Java Security Notes
Java Security
well-behaved: programs should be prevent from consuming too much system resources
Components
- JCE: Java Cryptography Extension
- JSSE: Java Secure Socketets Extension
- JAAS: Java Authentication and Authorization Service
Anatomy of a Java Application
the bytecode verifier
The bytecode verifier ensures that Java class files follow the rules of the Java language. As the figure implies, not all classes are subject to bytecode verification.
the class loader
One or more class loaders load all Java classes. Programatically, the class loader can set permissions for each class it loads.
the access controller
The access controller allows (or prevents) most access from the core API to the operating system, based upon policies set by the end user or system administrator.
the security manager
The security manager is the primary interface between the core API and the operating system; it has the ultimate responsibility for allowing or preventing access to all system resources. However, it exists mostly for historical reasons; it defers its actions to the access controller.
The security package
the security package is a complex API. This includes discussions of:
- The security provider interface −− the means by which different security implementations may be plugged into the security package
- Message digests
- Keys and certificates
- Digital signatures
- Encryption (through JCE and JSSE)
- Authentication (through JAAS)
The key database
The key database is a set of keys used by the security infrastructure to create or verify digital signatures. In the Java architecture, it is part of the security package, though it may be manifested as an external file or database.
Trusted and Untrusted Classes
- In Java 2, only classes in the core API are considered trusted. Other classes must be given explicit permission to perform the operations we’ve discussed.
Summary
Although the security manager is the most commonly known feature of Java’s security story, it’s often misunderstood: there is no standard security manager among Java implementations, and Java applications, by default, have no security manager at all.
Access Controller
- The implementation of most security managers, however, is based entirely upon the access controller.
Permissions
- The basic entity that the access controller operates on is a permission object −− an instance of the Permission class (java.security.Permission). This class, of course, is the basis of the types that are listed in a policy file for the default security policy. The Permission class itself is an abstract class that represents a particular operation. The nomenclature here is a little misleading because a permission object can reflect two things. When it is associated with a class (through a code source and a protection domain), a permission object represents an actual permission that has been granted to that class. Otherwise, a permission object allows us to ask if we have a specific permission.
- For example, if we construct a permission object that represents access to a file, possession of that object does not mean we have permission to access the file. Rather, possession of the object allows us to ask if we have permission to access the file.
The access controller is built upon the four concepts
- Code sources An encapsulation of the location from which certain Java classes were obtained.
- Permissions An encapsulation of a request to perform a particular operation.
- Policies An encapsulation of all the specific permissions that should be granted to specific code sources.
- Protection domains An encapsulation of a particular code source and the permissions granted to that code source.
Byte code verifier
- The verifier is often referred to as a
mini−theorem prover(a term first used in several documents from Sun). This sounds somewhat more impressive than it is; it’s not a generic, all−purpose theorem prover by any means. Instead, it’s a piece of code that can prove one (and only one) thing −− that a given series of ( Java) bytecodes represents a legal set of ( Java) instructions.
Shifting
Java and JavaScript perform sign extension when shift¬ing right, filling the empty spaces with 1’s for negative numbers, so 10100110 » 5 becomes 11111101. The »> operator is unique to Java and JavaScript. It does a logical shift right, filling the empty spaces with 0 no matter what the value, so 10100110 »> 5 becomes 00000101.
The shift operators enable you to multiply and divide by powers of 2 very quickly. For non-negative numbers, shifting to the right one bit is equivalent to dividing by 2, and shifting to the left one bit is equivalent to multiplying by 2. For negative numbers, it obviously depends on the language being used.
Specifically, the bytecode verifier can prove the following:
- The class file has the correct format. The full definition of the class file format may be found in the Java virtual machine specification; the bytecode verifier is responsible for making sure that the class file has the right length, the correct magic numbers in the correct places, and so on.
- Final classes are not subclassed, and final methods are not overridden.
- Every class (except for java.lang.Object) has a single superclass.
- There is no illegal data conversion of primitive data types (e.g., int to Object).
- No illegal data conversion of objects occurs. Because the casting of a superclass to its subclass may be a valid operation (depending on the actual type of the object being cast), the verifier cannot ensure that such casting is not attempted −− it can only ensure that before each such attempt is made, the legality of the cast is tested.
- There are no operand stack overflows or underflows.
Stacks
- In Java, there are two stacks for each thread. One stack holds a series of method frames, where each method frame holds the local variables and other storage for a particular method invocation. This stack is known as the data stack and is what we normally think of as the stack within a traditional program. The bytecode verifier cannot prevent overflow of this stack −− an infinitely recursive method call will cause this stack to overflow. However, each method invocation requires a second stack (which itself is allocated on the data stack) that is referred to as the operand stack; the operand stack holds the values that the Java bytecodes operate on. This secondary stack is the stack that the bytecode verifier can ensure will not overflow or underflow.
Security Manager
- The implementation of the sandbox depends on three things:
- The security manager, which provides the mechanism that the Java API uses to see if security−related operations are allowed.
- The access controller, which provides the basis of the default implementation of the security manager.
- The class loader, which encapsulates information about security policies and classes.
We’ll start by examining the security manager. From the perspective of the Java API, there is a security manager that actually is in control of the security policy of an application. The purpose of the security manager is to determine whether particular operations should be permitted or denied. In truth, the purpose of the access controller is really the same: it decides whether access to a critical system resource should be permitted or denied. Hence, the access controller can do everything the security manager can do.
The reason there is both an access controller and a security manager is mainly historical: the access controller is only available in Java 2 and subsequent releases. Before the access controller existed, the security manager relied on its internal logic to determine the security policy that should be in effect, and changing the security policy required changing the security manager itself. Starting with Java 2, the security manager defers these decisions to the access controller. Since the security policy enforced by the access controller can be specified by using policy files, this allows a much more flexible mechanism for determining policies. The access controller also gives us a much simpler method of granting fine−grained, specific permissions to specific classes. That process was theoretically possibly with the security manager alone, but it was simply too hard to implement.
The BasicPermission class
- If you need to implement your own permission class, the BasicPermission class (java.security.BasicPermission) provides some useful semantics. This class implements a basic permission −− that is, a permission that doesn’t have actions. Basic permissions can be thought of as binary permissions −− you either have them or you don’t. However, this restriction does not prevent you from implementing actions in your subclasses of the BasicPermission class (as the PropertyPermission class does).
-
The prime benefit of this class is the manner in which it implements wildcards. Names in basic permissions are considered to be hierarchical, following a dot−separated convention. For example, if the XYZ corporation wanted to create a set of basic permissions, they might use the convention that the first word of the permission always be xyz: xyz.readDatabase, xyz.writeDatabase, xyz.runPayrollProgram, xyz.HRDepartment.accessCheck, and so on. These permissions can then be specified by their full name, or they can be specified with an asterisk wildcard: xyz.* would match each of these (no matter what depth), and * would match every possible basic permission.
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- 保护密码的最好办法是使用加盐密码哈希（ salted password hashing）。
- 永远不要告诉用户输错的究竟是用户名还是密码。就像通用的提示那样，始终显示：“无效的用户名或密码。”就行了。这样可以防止攻击者在不知道密码的情况下枚举出有效的用户名。
- 应当注意的是，用来保护密码的哈希函数，和数据结构课学到的哈希函数是不同的。例如，实现哈希表的哈希函数设计目的是快速查找，而非安全性。只有加密哈希函数（ cryptographic hash function）才可以用来进行密码哈希加密。像 SHA256 、 SHA512 、 RIPEMD 和 WHIRLPOOL 都是加密哈希函数。
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破解哈希加密最简单的方法是尝试猜测密码，哈希每个猜测的密码，并对比猜测密码的哈希值是否等于被破解的哈希值。如果相等，则猜中。猜测密码攻击的两种最常见的方法是字典攻击和暴力攻击 。
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字典攻击使用包含单词、短语、常用密码和其他可能用做密码的字符串的字典文件。对文件中的每个词都进行哈希加密，将这些哈希值和要破解的密码哈希值比较。如果它们相同，这个词就是密码。字典文件是通过大段文本中提取的单词构成，甚至还包括一些数据库中真实的密码。还可以对字典文件进一步处理以使其更为有效：如单词 “hello” 按网络用语写法转成 “h3110” 。
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暴力攻击是对于给定的密码长度，尝试每一种可能的字符组合。这种方式会消耗大量的计算，也是破解哈希加密效率最低的办法，但最终会找出正确的密码。因此密码应该足够长，以至于遍历所有可能的字符组合，耗费的时间太长令人无法承受，从而放弃破解。
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目前没有办法来组织字典攻击或暴力攻击。只能想办法让它们变得低效。如果密码哈希系统设计是安全的，破解哈希的唯一方法就是进行字典攻击或暴力攻击遍历每一个哈希值了。
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我们可以通过在密码中加入一段随机字符串再进行哈希加密，这个被加的字符串称之为盐值。如上例所示，这使得相同的密码每次都被加密为完全不同的字符串。我们需要盐值来校验密码是否正确。通常和密码哈希值一同存储在帐号数据库中，或者作为哈希字符串的一部分。
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盐值无需加密。由于随机化了哈希值，查表法、反向查表法和彩虹表都会失效。因为攻击者无法事先知道盐值，所以他们就没有办法预先计算查询表或彩虹表。如果每个用户的密码用不同的盐再进行哈希加密，那么反向查表法攻击也将不能奏效。
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一个常见的错误是每次都使用相同的盐值进行哈希加密，这个盐值要么被硬编码到程序里，要么只在第一次使用时随机获得。这样的做法是无效的，因为如果两个用户有相同的密码，他们仍然会有相同的哈希值。攻击者仍然可以使用反向查表法对每个哈希值进行字典攻击。他们只是在哈希密码之前，将固定的盐值应用到每个猜测的密码就可以了。如果盐值被硬编码到一个流行的软件里，那么查询表和彩虹表可以内置该盐值，以使其更容易破解它产生的哈希值。
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用户创建帐号或者更改密码时，都应该用新的随机盐值进行加密。
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出于同样的原因，不应该将用户名用作盐值。对每一个服务来说，用户名是唯一的，但它们是可预测的，并且经常重复应用于其他服务。攻击者可以用常见用户名作为盐值来建立查询表和彩虹表来破解密码哈希。
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为使攻击者无法构造包含所有可能盐值的查询表，盐值必须足够长。一个好的经验是使用和哈希函数输出的字符串等长的盐值。例如， SHA256 的输出为256位（32字节），所以该盐也应该是32个随机字节。
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每个用户的每一个密码都要使用独一无二的盐值。用户每次创建帐号或更改密码时，密码应采用一个新的随机盐值。永远不要重复使用某个盐值。这个盐值也应该足够长，以使有足够多的盐值能用于哈希加密。一个经验规则是，盐值至少要跟哈希函数的输出一样长。该盐应和密码哈希一起存储在用户帐号表中。
- 存储密码的步骤：
- 使用 CSPRNG 生成足够长的随机盐值。
- 将盐值混入密码，并使用标准的密码哈希函数进行加密，如Argon2、 bcrypt 、 scrypt 或 PBKDF2 。
- 将盐值和对应的哈希值一起存入用户数据库。
- 校验密码的步骤：
- 从数据库检索出用户的盐值和对应的哈希值。
- 将盐值混入用户输入的密码，并且使用通用的哈希函数进行加密。
- 比较上一步的结果，是否和数据库存储的哈希值相同。如果它们相同，则表明密码是正确的；否则，该密码错误。
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Whatever is worth doing is worth doing well.
How To Config JFR Java Flight Control
“Climb the mountains and get their good tidings. Nature’s peace will flow into you as sunshine flows into trees. The winds will blow their own freshness i...
How To Read Jdk Mission Control Report
Live the life you’ve imagined.
Jdk Mission Control Can Not Start In Macbook M1
“Climb the mountains and get their good tidings. Nature’s peace will flow into you as sunshine flows into trees. The winds will blow their own freshness i...
How To Keep Multiple Copy Paste Value In Macbook
“Winning is nice if you don’t lose your integrity in the process.” — Arnold Horshak
Google マップ内の写真のコメントが表示されない
紹介 私は、私のOppo Androidスマートフォンのアプリ「Googleマップ」で奇妙な問題が発生していることに気づきました。Googleマップで特定の場所（例えば「中央公園」）を検索すると、通常、このアプリは公園の写真やコメントリストを表示するはずです。例えば、誰かが公園の芝生や川の写真を投稿し、便利な場所...
Les commentaires des photos ne s’affichent pas dans Google Maps.
Introduction J’ai remarqué un problème étrange avec l’application “Google Maps” de mon téléphone Android Oppo. Lorsque vous recherchez un lieu sur Google Map...
Is Kerberos One Ssl/tls?
Nothing is as easy as it looks.
How To Save Expect Script Run Output To File Locally
Nothing is as easy as it looks.
Refind Java Concurrency
You are not a drop in the ocean, you are the entire ocean in a drop.
Refind Java Solid Principles
You are not a drop in the ocean, you are the entire ocean in a drop.
How To Extract Table Name From Sql By Python
You are not a drop in the ocean, you are the entire ocean in a drop.
How to find non-empty json value in mysql
You are not a drop in the ocean, you are the entire ocean in a drop.
master-cglib-in-java
You are not a drop in the ocean, you are the entire ocean in a drop.
What is shape function in python pandas
An honest days’ work makes for a good night’s sleep.
What is shape function in python pandas
Imagination is the key ingredient to a happy life.
What is default logic in python try except else
Keep an eye on the fruits of your labor.
Not just use git but know how git symbolic-ref work
Superheros come in all shapes and sizes.
Fix rejection error in Hexo
The heart can see what is invisible to the eye.
Guide to code productively, get more time back for you
The heart can see what is invisible to the eye.
Is Fibonacci sequence that starts with 0 or 1
The best way to predict the future is to create it.
To increase your productivity 10 times, learn expect and read this blog
Som are born beautiful. The rest of us have to work at it.
Treasure Bowl for SQL, helpful for your daily database jobs
Don’t be greedy. Half of something is better than all nothing.
How to fix most permission issues when using Git
The best way to predict the future is to create it.
One killer page to fix most permission issues when using Git
The best way to predict the future is to create it.
How to check your CPU model and Linux distribution in your AWS VM
Lift is short, enjoy the ride.
2022
Magic-in-Micronaut-JPA
The best way to predict the future is to create it.
谷歌地图里面照片的评论和照片在华为手机里面显示不出来
枝上柳棉吹又少, 天涯何处无芳草. –苏轼
Cannot find symbol class Generated or var
The best way to predict the future is to create it.
GraphQL noteworthy points
Life is like the ocean, it goes up and down.
Scripts bible for MySql
Be the Sun of your solar system.
Minium Workable Mvp Vimrc
”—————————————————————- “ 4. User interface “—————————————————————- “ Set X lines to the cursor when moving vertically set scrolloff=0
How to build unit/integration tests for Spring State Machine
Get busy living or get busy dying.
Magic after maven target spring-boot-run
Turn your wounds into wisdom
Bamboo pipeline deployment failure caused by Kubenetes Finalizer
Today a reader, tomorrow a leader.
Error in WSL in windows, command not found: sdk
Never stop learning, because life never stops teaching.
Could not write JSON: Value out of range. Value: “xxxxx” Radix:10
Life is really simple, but men insist on making it complicated.
Gemfire Geode Error on Peer or client version with ordinal xx not supported. Highest known version is 1.12.1 Client
Take the risk or lose the chance!
Password must not null in gemfire and geode, but I’ve assigned password in yaml properties file
Worries less, smile more!
One page to cover most commonly found errors for fat jar in SpringBoot
Kill time, or kiss time!
Awesome Shortcuts to boost productivity
One must learn by doing the thing; for though you think you know it, you have no certainty, until you try. —Sophocles
Core Java tips required an interview
Success is the sum of small efforts, repeated.
Tell me difference of truststore and keystore in short answer
Do what you say, say what you do.
GIT useful scripts or error solutions
Don’t wish for it, work for it.
Tell me difference of yarn install and npm install in short answer
Don’t find fault. Find a remedy.
Bible blog for most commonly found Gradle errors
People are smarter than you think. Give them a chance to prove themselves.
Pearls in Front end development
Be happy in front of people who don’t like you, it kills them.
Ruby from zero to hero
This is your life. Do what you love, and do it often.
Everything you’d know for Groovy interviews
Life is short. Don’t waste it with negative people who don’t appreciate you. Keep them in your heart but keep them out of your life.
To outstanding as professional MacBook pro user
The most effective way to do it, is to do it Homebrew The best practice is to run brew info before install new software. It will generally list what’s c...
Failed to install gem in Mac, incompatible architecture and missing psych
Burn your ego before it burns you.
IntelliJ Tips to boost your productivity 10 times
Don’t be afraid to make s splash.
Everything you’d know about state machine for interviews
Less expecting, more accepting.
Tips about algorithm resolving from Leetcode
Stay focused, believe that you can achieve at the highest level, surround yourself with others who believe in you and do not stray from your goals.
Solution center for Node errors
Fina a way. If there’s none, make one!
Triple your productivities by Visual studio code keyboard shortcuts
The sentence The quick brown fox jumps over the lazy dog uses every letter of the alphabet.
TypeScript noteworthy notes
The moment you start focusing on yourself, things start falling into place.
RXJS – reactive Programming like a hero
When love is real, it doesn’t lie, cheat, pretend or keep secrets.
Concurrency in Java
Little things make big things happens.
Linux Tips
Remember, some things have to end for better things to begin.
A taste of GraphQL
A good day starts with a good mindset!
A taste of GraphQL
A good day starts with a good mindset!
What’s inside magic in Spring Data JPA
A good day starts with a good mindset!
What’s inside magic in Spring Data JPA
A good day starts with a good mindset!
Why Spring turn a column name from camelNaming to snake_Naming
Don’t spend another year doing the same shit.
Some mistakes you’d avoid in java
With great power comes great responsibilities.
Untold stories for Jupiter, any differences JUnit 5 vs Junit 4
Don’t tell people your plans. Just show them your results!
Git commands you can show off for 100 years
Life is short, make a big splash!
FileNotFound Exception when loading data file in IntelliJ
Take time to do what makes your soul happy!
How to ace AWS certification just like play a game
Life isn’t about finding yourself. Life is about creating yourself.
Java Deep Notes
Java Deep Notes
Code to draw a Big H with all stars
Coding is everything! Code Now!
Code to draw a Big H with all stars
Coding is everything! Code Now!
Single vs Double precisions, float vs double data type
Leave nothing for tomorrow which can be done today. -Abraham Lincoln.
SkipTest-Not-Work-In-Multiple-models-project
Leave nothing for tomorrow which can be done today. -Abraham Lincoln.
SkipTest-Not-Work-In-Multiple-models-project
Leave nothing for tomorrow which can be done today. -Abraham Lincoln.
Maven error and solution on No such host is known
Don’t promis when you are hapy. Don’t reply when you’re angry and don’t decide when you’re sad Service keep on restarting If you spot service is restartin...
Maven error and solution on No such host is known
Don’t promis when you are hapy. Don’t reply when you’re angry and don’t decide when you’re sad
Gradle build stuck
Gradle build stuck, keep on running but never ending
2021
Save my eyes, let your cell phone to read screen content to you
Too much screen time
How logging system Bootstrapped in Spring Boot Application
Summary Following diagram demonstrated the process to bootstrap and use Logback for loggings in Spring Boot applciation.
SQLServer Error about This driver is not configured for integrated authentication
Symptoms When you are using integrated authentication (Kerberos connection) for MS SqlServer connection, there is one possible error :
How to copy files from resources folder in jar and save to a file
Why to extract resources from jar to local disk
Debug of SpringBoot run not working in IntelliJ
Normal approach to debug maven
How to watch specific kubenetes deployment by labels
How to watch specific kubenetes deployment by labels
Failed to talk to github.com from corporation network
Background It’s typical to get various network connection issues when you run commands within corporation network. For example, you’ll find diversed issues w...
Day-Day-Up-Java
More developer friendly Threa Sleep
How to user fire extinguisher
Summary As you know, staff and your safety is paramount. So what if emergency take place, such as fire in office, how to help yourself and your colleagues by...
Deep dive into ApplicationEvent in SpringBoot
Summary As you know, there are various event will be sent (multicast) when a specific story taken place.
2021-09-22-IT-Solutions-For-Remote-Learning
IT-Solutions-For-Remote-Learning.md
Deep dive into Kubernetes Client API
Summary To talk to K8s for getting data, there are few approaches. While K8s’ official Java library is the most widely used one. This blog will look into thi...
How to get CPU name, core, 64bit and speed in command line
Summary In windows operating system, if you want to get your CPU name, core, 64bit and speed in command line. Just follow below actions:
JetBrains/IntelliJ tips
Be a good person in real life, not in social media
Whitelabel Error Page
Summary Whitelabel Error Page is the default error page in Spring Boot web app. It provide a more user-friently error page whenever there are any issues when...
Google maps no photos reviews
Summary
谷歌地图里面照片的评论显示不出来
If you’d like to view solution in YouTube, check out at https://youtu.be/ICiwuqJ-yU8
Shall I still need booster even after I got dose 3?
The greatest wealth is health!
Debts in a nutshell
A debt security represents a debt owed by the issuer to an investor. Here, the investor acts as a lender to the issuer which may be a government, organisatio...
2020
How to process data from S3 download URL
S3 download URL As you know, AWS S3 object can be downloaded/processed by S3 download URL. I’m showing you two examples on how to process S3 Object by NIO f...
Debug Stuck IntelliJ
What happened to a debug job hanging in IntelliJ (IDEAS) IDE? You may find when you try to debug a class in Intellij but it stuck there and never proceed, e....
Awesome Kotlin
Difference with Scala Kotlin takes the best of Java and Scala, the response times are similar as working with Java natively, which is a considerable advantag...
Awesome tips for Chrome
Shortcuts & tips
JVM热身
此文是作者英文原文的翻译文章，英文原文在：http://todzhang.com/posts/2018-06-10-jvm-warm-up/
Awesome tips and shortcuts for Slack
Shortcuts for Slack
Awesome Reactive programming
Key points of Reactive Programming
Awesome Swift for iOS
Frame in Swift
Mock in kotlin
Argument Matching & Answers For example, you have mocked DOC with call(arg: Int): Intfunction. You want to return 1 if argument is greater than 5 and -1 ...
Mock in kotlin
Argument Matching & Answers For example, you have mocked DOC with call(arg: Int): Intfunction. You want to return 1 if argument is greater than 5 and -1 ...
Docker
Dockers Concepts
How to decode path parameters in All REST WebServices calls
How to decode path parameters in All REST WebServices calls
Curl
Linux Curl command
AOP
The concept of join points as matched by pointcut expressions is central to AOP, and Spring uses the AspectJ pointcut expression language by default.
Micrometer notes
As a general rule it should be possible to use the name as a pivot. Dimensions allow a particular named metric to be sliced to drill down and reason about th...
Pigeons in holes principle
# Pigeonhole principle
Awesome solutions for algorithm questions
你就会发现只要涉及递归的问题，都是 树的问题。
A Facial Recognition utility in a dozen of LOC
A Facial Recognition utility in a dozen of python LOC (Lines Of Code)
Awesome SSL certificates and HTTPS
What’s TLS TLS (Transport Layer Security) and its predecessor, SSL (Secure Sockets Layer), are security protocols designed to secure the communication betwee...
JVM warm up by Escape Analysis
Why JVM need warm up I don’t know how and why you get to this blog. But I know the key words in your mind are “warm” for JVM. As the name “warm up” suggested...
Java Concurrent Column 2
This is the second half about Java Concurrent of my blog
Java Concurrent
This blog is about noteworthy pivot points about Java Concurrent Framework Back to Java old days there were wait()/notify() which is error prone, while fr...
Algorithm notes from Leecode – 1
Algorithm Leetcode
2019
Conversations with God
Feelings is the language of the soul. If you want to know what’s true for you about something, look to how your’re feeling about.
Kafka In Spring
Enable Kafka listener annotated endpoints that are created under the covers by a AbstractListenerContainerFactory. To be used on Configuration classes as fol...
Terraform
Why Terraform
Kafka
Kafka
Mifid
FX Spot is not covered by the regulation, as it is not considered to be a financial instrument by ESMA, the European Union (EU) regulator. As FX is considere...
Foreign Exchange
currency pairs Direct ccy: means USD is part of currency pair Cross ccy: means ccy wihtout USD, so except NDF, the deal will be split to legs, both with...
2018
Seconds
nano seconds
Citrix receiver
Simple Binary Encoding (SBE)
Citrix receiver
“Cannot connect to remote desktop” with Citrix Receiver
Guice
A new type of Juice Put simply, Guice alleviates the need for factories and the use of new in your Java code. Think of Guice’s @Inject as the new new. You wi...
YAML
Key points All YAML files (regardless of their association with Ansible or not) can optionally begin with — and end with …. This is part of the YAML format a...
Distruptor
multithreading
Mockito
Feature
Protobuf
What are protocol buffers?
Sudo in a Nutshell
Sudo in a Nutshell Sudo (su “do”) allows a system administrator to give certain users (or groups of users) the ability to run some (or all) commands as root...
Zoo-keeper
ZK Motto the motto “ZooKeeper: Because Coordinating Distributed Systems is a Zoo.”
Presto DB
WHAT IS PRESTO?
Chronicle
Overview
Cucumber
Acceptance testing vs unit test It’s sometimes said that unit tests ensure you build the thing right, whereas acceptance tests ensure you build the right thi...
Scala
Scala String
akka framework of scala
philosophy The actor model adopts the philosophy that everything is an actor. This is similar to the everything is an object philosophy used by some object-o...
File Util in Apache Camel
FileUtil.class
Apache Camel
Camel’s message model In Camel, there are two abstractions for modeling messages, both of which we’ll cover in this section. org.apache.camel.Message—The ...
QuickFixJ
Settings
JXM
Exporting your beans to JMX The core class in Spring’s JMX framework is the MBeanExporter. This class is responsible for taking your Spring beans and registe...
Solace MQ
Solace PubSub+ It is a message broker that lets you establish event-driven interactions between applications and microservices across hybrid cloud environmen...
Apigee
App deployment, configuration management and orchestration - all from one system. Ansible is powerful IT automation that you can learn quickly.
Ansible
Ansible: What Is It Good For? Ansible is often described as a configuration management tool, and is typically mentioned in the same breath as Chef, Puppet, a...
flexbox
How Flexbox works — explained with big, colorful, animated gifs
Jboss tips
commands:
Locking and multithreading
Single Writer principle
KDB
KDB However kdb+ evaluates expressions right-to-left. There are no precedence rules. The reason commonly given for this behaviour is that it is a much simple...
Foreign Exchange
Foreign Exchange markets
Portactor
Better to use smart wait
Agile and SCRUM
Key concept In Scrum, a team is cross functional, meaning everyone is needed to take a feature from idea to implementation.
DevOps-Philosophy
:100:DevOps Model Defined
rxjs pipe in depth
https://stormforger.com/blog/2016/07/08/types-of-performance-testing/
How to setup nodejs to install package from intranet
Error of ‘ECONNRESET’ You may face error ECONNRESET from intranet, even appropriate proxy tools (e.g. cntlm) is running. The errors may looks like ```bash $ ...
Strategy-Of-Openshift-Releases
Release & Testing Strategy There are various methods for safely releasing changes to Production. Each team must select what is appropriate for their own ...
NodeJs Notes
commands to read files var lineReader = require(‘readline’).createInterface({ input: require(‘fs’).createReadStream(‘C:\dev\node\input\git_reset_files.tx...
Minium Viable Product
https://blog.leanstack.com/minimum-viable-product-mvp-7e280b0b9418
What is difference between declarations, providers and import in NgModule
What is difference between declarations, providers and import in NgModule
CORS :Cross-Origin Resource Sharing
Cross-Origin Request Sharing - CORS (A.K.A. Cross-Domain AJAX request) is an issue that most web developers might encounter, according to Same-Origin-Policy,...
ngrx
Why @Effects? In a simple ngrx/store project without ngrx/effects there is really no good place to put your async calls. Suppose a user clicks on a button or...
iOS programming
View A view is also a responder (UIView is a subclass of UIResponder). This means that a view is subject to user interactions, such as taps and swipes. Thus,...
2017
cloud computering
openshift vs openstack The shoft and direct answer is `OpenShift Origin can run on top of OpenStack. They are complementary projects that work well together....
cloud computering
Concepts Cloud computing is the on-demand demand delivery of compute database storage applications and other IT resources through a cloud services platform v...
Redux
whats @Effects You can almost think of your Effects as special kinds of reducer functions that are meant to be a place for you to put your async calls in suc...
reactive programing
The second advantage to a lazy subscription is that the observable doesn’t hold onto data by default. In the previous example, each event generated by the in...
common errors in NPM or node
code E503 code E503 when run npm install packages, e.g.
Container
The Docker project was responsible for popularizing container development in Linux systems. The original project defined a command and service (both named do...
promise vs observiable
The drawback of using Promises is that they’re unable to handle data sources that produce more than one value, like mouse movements or sequences of bytes in ...
Openshift tips
Commands bible
google analysis
How Page Value is calculated
JDK source
interface RandomAccess Marker interface used by List implementations to indicate that they support fast (generally constant time) random access. The primary ...
SSH SFTP
Secure FTP SFTP over FTP is the equivalant of HTTPS over HTTP, the security version
Setup WebSphere profiles and application in command line
Setup WebSphere profiles and application in command line
AWS Tips
After establishing a SSH session, you can install a default web server by executing sudo yum install httpd -y. To start the web server, type sudo service htt...
Oracle
ORA-12899: Value Too Large for Column
Spring notes
Spring Bean Life Cycle Callback Methods
Kindle notes
#《亿级流量网站架构核心技术》目录一览 TCP四层负载均衡 使用Hystrix实现隔离 基于Servlet3实现请求隔离 限流算法 令牌桶算法 漏桶算法 分布式限流 redis+lua实现 Nginx+Lua实现 使用sharding-jdbc分库分表 Disruptor+Redis...
Java JIT compiler
This is talking about Java JIT (Just-In-Time) compiler
Java Security Notes
Java Security well-behaved: programs should be prevent from consuming too much system resources
SeriableVersionUID
Noteworthy points about SeriableVersionUID in Java
R Language
s<-read.csv("C:/Users/xxx/dev/R/IRS/SHH_SCHISHG.csv") # aggregate s2<-table(s$Original.CP) s3<-as.data.frame(s2) # extract by Frequency ordered s3...
SSH and Cryptography
SFTP versus FTPS SS: Secure Shell An increasing number of our customers are looking to move away from standard FTP for transferring data, so we are ofte...
Eclipse notes
How do I remove a plug-in? Run Help > About Eclipse > Installation Details, select the software you no longer want and click Uninstall. (On Macintosh i...
Java JVM
Class loading subsystem
Maven-Notes
Maven philosophy “It is important to note that in the pom.xml file you specify the what and not the how. The pom.xml file can also serve as a documentatio...
Java New IO
Notes JDK 1.0 introduced rudimentary I/O facilities for accessing the file system (to create a directory, remove a file, or perform another task), accessi...
Network Protocols
Net Protocols
IT-Architect
SOA SOA is a set of design principles for building a suite of interoperable, flexible and reusable services based architecture. top-down and bottom-up a...
Algorithm
This page is about key points about Algorithm
Dead Lock
Concept
Java-Tricky-Tech-Questions.md
What is the difference between Serializable and Externalizable in Java? In earlier version of Java, reflection was very slow, and so serializaing large ob...
NavigableMap Misc
What is NavigableMap
Compare-In-Java
Concepts If you implement Comparable interface and override compareTo() method it must be consistent with equals() method i.e. for equal object by equals(...
Java Collections Misc
Difference between equals and deepEquals of Arrays in Java Arrays.equals() method does not compare recursively if an array contains another array on oth...
HashMap in JDK
Hashmap in JDK Some note worth points about hashmap Lookup process Step# 1: Quickly determine the bucket number in which this element may resid...
Java 8 Tips
This blog is listing key new features introduced in Java 8
Arbitrage vs Heading
What is the difference between arbitrage and hedging?
Java Enum Misc
Enum Misc
2016
Java GC notes
verbose:gc verbose:gc prints right after each gc collection and prints details about each generation memory details. Here is blog on how to read verbose gc
Hash Code Misc
contract of hashCode : Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consis...
Apache Tips
Apache
Angulary Misc
Dependency Injection Angular doesn’t automatically know how you want to create instances of your services or the injector to create your service. You must co...
Random number in java
ThreadLocalRandom, SecureRandm, java.util.Random, java.math.Random
Java new features
JDK Versions JDK 1.5 in 2005 JDK 1.6 in 2006 JDK 1.7 in 2011 JDK 1.8 in 2014 Sun之前风光无限，但是在2010年1月27号被Oracle收购。 在被Oracle收购后对外承诺要回到每2年一个realse的节奏。但是20...
用10几行代码自己写个人脸识别程序
用10几行代码自己写个人脸识别程序
Eslastic Search
Eslastic Search
JSON lines
JSON lines
Python Scraphy
Python Scraphy
Simpler chronicle of CI(Continuous Integration) “乱弹系列”之持续集成工具
引言 有句话说有人的地方就有江湖，同样，有江湖的地方就有恩怨。在软件行业历史长河（虽然相对于其他行业来说，软件行业的历史实在太短了，但是确是充满了智慧的碰撞也是十分的精彩）中有一些恩怨情愁，分分合合的小故事，比如类似的有，从一套代码发展出来后面由于合同到期就分道扬镳，然后各自发展成独门产品的Sybase DB和微...
Head First Blockchina 3
Hyperledger Fabric for Mortals
【原创】深入浅出区块链系统：第二章
使用Solidity创建以太坊(Ethereum)智能合约(Smart Contract)
How to customize Sublime syntax highlights
Reference Sublime Scope Naming Syntax Guide
浅谈软件单元测试中的“断言” (assert)，从石器时代进步到黄金时代。
大家都知道，在软件测试特别是在单元测试时,必用的一个功能就是“断言”（Assert)，可能有些人觉得不就一个Assert语句，没啥花头，也有很多人用起来也是懵懵懂懂，认为只要是Assert开头的方法，拿过来就用。一个偶然的机会跟人聊到此功能，觉得还是有必要在此整理一下如何使用以及对“断言”的理解。希望可以帮助大家...
Head First Blockchina 1
深入浅出区块链系统：第一章. what you should know about blockchain
Kubernetes 与 Docker Swarm的对比
Kubernetes 和Docker Swarm 可能是使用最广泛的工具，用于在集群环境中部署容器。但是这两个工具还是有很大的差别。
漫谈开发设计中的一些‘原则’及’设计哲学’
在开发设计中有一些常用原则或者潜规则，根据笔者的经验，这里稍微总结一下最最常用的，以飨读者。
http methods
RFC origion http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.1.2)
Spark-vs-Storm
The stark difference among Spark and Storm. Although both are claimed to process the streaming data in real time. But Spark processes it as micro-batches; wh...
微服务
可以想像一下，之前的传统应用系统，像是一个大办公室里面，有各个部门，销售部，采购部，财务部。办一件事情效率比较高。但是也有一些弊端，首先，各部门都在一个房间里。
unmodifiableList, unmodifiableSet,unmodifiableMap
What’s it Returns an unmodifiable view of the specified set. This method allows modules to provide users with “read-only” access to internal sets. Query ope...
kibana, view layer of elasticsearch
What’s Kibana kibana is an open source data visualization plugin for Elasticsearch. It provides visualization capabilities on top of the content indexed on...
kibana, view layer of elasticsearch
What’s Kibana kibana is an open source data visualization plugin for Elasticsearch. It provides visualization capabilities on top of the content indexed on...
Anatomy of ThreadLocal
Design philosophies
iConnect
UI HTML5, AngularJS, BootStrap, REST API, JSON Backend Hadoop core (HDFS), Hive, HBase, MapReduce, Oozie, Pig, Solr
Business Analysis
Purpose of BA 带来一些商业价值（收益） 解决业务痛点
Something about RESTful architect
REST API must be hypertext driver Roy’s interview
Data Structure
Binary Tree A binary tree is a tree in which no node can have more than two children. A property of a binary tree that is sometimes important is that th...
Useful bookmarks
eBooks list of various books Node.js
heavy load web application
Common solutions
tips in as400 IBM Emulator
Toggle crosshair
Mysql operator to extract JSON
“Be the change you wish to see in the world.” - Mahatma Gandhi
equity trading
Difference between mutal funds and hedge funds
SQL
Differences between not in, not exists , and left join with null
HTTPS/2
concepts
Github page commands notes
404 error for customized domain (such as godday) 404 There is not a GitHub Pages site here. Go to github master branch for gitpages site, manually add CN...
RenMinBi International
RQFII RQFII stands for Renminbi Qualified Foreign Institutional Investor. RQFII was introduced in 2011 to allow qualified foreign institutional investors to ...
JavaScript tips
includes() vs some()
Docker Errors and Fixes
Docker Errors
Load Balancing
Concepts LVS means Linux Virtual Server, which is one Linux built-in component.
Python
(‘—–Unexpected error:’, <type ‘exceptions.TypeError’>) datetime.datetime.now()
Storage Management
RAID RAID is Reductant Array Independent Disk,
CI and CD
Concepts
XA Transactions in 2PC
Description
Setup Git in Mint Linux
How to setup Git in Mint Linux =================================================
Database sharding
DB sharding in YHD
Microservices vs. SOA
Microservice Services are organized around capabilities, e.g., user interface front-end, recommendation, logistics, billing, etc. Services are small in ...
Java Class Loader
Codecache The maximum size of the code cache is set via the -XX:ReservedCodeCacheSize=N flag (where N is the default just mentioned for the particular com...