Active Ming Qin – ActiveMQ

Computing for embedded devices, tablets and computers

OAuth 2 Authorization Code Grant Type Client’s HTTP Basic Authorization Post Monitoring

  This post is started from a question posted at online forum of the book << OAuth 2 in Action>>.  In that case of  OAuth 2 authorization code grant type implementation,  the OAuth 2 confidential client ( client.js -a server side node.js process ) performs an HTTP  POST with its parameters as a form-encoded HTTP entity body, passing its client_id and client_secret as an HTTP Basic authorization header. This is the beauty of security of authorization code type means the HTTP request is made directly between the client ( client.js ) and the authorization server, without exposing HTTP Basic authorization userid and password information to the browser or resource owner at all.

  Unfortunately,client.js’s HTTP post of Basic authorization is running based on local loopback network,  Wireshark and Fiddler tools failed on capturing this HTTP session information. After a few attempts,  the author finds Microsoft Message Analyzer can do the trick by employing  Local Loopback Network scenario.   Here are the online training videos of Microsoft Message Analyzer. Enjoy!

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Spring-boot Security(1.5.4 release) – Support Cross Site Scripting (XSS) Protection

By reading this post and practicing the sample application, readers can understand Spring Boot’s security on supporting cross site scripting (xss), and how to turn on/off  X-XSS-Protection header when starting a Spring-Boot application which is in conjunction with WebSecurityConfigurerAdapter.

Spring-Boot xss supporting means APIs could set up header X-XSS-Protection in HTTP response header which is utilized by web browsers to prevent reflected cross-scripting attacks, known as the XSS Filter.   EricLaw wrote a nice article covered about XSS Filter which provided a vivid example of web form submitting of this kind of XSS attack.

Spring-Boot’s subproject -Spring Boot AutoConfigure (main branch and v2.0.0.M2 tag) source codes on GitHub showed JUnit test codes to enable and turn on/off X-XSS-Protection header.  The class name is SpringBootWebSecurityConfigurationTests.java and two method names are testWebConfigurationOverrideGlobalAuthentication() and securityHeadersCanBeDisabled(), just pay attend to code snippets contains X-XSS-Protection.

If JUnit test codes in Source codes are not good enough, I wrote a simple Spring Boot application which cam demo how to enable, turn on/turn off X-XSS-Protection.  The codes are in at X-XSS-Protection branch of  GitHub project.


import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.autoconfigure.security.SecurityProperties;
import org.springframework.boot.builder.SpringApplicationBuilder;
import org.springframework.core.annotation.Order;
import org.springframework.security.config.annotation.authentication.builders.AuthenticationManagerBuilder;
import org.springframework.security.config.annotation.web.builders.HttpSecurity;
import org.springframework.security.config.annotation.web.configuration.EnableWebSecurity;
import org.springframework.security.config.annotation.web.configuration.WebSecurityConfigurerAdapter;

@SpringBootApplication
@EnableWebSecurity
//@Order(ManagementServerProperties.ACCESS_OVERRIDE_ORDER)
@Order(SecurityProperties.ACCESS_OVERRIDE_ORDER)
public class DemoApplication extends WebSecurityConfigurerAdapter {

public static void main(String[] args) {
new SpringApplicationBuilder(DemoApplication.class)
.properties("management.context-path:/actuator").run(args);
}

@Override
protected void configure(AuthenticationManagerBuilder auth) throws Exception {
auth.inMemoryAuthentication().withUser("admin").password("secret").roles("ACTUATOR");
}

@Override
protected void configure(HttpSecurity http) throws Exception {

http.headers().xssProtection().disable();

}

}

To test the code, I entered URL as http://localhost:8080/actuator/metrics in Chrome Extension Postman to observe whether X-XSS-Protection being enabled or turned on./off.

When using Order(SecurityProperties.ACCESS_OVERRIDE_ORDER) and overriding configure (HttpSecurity HTTP) method, X-XSS-Protection header can be programmatically changed.

But using @Order(ManagementServerProperties.ACCESS_OVERRIDE_ORDER), the same effect of enabling X-XSS-Protection can be achieved through the application.properties file’s configuration value on attribute name as security.headers.xss

Spring-boot Security(1.5.4 release) – Actuator Security , Form-based login and Basic Auth login

By reading this post and practicing the sample application, readers can get an insight of Spring-boot Security authentication mechanism which would be helpful to expand customized Spring-boot authentication component to secure endpoints.

Spring-boot actuator offers management endpoints to monitor spring-boot based application. The most used management endpoints of Actuator are health and metrics. Like all the application endpoints in a spring-boot application, the proper user authentication mechanism needs to be applied to that kind of endpoints as well, which leads a concept in term of Actuator Security in the document as following statements in the section of Spring-boot Security:

  If the Actuator is also in use, you will find:

  • The management endpoints are secure even if the application endpoints are insecure.
  • Security events are transformed into AuditEvent instances and published to the AuditEventRepository.
  • The default user will have the ACTUATOR role as well as the USER role.

The Actuator security features can be modified using external properties (management.security.*). To override the application access rules add a @Bean of type WebSecurityConfigurerAdapter and
use @Order(SecurityProperties.ACCESS_OVERRIDE_ORDER) if you don’t want to override the actuator access rules,
or
@Order(ManagementServerProperties.ACCESS_OVERRIDE_ORDER) if you do want to override the actuator access rules.

Andy Wilkison posted a code snippet to demo the usage WebesecurityConfiguerAdapter and annotations( @EnableWebSecurity and @Order(ManagementServerProperties.ACCESS_OVERRIDE_ORDER) to override Actuator Access Rules.

I cloned and modified his codes to figure out what are the user authentication mechanisms being employed respectively with annotations @Order(SecurityProperties.ACCESS_OVERRIDE_ORDER) and @Order(ManagementServerProperties.ACCESS_OVERRIDE_ORDER)

 

To test the code, I entered URL as http://localhost:8080/actuator/metrics in Chrome browser and modified chrome setting as settings-> advanced->System -> Continue running background apps when Google Chrome is closed ( to be turned off). And closing old chrome browser and open a fresh new one to test each case.

When enabling  @EnableWebSecurity  and @Order(ManagementServerProperties.ACCESS_OVERRIDE_ORDER),  actuator metrics endpoint is secured by form-based user authentication. User id and password are defined in method configure(AuthenticationManagerBuilder auth). Also,  a cookie JESSIONID is created.

 

When  enabling  @EnableWebSecurity  and @Order(SecurityProperties.ACCESS_OVERRIDE_ORDER),  actuator metrics endpoint is secured by http basic authentication. User id ( user) and password are defined in  static class DefaultInMemoryUserDetailsManagerConfigurer of org.springframework.boot.autoconfigure.security.AuthenticationManagerConfiguration.java

The password ( in the format of  xxxxxx-xxxx-xxxx-xxxx-xxxxxxxx )can be contained from a console print by searching phrase “Using default security password:” which will be changed every time the application gets rebooted.

 

We can add following codes into DemoApplication.java , then test URL http://localhost:8080/actuator/metrics again .


@Override
protected void configure(HttpSecurity http) throws Exception {
BasicAuthenticationEntryPoint authenticationEntryPoint = new BasicAuthenticationEntryPoint();
authenticationEntryPoint.setRealmName("example");
http.httpBasic().authenticationEntryPoint(authenticationEntryPoint);
http.authorizeRequests().antMatchers("/actuator").denyAll();
}

 

Following are codes being used for testing. The maven project source codes are in main branch of Github

package com.example;

import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.autoconfigure.security.SecurityProperties;
import org.springframework.boot.builder.SpringApplicationBuilder;
import org.springframework.core.annotation.Order;
import org.springframework.security.config.annotation.authentication.builders.AuthenticationManagerBuilder;
import org.springframework.security.config.annotation.web.configuration.EnableWebSecurity;
import org.springframework.security.config.annotation.web.configuration.WebSecurityConfigurerAdapter;

@SpringBootApplication
@EnableWebSecurity
//@Order(ManagementServerProperties.ACCESS_OVERRIDE_ORDER)
@Order(SecurityProperties.ACCESS_OVERRIDE_ORDER)
public class DemoApplication extends WebSecurityConfigurerAdapter {

public static void main(String[] args) {
new SpringApplicationBuilder(DemoApplication.class)
.properties("management.context-path:/actuator").run(args);
}

@Override
protected void configure(AuthenticationManagerBuilder auth) throws Exception {
auth.inMemoryAuthentication().withUser("admin").password("secret").roles("ACTUATOR");
}

}

Java 8 Stream Pitfall- Not Step Twice into the Same Stream

“You could not step twice into the same water”-Heraclitus of Ephesus

  A Stream does not store its elements.

I got caught by Stream’s not storing its elements.  My code created a Stream object  for type String. After evaluation of the emptiness of Stream object, that object is  “vanished” which throws exception as “stream has already been operated  upon or closed” if that Stream object is referenced again.

public static void main ( String[] args) throws Throwable {
   String input="usa_ca-culvercity";
   //words object is created.
   Stream<String> words = Stream.of(input.trim().split("[_-]")).skip(1);
   // words object is referenced  first time.
   if ( words.count()==0)  { throw new Exception(" input formatting is wrong  "+ input); }
   else{
   // words object could not be referenced anymore.
   // code throws exception
   //in thread "main" java.lang.IllegalStateException: <strong>stream has already been operated upon or closed</strong>
      System.out.println ( (String)  words.toArray()[0]);
   }
 } 

Lambda Expression-Using Function as first-class Member of Java to Detect Recurrence Value inside An Array

I find the best words to explain of Lambda from Oracle Lambda Quick Star web page. Here it is “Lambda expressions provide a clear and concise way to represent one method interface using an expression. Lambda expressions also improve the Collection libraries making it easier to iterate through, filter, and extract data from a Collection. In addition, new concurrency features improve performance in multicore environments.”

This blog is about my coding practice on using Lambda Express  to find recurrence value in an array of integer.

The problem is to figure out the number of recurrence value in an array of integer, which is bigger or equal to the half of length of that array.

Below code snippet shows a solution without utilizing Lambda Expression. The code sorts the array in ascending order, then compare the equality of next two elements in the array to the last element in there. There are two basic operations in this solution- measure equality of two integers and looping through the array.

import java.io.IOException;
import java.util.Arrays;
import java.util.Comparator;
import java.util.function.BiPredicate;

/**
 *
 * @author MingQin
 */
public class RecurrenceIntValueInArray {

    public static void main(String[] args) throws IOException {
        Integer[] ia = new Integer[]{1, 1, 6, 6, 8, 5, 7, 6, 6, 6};

        Arrays.sort(ia);
        System.out.println(" inputArray size : " + ia.length);
        int benchMark = ia.length / 2;
        int recurrenceCount = 1;
        
        for (int i = 0; i < ia.length - 1; i++) {             
                   if (ia[i].equals(ia[i+1])) {               
                         recurrenceCount++;                
                         if (recurrenceCount >= benchMark) {
                    break;
                }
            } else {
                recurrenceCount = 1;
          // replacing above line to return-1, the ia array will be stored
          // in descending order

            }

        }//end for 
        if (recurrenceCount >= benchMark) {
            System.out.println(" Yes :  " + (recurrenceCount));
        } else {
            System.out.println(" No");
        }

    }//end main

}


I want to use Lambda Expression to replace those two operations. First starting point is working on operation of the equality of two integers.

Since a lambda expression can be a substitute of Function Interface, if a Function Interface provides abstract method to take two type parameters as inputs and return another type, then they are pretty good to be considered. Comparator and BiPredicate function interface are merged.

import java.io.IOException;
import java.util.Arrays;
import java.util.Comparator;
import java.util.function.BiPredicate;

/**
 *
 * @author MingQin
 */
public class RecurrenceIntValueInArray {

    public static void main(String[] args) throws IOException {
        Integer[] ia = new Integer[]{1, 1, 6, 6, 8, 5, 7, 6, 6, 6};

        Arrays.sort(ia);
        System.out.println(" inputArray size : " + ia.length);
        int benchMark = ia.length / 2;
        int recurrenceCount = 1;
         //Comparator Lambda Expression
        recurrenceCount = 1;
        Comparator<Integer> comp = 
        (first, second) -> Integer.compare(first.intValue(),second.intValue());
        for (int i = 0; i < ia.length - 1; i++) {             
               int result = comp.compare(ia[i], ia[i + 1]);            
               recurrenceCount = (result == 0) ? recurrenceCount + 1 : 1;           
               if (recurrenceCount >= benchMark) {
                break;
            }

        }//end for 

        if (recurrenceCount >= benchMark) {
            System.out.println(" Yes :  " + (recurrenceCount));
        } else {
            System.out.println(" No");
        }

        //BiPrdicate Lambda Expression
        recurrenceCount = 1;
        BiPredicate<Integer, Integer> biPredicate = (x, y) -> x.equals(y);
        for (int i = 0; i < ia.length - 1; i++) {           
                 boolean result = biPredicate.test(ia[i], ia[i + 1]);            
                 recurrenceCount = (result) ? recurrenceCount + 1 : 1;           
                 if (recurrenceCount >= benchMark) {
                break;
            }

        }//end for 
        if (recurrenceCount >= benchMark) {
            System.out.println(" Yes :  " + (recurrenceCount));
        } else {
            System.out.println(" No");
        }
        

    }//end main

}

Now, I come to the last task replacing for loop with Lambda Express. The approach is using a Lambda Expression as an instance of Comparator Function Interface in Arrays.sort( T[] a , Comparator<? Super T> c).

import java.io.IOException;
import java.util.Arrays;
import java.util.Comparator;
import java.util.function.BiPredicate;

/**
 *
 * @author Ming Qin
 */
public class RecurrenceIntValueInArrayLambda {

    public static void main(String[] args) throws IOException {
        Integer[] ia = new Integer[]{1, 1, 6, 6, 8, 5, 7, 6, 6, 6};

        Arrays.sort(ia);
        System.out.println(" inputArray size : " + ia.length);
        int benchMark = ia.length / 2;
        
        final int[] count = new int[1];
        count[0] = 1;
        BiPredicate<Integer, Integer> biPredicate = (x, y) -> x.equals(y);
    
        Arrays.sort(ia, (tail, head) -> {
            boolean result = biPredicate.test(head, tail);
            if (result) {
                count[0]++;
            } else {
                count[0] = 1;
            }
            System.out.println(" ++++++++++  :" + count[0] + " head : " + head
                    + "  tail:" + tail);
            if (count[0] >= benchMark) {
                System.out.println(" Yes :  " + count[0]);       
            }
            return count[0];
        });
    }//end main
}

Coming back the statement of Lambda Expression  definition-
Lambda expressions also improve the Collection libraries making it easier to iterate through, filter,
and extract data from a Collection

Ha, Is above statement meaning that I could utilize Stream API and filter method for another solution?

What a journey.


import java.io.IOException;
import java.util.Arrays;
import java.util.List;
import java.util.Set;
import java.util.Optional;
import java.util.stream.Collectors;
/**
 *
 * @author mqin
 */
public class RecurrenceIntValueInArrayLambda {

    public static void main(String[] args) throws IOException {
        Integer[] ia = new Integer[]{1, 1, 6, 6, 8, 5, 7, 6, 6, 6};
        List<Integer> ilist = Arrays.asList(ia);

        Optional<Integer> result0= ilist.stream().filter(
                    x->ilist.stream().filter (
                         y->y.equals(x)
                       ).count()>=ia.length/2
                   ).findFirst();
        if ( result0.isPresent()) System.out.println ( "Yes, it is " + result.get());


// another stream solution.        
         
        Set<Integer> result = ilist.stream().filter(x -> ilist.stream().filter(
                y -> y.equals(x)).count() >= ia.length / 2
        ).collect(Collectors.toSet());
        
        if (!result.isEmpty()) System.out.println ( "Yes");

    }//end main

}


Apache Avro IDL Composes Avro Schema by AvroHubTools

                        Simple is better than complex

Nowadays, data storage cost is cheap ( almost free),  but data bandwidth is costly( thinking about monthly fees paid towards smart phone data transfer and house internet access). As more and more things ( watch, refrigerator , car, etc) are connected to each other through internet,  the online traffic could be notorious analogy to freeway 405 in Great Los Angeles.   Apache Avro can be helpful on this situation with its compact binary data representation since avro data size is much less verbose than  text-based XML or JSON.

In another blog, I mentioned the usage of Apache Avro schema to model data as replacement of XML and JSON. After that, I developed AvroHubTools to author Avro schema by Apache Avro IDL. In this blog, I will try to demonstrate employing Avro IDL to generate Avro schema in conjunction with AvroHubTools, in below topics:

  •   How to encapsulate Avro schemas and build standalone scheme out of multiple, external and independent  Avro schema files.
  •   How to reuse Avro schemas through inheritance.
  •   How to apply polymorphism in data modeling by Avro schemas.

AvroHubTools ( obf-avro-hub-tools-1.0-SNAPSHOT.jar) can be downloaded from this link and has been tested with JDK 1.6.45 and Apache Avro 1.7.7 release.  AvroHubTools can support other Apache Avro versions, please make request by leaving comments on this blog.

Encapsulating ( data hiding)  with Apache Avro Schemas

Encapsulation in here means the packing of date into a single Avro Schema. Let’s assume ones like to model data in Avro scheme about baseball team.  We get player, play position, coach as components , as well as name since player and coach reference name component.  A play can be assigned to multiple coaches.   baseball.avdl Avro IDL to pack four Avro schema files in order to generate Team.avsc

baseball.avdl is defined as below.

@namespace("avro.examples.baseball")
protocol Baseball {
   import schema "name.avsc";
   import schema "coache.avsc";
   import schema "position.avsc";
   import schema "player.avsc";
  
   record Team {
      
       Player player;
       Coache  coache;
         
  }
}

Below are team Avro schema components: name.avsc, position.avsc, coache.avsc and play.avsc

name.avsc

{"type":"record", "name":"Name", "namespace": "avro.examples.baseball",
  "fields": [
   {"name": "first_name", "type": "string"},
   {"name": "last_name", "type": "string"}
  ]
}

position.avsc

{"type":"enum", "name": "Position", "namespace": "avro.examples.baseball",
    "symbols": ["P", "C", "B1", "B2", "B3", "SS", "LF", "CF", "RF", "DH"]
}

coache.avsc

{"type":"record", "name":"Coache", "namespace": "avro.examples.baseball",
  "fields": [
   {"name": "name", "type": "Name"}
 
  ]
}

play.avsc

<pre>{"type":"record", "name":"Player", "namespace": "avro.examples.baseball",
  "fields": [
   {"name": "number", "type": "int"},
   {"name": "name", "type": "Name"},
   {"name": "positions", "type": {"type": "array", "items": "Position"} },
   {"name": "coaches", "type": {"type": "array", "items": "Coache"} }
  ]
}

To generate Team.avsc, run below line by utilizing AvroHubTools.
java -jar obf-avro-hub-tools-1.0-SNAPSHOT.jar   idlavsc   baseball.avdl avro.examples.baseball.Team   baseballTeam.avsc

Here is generated baseballTeam.avse

{
  "type" : "record",
  "name" : "Team",
  "namespace" : "avro.examples.baseball",
  "fields" : [ {
    "name" : "player",
    "type" : {
      "type" : "record",
      "name" : "Player",
      "fields" : [ {
        "name" : "number",
        "type" : "int"
      }, {
        "name" : "name",
        "type" : {
          "type" : "record",
          "name" : "Name",
          "fields" : [ {
            "name" : "first_name",
            "type" : "string"
          }, {
            "name" : "last_name",
            "type" : "string"
          } ]
        }
      }, {
        "name" : "positions",
        "type" : {
          "type" : "array",
          "items" : {
            "type" : "enum",
            "name" : "Position",
            "symbols" : [ "P", "C", "B1", "B2", "B3", "SS", "LF", "CF", "RF", "DH" ]
          }
        }
      }, {
        "name" : "coaches",
        "type" : {
          "type" : "array",
          "items" : {
            "type" : "record",
            "name" : "Coache",
            "fields" : [ {
              "name" : "name",
              "type" : "Name"
            } ]
          }
        }
      } ]
    }
  }, {
    "name" : "coache",
    "type" : "Coache"
  } ]
}

To Be Continued……..

Apache Avro Object Container File Format Examination-Header

Understating is more important than technique

First to me,  apache avro is a file storage mechanism can be used for NOSQL data storage as well as an alternative binary data representation in replacement of text XML or JSON (  avro schema and idl-avsc,avdl VS xsd, avro object container file VS xml) for enterprise computing, mobile device, embedded linux motherboard or  SOA data inter-exchange .

After reading the apache avro Spec of Object Container File, I decided to generate an avro object container file ( Header and Blocks) to understand its binary content layout. Below picture depicts the overall avro object container file  binary structure.  I  drill down the only header portion of it.

avro object container file format

Apache Avro -1.8.0-SNAPSHOT source codes ware loaded into Netbean 8.o on CentOS-6.4 hosted by VMWare Workstation 11 running on window 8.1

My avro schema named as legopiece.avsc which was defined as below snippet .

   {
    "namespace":"com.example.avroSample.model",
    "type":"record",
    "name":"LegoPiece",
    "fields":[
        {
            "name":"modelName",
            "type":"string"
        },
        {
            "name":"modelYear",
            "type":"int"
        },
        {
            "name":"stubNumber",
            "type":"string"
        }   
    ]   
}

Below codes are used to generate an avro object container file- legopieoce.avro which describes a  lego brick has two stubs, model year is 2147483647( java max int positive number), model name is Brick 1×2 Green (15-character length text).

green brick two stubs

......
       private static final File outputFile = new File("target/avro/legopiece.avro");
       LegoPiece legoPiece = LegoPiece.newBuilder()
                .setModelName("Brick 1X2 Green").setModelYear(2147483647)
                .setStubNumber("2").build();
                               
        DatumWriter<LegoPiece> datumWriter = new SpecificDatumWriter<LegoPiece>(
                LegoPiece.class);
        DataFileWriter<LegoPiece> fileWriter = new DataFileWriter<LegoPiece>(
                datumWriter);
        try {
            // creating legopieice.avro -object container file for containing
            // binary format of legoPiece object
            fileWriter.create(legoPiece.getSchema(), outputFile);
            fileWriter.append(legoPiece);
            fileWriter.close();
        } catch (IOException e) {
            LOGGER.error("Error while trying to write the object to file <"
                    + outputFile.getAbsolutePath() + ">.", e);
        }
....

Here is the picture of legopiece.avro displayed in Hex Editor Neo( window version).

CaptureAvroLegoPiece

It is the time to turn on the java debugger and go through codes in maven sub model named as “Apache Avro”  to figure out how those bytes  were written to legopiece.avro  .

DataFileWriter

A few breakpoints were set up inside DataFileWriter.java‘s method DataFileWriter<D> create(Schema, OutputStream outs).  This method made bytes representing following items of object container file header:

  • Four bytes,  ‘O’, ‘b’, ‘j’ , followed by  ‘1’  – referencing legopiece.avro’s Hex layout picture, we could find  the corresponding first four bytes as UTF-8 codes of  4f , 62, 6a , 01. Here is UTF-8 codepage layout to  help understanding UTF-8 code’s matching characters.
  • File metadata, including the schema and their values’ lengths being measured in int values using firstly  zig-zag,  secondly  variable-length coding

    public static int encodeInt(int n, byte[] buf, int pos) {
    // move sign to low-order bit, and flip others if negative
    n = (n << 1) ^ (n >> 31);
    int start = pos;
    if ((n & ~0x7F) != 0) {
     buf[pos++] = (byte)((n | 0x80) & 0xFF);
     n >>>= 7;
      if (n > 0x7F) {
        buf[pos++] = (byte)((n | 0x80) & 0xFF);
        n >>>= 7;
        if (n > 0x7F) {
          buf[pos++] = (byte)((n | 0x80) & 0xFF);
          n >>>= 7;
          if (n > 0x7F) {
          buf[pos++] = (byte)((n | 0x80) & 0xFF);
          n >>>= 7;
         }
        }
      }
    }
    buf[pos++] = (byte) n;
    return pos - start;
    }
    
  • The 16-type , randomly-generated sync marker for legopiece.avro

AvroLegoPieceHeader

If  someones like to figure out how blocks portion of legopiece.avro are generated. Method of void writeBlockTo(BinaryEncoder e, byte[] sync) throws IOException  inside DataFilesStream.java is worth exploring.

Next Post: Apache Avro IDL Compose Avro Schema By AvroHubTool

RESOURCES:

What is Apache Avro?

Apache Avro’s starter Doug Cutting had a video on this blog could tell the purpose of Avro. For the impatient,  to start listening at 8 minutes of the video.

Java 8 Stream API measured By JMH-Java Microbenchmark Harness

From my studying on the new features of Java 8, such as declarative style programming , functional programming,   default method and  lambda expression,   I would say those new features are all designed  for centrally supporting parallelism Stream API.   To master Java 8,  ones must get good understanding about Stream API.

Java 8 claimed that Stream API would employ multi-core CPUs  to process data in parallel fashion which would eliminate difficulties  of  dealing with multi-thread  codes , as well as gaining performance advantages obtained from  multicored CPUs.

As we all knew  that Stream API would cause some overhead associated with java thread pool and Fork-Join programming paradigm.  Developers need a handy tool to scrutinize and rationalize the adopting Stream API on daily coding task, in order to validate whether performance enhancement is obtained .  JMH seems a handy one for this purpose.  Watching this video for the insight of JMH.

I created   a JMH( version 1.3.3)  maven project with  a class JMHSample_01_HelloWorld to measure the throughputs of getting sum of integer addition in four fashions: foo loop, iteration , Stream parallel and Stream sequential.  From the outputs generated by running this command from Window console

java -jar target/benchmarks.jar JMHSample_01 -wi 5 -t 1 -i 5 -f 1

Stream parallel one is the slowest one among four approaches of summing  integers in array.

Benchmark                 Mode  Samples   Score       Error  Units
parallelSumIntegers    thrpt        5         26.902 ▒ 3.997  ops/s

Attached with screenshot of all four JMH measured results.

jmh_result

My machine is installed with Window 8.1 64 bit operating System ;processor is Intel(R) Core(TM) i7-4500U CPU having 4 cores ; RAM is 16 GB; JDK : Oracle 1.8u25-windows-x64.

Below section lists codes to generate above results.

package org.sample;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.concurrent.TimeUnit;
import org.openjdk.jmh.annotations.Benchmark;
import org.openjdk.jmh.annotations.BenchmarkMode;
import org.openjdk.jmh.annotations.Mode;
import org.openjdk.jmh.annotations.OutputTimeUnit;
import org.openjdk.jmh.annotations.Scope;
import org.openjdk.jmh.annotations.Setup;
import org.openjdk.jmh.annotations.State;
import org.openjdk.jmh.runner.Runner;
import org.openjdk.jmh.runner.RunnerException;
import org.openjdk.jmh.runner.options.Options;
import org.openjdk.jmh.runner.options.OptionsBuilder;

@State(Scope.Benchmark)
public class JMHSample_01_HelloWorld {
   volatile int counts = 9999999;
   volatile List<Integer> values = new ArrayList<>(counts);
   volatile int processors = Runtime.getRuntime().availableProcessors();

@Setup
public void setup() {
    populate(values);
}

public  void populate ( List<Integer>  list){
  for ( int i=0; i<counts ; i++){
       if ( i < counts/2){
         list.add(i, i );
       }else {
         list.add (i, i-counts);
      }
   }

}

@Benchmark
@BenchmarkMode(Mode.Throughput)
@OutputTimeUnit(TimeUnit.SECONDS)
public int iteratorSumIntegers(){
   int result =0;
   Iterator ite = values.iterator();
   while ( ite.hasNext()){
     result += (int)ite.next();
    }

   return result;
}

@Benchmark
@BenchmarkMode(Mode.Throughput)
@OutputTimeUnit(TimeUnit.SECONDS)
public int fooEachSumIntegers(){
   int result =0;
   for (Integer value :values) {
       result += value.intValue();
    }
    return result;
}

@Benchmark
@BenchmarkMode(Mode.Throughput)
@OutputTimeUnit(TimeUnit.SECONDS)
public int parallelSumIntegers( ){
   int result = values.parallelStream()
       .mapToInt(i->i)
       .sum();

       return result;

}

@Benchmark
@BenchmarkMode(Mode.Throughput)
@OutputTimeUnit(TimeUnit.SECONDS)
public int sequentialSumIntegers( ){
    int result = values.stream()
         .mapToInt(i->i)
         .sum();

        return result;

}

public static void main(String[] args) throws RunnerException {

  Options opt = new OptionsBuilder()
          .include(JMHSample_01_HelloWorld.class.getSimpleName())
          .forks(1)
          .build();

          new Runner(opt).run();
}

}

AngularJS scope API ($watch) and directives to implement Cascading Dropdown

Cascading drop-downs  are a hierarchical   ( parent-children ) relationship exists among multiple html drop-down components. When I try to implement cascading dropdown with AngularJS,  it is intuitive to me to depict that  the data representation of model is dynamically changed by events of selections( clickings). This impression leads me to give the first attempt of implementation with AngularJS scope ($watch) API, since ($watch) API is utilized by scope to observe model mutations.

Below codes illustrate scope watch API implementation on three-tier dropdowns. Top one is countries dropdown, middle one is states dropdown, and last one is cities dropdown.

<html>
    <head>
        <meta charset="UTF-8">
        <title>Cascading Dropdowns by Scope Watch</title>
        <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/angularjs/1.3.5/angular.min.js"></script>
    </head>
    <body ng-app="cascadingDropListApp">

        <div  ng-controller="CountryController" >
            <div>
                Country:
                <select id="country" ng-model="country" ng-options="country for country in countries">
                    <option value=''>Select</option>
                </select>
            </div>
            <div>
                City:
                <select id="state" ng-disabled="!states" ng-model="state" ng-options="state for state in states">
                    <option value=''>Select</option>
                </select>
            </div>
            <div>
                Suburb:
                <select id="city" ng-disabled="!cities" ng-model="city" ng-options="city for city in cities">
                    <option value=''>Select</option>
                </select>

            </div>

        </div>
            <script>
                        angular.module('cascadingDropListApp', [])
                                .controller('CountryController', ['$scope', function ($scope) {
                                        $scope.countries = ['china', 'united states'];
                                        $scope.$watch('country', function (newVal) {
                                            if (newVal ==='china')
                                                $scope.states = ['BeiJing', 'ShangHai'];
                                            if (newVal ==='united states')
                                                $scope.states = ['California', 'Mississippi'];
                                        });
                                        $scope.$watch('state', function (newVal) {
                                            if (newVal=== 'ShangHai')
                                                $scope.cities = ['JiaDing', 'HongQian', 'PuDong'];
                                            if (newVal=== 'BeiJing')
                                                $scope.cities = ['HaiDian', 'TianAnMen'];
                                            if (newVal=== 'California')
                                                $scope.cities = ['Los Angeles', 'Santa Barbara'];
                                            if (newVal=== 'Mississippi')
                                                $scope.cities = ['Jackson', 'Oxford'];
                                        });

                                    }]);

            </script>
    </body>
</html>

There is another pure directives implementation without involving scope watch API, it is shown in below.


<html>
<head>
<meta charset="UTF-8">
<title>Cascading Dropdowns </title>
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/angularjs/1.3.5/angular.min.js"></script>
</head>
<body ng-app="cascadingDropListApp">

<div  ng-controller="CountryController" >
<div>
Country:
<select id="country" ng-model="states" ng-options="country for (country, states) in countries">
<option value=''>Select</option>
</select>
</div>
<div>
States: <select id="state" ng-disabled="!states" ng-model="cities" ng-options="state for (state,cities) in states"><option value=''>Select</option></select>
</div>
<div>
City: <select id="city" ng-disabled="!cities || !states" ng-model="city" ng-options="city for city in cities"><option value=''>Select</option></select>
</div>
</div>

<script>
angular.module('cascadingDropListApp', [])
.controller ('CountryController', ['$scope', function($scope) {
$scope.countries = {
'China': {
'BeiJing': ['HaiDian', 'TianAnMen' ],
'ShangHai': ['JiaDing', 'HongQiao','PuDong']

},
'USA': {
'California': ['Los Angeles', 'Santa Barbara'],
'Mississippi': ['Jackson', 'Oxford']
}
};
}]);
</script>
</body>
</html>

Angular Scope events propagation and scope hierarchies are most valuable features
to pay a great attentions.

Object Oriented JavaScript( OOJS) Function Constructor to Demonstrate JavaScript Variable Lexical Scope

Javascript adopts Lexical Scope for variables’ defining and looking up.  The Lexical Scope means the variables are not determined  dynamically at runtime, rather they are defined and resolved as code blocks being written, top-down in place.

Let us take a look below codes which shows JavaScript Engine ( Java 8 Nashorn ) implementation of Lexical Scope on variables ( mirroring_a  and mirrored_a).


function foo( parameterA ) {
   //private member, viriable declaration
   var mirroring_a;
   //private member, variable declaration and assignment
   var mirrored={
       mirrored_a : mirroring_a  // undefined.  due to lexical scope, mirrored_a
                                 // failed to find variable mirroring_a
   };
   
   //public methods
   this.getMirroring_A = function () {
       return mirroring_a;
   };
   
   this.setMirroring_A = function ( newA ) {
       mirroring_a= newA;
   };
   
   this.getMirrored = function () {
       return mirrored;
   };
   // constructor code ,  assign parameter to variable mirroring_a
   this.setMirroring_A( parameterA);
   
   
 }
 
 var objFoo = new foo (  10);
 
for (var prop in  objFoo.getMirrored()) {
    if (prop === 'mirrored_a') {
        print(prop + '=  ' + objFoo.getMirrored()[prop]);
    }
   
}
 

objFoo.getMirrored()['mirrored-a']=777;

print (  objFoo.getMirrored()['mirrored-a'] );

print ( objFoo.getMirroring_A());

Result of running above snippet codes:
mirrored_a=  undefined
777
10
BUILD SUCCESSFUL (total time: 0 seconds)

 

Let me move the block code after constructor codes  – this.setMirroring_A( parameterA).


function foo( parameterA ) {
   //private member, variable declaration
   var mirroring_a;
   
   
   //public methods
   this.getMirroring_A = function () {
       return mirroring_a;
   };
   
   this.setMirroring_A = function ( newA ) {
       mirroring_a= newA;
   };
   
   this.getMirrored = function () {
       return mirrored;
   };
   // constructor code ,  assign parameter to variable mirroring_a
   this.setMirroring_A( parameterA);
   
   
    //private member, variable declaration and assignment
   var mirrored={
       mirrored_a : mirroring_a  // 10
   };
   
 
   
   
 }
 
 var objFoo = new foo (  10);
 

for (var prop in  objFoo.getMirrored()) {
    if (prop === 'mirrored_a') {
        print(prop + '=  ' + objFoo.getMirrored()[prop]);
    }
   
}
 

objFoo.getMirrored()['mirrored-a']=777;

print (  objFoo.getMirrored()['mirrored-a'] );

print ( objFoo.getMirroring_A());

Here are outputs above codes
mirrored_a=  10
777
10
BUILD SUCCESSFUL (total time: 0 seconds)