2020-10_ Development experience set

1. java 1.7 New specification , You can underline the value , To enhance readability .

• You cannot underline values before and after
• You cannot underline around the decimal point
• You cannot underline multiple consecutive non numeric numbers

2. What is? CAS Mechanism ？

CAS(Compare and Swap) Compare and replace ,CAS The mechanism uses 3 Basic operands ： Memory address V, Old expectations A, New value to modify B.
When updating a variable , Only when the expected value of the variable A And memory address V When the actual values are the same , The memory address V The corresponding value is modified to B.
CAS The shortcomings of ：

• CPU Spending too much
  In the case of high concurrency , If many threads repeatedly try to update a variable , But it has not been updated successfully , cycle , Will give CPU Bring a lot of pressure .
• There's no guarantee that the code block is atomic
  CAS What the mechanism guarantees is only the atomic operation of a variable , It doesn't guarantee the atomicity of the whole code block . For example, guarantee is needed 3 All variables are updated atomically , You have to use it synchronized 了 .
• ABA problem

3. Maven How to configure HTTP agent

In enterprise development , Many companies will use Intranet in consideration of network security , Some small partners who have just arrived at the company will find after installing the environment , Because you can't connect to the Internet Maven Can't get down from the library , This is the time when Maven Intermediate configuration agent .
The specific operation steps are as follows ：
1. Open the download Maven File in conf Folder , find settings.xml file
2. open settings.xml file , find label , Paste the following code

<proxy>
        <!--id  The name of the agent （ Set casually ）-->
        <id>optional</id>
        <!--true  It means effective -->
        <active>true</active>
        <!-- agreement -->
        <protocol>http</protocol>
        <!-- Internet user name and password of this machine , without , Please comment or delete -->
        <username>*******.ex</username>
        <password>a*169646</password>
        <!-- The company uses the Internet ip And port , I.e. agency , Replace here with the corresponding ip And port -->
        <host>127.0.0.1</host>
        <port>11171</port>
        <!-- Fill in the address without agency , With vertical lines | Split multiple addresses , Usually fill in local Maven Warehouse address -->
        <nonProxyHosts>local.net|some.host.com</nonProxyHosts>
    </proxy>

4. annotation @JsonUnwrapped Flatten the object

Reference article ：https://blog.csdn.net/tangyaya8/article/details/101513670

5. Spring in propagation Of 7 Transaction configurations

In declarative transactions , To configure a section , It uses propagation, Indicates how you intend to use transactions for these methods , Use it or not , among propagation There are seven configurations ,REQUIRED、SUPPORTS、MANDATORY、REQUIRES_NEW、NOT_SUPPORTED、NEVER、NESTED. The default is REQUIRED.

• REQUIRED： Support current transaction , If there is no current transaction , Just create a new transaction . This is the most common choice .
• SUPPORTS： Support current transaction , If there is no current transaction , Just in a non transactional way .

6. spring Of RestTemplate Use guide

Reference article ：https://www.cnblogs.com/wyq178/p/9058030.html

7. Plug ins and tools

• Browser background plugin ：DarkReader
• Vertica database (TODO)
• Kafka middleware (TODO)
• Kubectl Use summary (TODO)

8. word

• stain Stain
• acne acne
• mask masks
• scar Scars
• dimple Dimple
• wrinkle Wrinkle
• pouch Bag
• retrieval data retrieval