique so I decided to go ahead and ask.

  RoomActivity.java

  package group6.interactivehandwriting.activities.RoomActivity;
  
  import android.content.res.AssetManager;
  import android.os.Bundle;
  import android.app.Activity;
  import android.util.Log;
  import android.view.View;
  
  import com.github.barteksc.pdfviewer.PDFView;
  import com.github.barteksc.pdfviewer.listener.OnLoadCompleteListener;
  import com.github.barteksc.pdfviewer.listener.OnPageChangeListener;
  import com.github.barteksc.pdfviewer.scroll.DefaultScrollHandle;
  
  import group6.interactivehandwriting.R;
  import group6.interactivehandwriting.activities.RoomActivity.views.DocumentView;
  import group6.interactivehandwriting.activities.RoomActivity.views.RoomView;
  
  public class RoomActivity extends Activity implements OnPageChangeListener, OnLoadCompleteListener {
      RoomView roomView;
      DocumentView docView;
      PDFView pView;
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          Log.d("Android: ", "Setting content view to an instance of RoomView in: " + this.getClass().getName());
          setContentView(R.layout.activity_draw);
  
          System.out.println("Attempting to set ImageView..");
          pView = (PDFView) findViewById(R.id.pdfView);
          pView.fromAsset("sample.pdf").defaultPage(0)
                  .enableSwipe(true).swipeHorizontal(false).
                  onPageChange(this).enableAnnotationRendering(true).onLoad(this).scrollHandle(new DefaultScrollHandle(this)).load();
  
  
      }
  
      @Override
      public void onPageChanged(int page, int pageCount) {
          setTitle(String.format("%s %s / %s", "Sample", page + 1, pageCount));
      }
  
      @Override
      public void loadComplete(int nbPages) {
      }
  }
  

  AndroidManifest.xml

  <?xml version="1.0" encoding="utf-8"?>
  <manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="group6.interactivehandwriting">
  
      <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
      <application
          android:allowBackup="true"
          android:icon="@mipmap/ic_launcher"
          android:label="@string/app_name"
          android:roundIcon="@mipmap/ic_launcher_round"
          android:supportsRtl="true"
          android:theme="@style/AppTheme">
          <activity
              android:name=".activities.RoomActivity.RoomActivity"
              android:label="@string/title_activity_menu"
              android:theme="@style/AppTheme.NoActionBar">
              <intent-filter>
                  <action android:name="android.intent.action.MAIN" />
  
                  <category android:name="android.intent.category.LAUNCHER" />
              </intent-filter>
          </activity>
      </application>
  
  </manifest>
  

  activity_draw.xml

  <?xml version="1.0" encoding="utf-8"?>
  <android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:app="http://schemas.android.com/apk/res-auto"
      xmlns:tools="http://schemas.android.com/tools"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      tools:context=".activities.RoomActivity.RoomActivity">
  
      <view
          android:id="@+id/room_view"
          id="@+id/view"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          app:layout_constraintBottom_toBottomOf="parent"
          app:layout_constraintEnd_toEndOf="parent"
          app:layout_constraintStart_toStartOf="parent"
          app:layout_constraintTop_toTopOf="parent" />
  
      <com.github.barteksc.pdfviewer.PDFView
          android:id="@+id/pdfView"
          android:layout_width="match_parent"
          android:layout_height="match_parent"/>
  
      <TextView
          android:id="@+id/textView"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_marginStart="8dp"
          android:layout_marginTop="8dp"
          android:text="@string/room"
          app:layout_constraintStart_toStartOf="parent"
          app:layout_constraintTop_toTopOf="parent" />
  
  </android.support.constraint.ConstraintLayout>
  

  Dependencies:

  compile 'com.github.barteksc:android-pdf-viewer:2.8.2'
  
  compile 'org.apache.commons:commons-collections4:4.1'
  
• Consider defining a bean named 'entityManagerFactory' in your configuration.3

  I'm just following some tutorial how to upload documents via spring. So while working on it i faced above issue. Since there are many questions related to same question i refer them and tried everything but none corrected m problem. In advance i don't need to add @Repository for my Repository interface and @EnableJpaRepositories in my Application class as i have use correct package sequence. For more reference refer https://dzone.com/articles/spring-spring-boot-and-component-scan. Please help me out.

  Application class

  @SpringBootApplication
  @ComponentScan("com.project.abhishek")
  public class DocumnetwebApplication {
  
  public static void main(String[] args) {
      SpringApplication.run(DocumnetwebApplication.class, args);
  }}
  

  Controller

  @Controller
  public class DocumentController {
  
  @Autowired
  private DocumentRepository documentRepo;
  
  @RequestMapping("/displayUpload")
  public String displayUpload() {
      return "documentUpload";
  }
  
  @RequestMapping(value="/upload", method=RequestMethod.POST )
  public String upload(@RequestParam("document")MultipartFile multiPartFile, @RequestParam("id")long id) {
  
      Document document = new Document(); 
      document.setId(id);
      document.setName(multiPartFile.getName());
      try {
          document.setData(multiPartFile.getBytes());
      } catch (IOException e) {
          e.printStackTrace();
      }
      documentRepo.save(document);
  
      return "documentUpload";
  }}
  

  Bean

  @Entity
  public class Document {
  
  @Id
  private long id;
  private String name;
  @Lob
  private byte[] data;
  //getters and setters}}
  

  Repository

  public interface DocumentRepository extends JpaRepository<Document, Long> {}
  

  Application properties file

  spring.datasource.url=jdbc:mysql://localhost:3306/mydb
  spring.datasource.username=root
  spring.datasource.password=test
  spring.jpa.properties.hibernate.id.new_generator_mappings=false
  spring.jpa.show-sql=true
  server.port=8083
  spring.mvc.view.prefix=/WEB-INF/jsps/
  spring.mvc.view.suffix=.jsp
  server.servlet.context-path= /documentweb
  

  pom file

  <dependencies>
      <dependency>
          <groupId>org.springframework.boot</groupId>
          <artifactId>spring-boot-starter-data-jpa</artifactId>
      </dependency>
      <dependency>
          <groupId>org.springframework.boot</groupId>
          <artifactId>spring-boot-starter-web</artifactId>
      </dependency>
  
      <dependency>
          <groupId>mysql</groupId>
          <artifactId>mysql-connector-java</artifactId>
          <scope>runtime</scope>
      </dependency>
      <dependency>
          <groupId>org.springframework.boot</groupId>
          <artifactId>spring-boot-starter-test</artifactId>
          <scope>test</scope>
      </dependency>
      <dependency>
          <groupId>org.apache.tomcat.embed</groupId>
          <artifactId>tomcat-embed-jasper</artifactId>
          <version>9.0.12</version>
          <scope>provided</scope>
  
      </dependency>
      <dependency>
          <groupId>javax.servlet</groupId>
          <artifactId>jstl</artifactId>
      </dependency>
  
  </dependencies>
  

  Package Structure

  com.project.abhishek---application class  
  com.project.abhishek.controller  
  com.project.abhishek.entity  
  com.project.abhishek.repository
  
• Trying to fit the settings activity in a fragment window - Android Studio

  I am working on an app and something troubles me, I want to create a settings activity in a fragment layout and the thing is that if I create a settings activity from the android studio's menu (this), there's no way that I can transform it into a fragment. I want to make it be this way (photo) .

  The thing is that when i change fragments, i use theFragment = new fragment_body();, where it is public class fragment_body extends Fragment, with its onCreateView of:

  public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
          return inflater.inflate(R.layout.view_settings, null);
      }
  

  where on the settings activity i don't have any of these things, i've tried multiple things but i don't know how to do it. Where the settings activity is: public class SettingsActivity extends PreferenceActivity. Please guide me of how to do this, Thanks in advance.
• How do I write to an apache.poi.xssf Excel Worksheet faster?

  I am using jdbcTemplate to query to an ETL tool and fetch the results and write to an Excel Worksheet using Apache POI library. I have somewhere between 700,000 and 1,000,000 rows to fetch and write.

  Earlier I had the following setup:

  jdbcTemplate.query(new CustomPreparedStatementCreator(arg), new ResultSetExtractor<Void>() {
      @Override
      public Void extractData(ResultSet rs) {
      while (rs.next()) {... process sequentially ...}
      // caused the connection to remain open for 650 seconds
      // setFetchSize was not set so it was default
  }
  

  Now I have the following setup:

  jdbcTemplate.setFetchSize(200);
  SqlRowSet srs = jdbcTemplate.queryForRowSet(sql);
  // all the rows are fetched in 60 seconds into memory now
  while (srs.next()) {... process sequentially ...} // still takes 600 seconds to write to the worksheet
  

  Now my problems are:

  1. How to I leverage the Java 8 parallelStream API to process all the rows inside a SqlRowSet object? Is there any alternative?
  2. How can I write faster to the worksheet (an org.apache.poi.xssf.streaming.SXSSFSheet) ?
• restriction set by the accessExternalStylesheet property error

  I am getting below error.

  ERROR: 'java.lang.Exception: Could not read stylesheet target 'xxxxxxxx.xsl', because 'classpath' access is not allowed due to restriction set by the accessExternalStylesheet property.'

  I am trying to transform xml to html using xxxxxxxx.xsl but getting the above error.

  application.yml:

  trToHtmlXsl : classpath:/tr-transcripts.xsl
  

  same code runs for different xsl and transformations.
• Using lambda impedes inference of type variable

  I have the following code which compiles successfully:

  import java.lang.String;
  import java.util.List;
  import java.util.Arrays;
  
  interface Supplier<R> {
      Foo<R> get();
  }
  
  interface Foo<R> {
      public R getBar();
      public void init();  
  }
  
  public class Main {
  
      static private <V> void doSomething(final Supplier<? extends List<? extends V>> supplier) {
      // do something
      }
  
      static public void main(String[] args) {
          doSomething(new Supplier<List<Object>>(){
             @Override
             public Foo<List<Object>> get() {
                 return new Foo<List<Object>>(){
                     @Override
                     public List<Object> getBar() {
                         return null;
                     }
                     @Override
                     public void init() {
                        // initialisation
                     }
                 };
              }
         });
      }
  }
  

  However, if I convert the Supplier to the following lambda expression the code does not compile anymore:

  doSomething(() -> new Foo<List<Object>>(){
      @Override
      public List<Object> getBar() {
          return null;
      }
  });
  

  The compiler error is:

  Main.java:22: error: method doSomething in class Main cannot be applied to given types;
      doSomething(() -> new Foo<List<Object>>(){
      ^
    required: Supplier<? extends List<? extends V>>
    found: ()->new Fo[...]; } }
    reason: cannot infer type-variable(s) V
      (argument mismatch; bad return type in lambda expression
        <anonymous Foo<List<Object>>> cannot be converted to Foo<List<? extends V>>)
    where V is a type-variable:
      V extends Object declared in method <V>doSomething(Supplier<? extends List<? extends V>>)
  

  If I change the declaration of the supplier to Supplier<? extends List<V>>, both variants compile successfully.

  I compile the code with a Java 8 compiler.

  Why does the code with the lambda not compile, although it is equivalent to the non-lambda version? Is this a known/intended limitation of Java or is it a bug?
• Stream.sorted() then collect, or collect then List.sort()?

  In general, is there a performance difference between these two pieces of code?

  List<Integer> list1 = someStream1.sorted().collect(toList());
  // vs.
  List<Integer> list2 = someStream2.collect(toList());
  list2.sort(Comparator.naturalOrder())
  

  Variant 2 is obviously yucky and should be avoided, but I'm curious if there are any performance optimizations built into the mainstream (heh, mainstream) implementations of Stream that would result in a performance difference between these two.

  I imagine that because the stream has strictly more information about the situation, it would have a better opportunity to optimize. E.g. I imagine if this had a findFirst() call tacked on, it would elide the sort, in favor of a min operation.
• How to find max length in list of string using streams in Java?

  I have a class like below:

  public class A
  {
      String name;
      String getName(){return name;}
  }
  

  And I also have a list like below:

  List<A> list_a = new ArrayList<>();
  //add n objects into list_a
  

  Right now I would like to find the max length of object which is in list_a using streams in Java. I have created code like below:

  final int max_len = list_a.stream().max(Comparator.comparingInt(A::getName::length));
  

  But it does not work, I mean it is something bad with syntax. Could you help me with this? Thank you.
• Skip a same combination in Stream API

  I have a List filteredList where and I am streaming over each element and using for each to set some items

  filteredList.parallelStream().forEach(s->{
  
              ARChaic option=new ARChaic();
              option.setCpu(s.getNoOfCPU());
              option.setMem(s.getMemory());
              option.setStorage(s.getStorage());
              option.setOperatingSystem(s.getOperationSystem());
  
  
             ARChaic newOption= providerDes.getLatest(option); //this is a external service
          s.setCloudMemory(newOption.getMem());
          s.setCloudCPU(newOption.getCpu());
          s.setCloudStorage(newOption.getStorage());
          s.setCloudOS(newOption.getOperatingSystem());
  
  });
  

  The goal is to call this service but if the above option is same then take the old one to call.

  For Example- if two server have same memory,cpu,os and storage then it will call getLatest only once.

  Suppose at position 1 and 7 in filteredList I have same config then I shouldn't be calling getLatest again at 7 since I already have previous option value which I will set it 7(Working done after service call)