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Go 语言新手笔记（二）

2021-08-13 | 阅读(231)

Go 语方的数组声明方式别具一格，把 [] 看得太重了，看下面的各种声明方式

var a = [...]int{18, 20}            // 这是一个数组，如果省略 ..., 写成  []int{18, 20} 就是一个 slice
var b = [5]string{"hello", 3: "ok"} //指定位置初始化
var c = [...]float32{2.0, 2.3}   // ... 可省略
var d [20]int                 // d 的类型是 [20]int
var e = new([20]int)          // e 的类型是 *[20]int, 这是一个数组指针
var g = [2][2][2]float64      // 多维数组
var h = [...][5]int{{10,20}, {30,40}}   // 类似其他语言一样，只有第一维才能用 [...]

var a = [...]int{18, 20} // 这是一个数组，如果省略 ..., 写成 []int{18, 20} 就是一个 slice

var b = [5]string{"hello", 3: "ok"} //指定位置初始化

var c = [...]float32{2.0, 2.3} // ... 可省略

var d [20]int // d 的类型是 [20]int

var e = new([20]int) // e 的类型是 *[20]int, 这是一个数组指针

var g = [2][2][2]float64 // 多维数组

var h = [...][5]int{{10,20}, {30,40}} // 类似其他语言一样，只有第一维才能用 [...]

再次强调 Go 的数组是值类型，作为函数参数传递会产生副本。避免传入数组产生副本消耗过多内存，办法是可传数组指针或用切片，切片是第一选择。

数组的大小最大为 2GB，用 == 或 != 比较两个数组时它们必须类型和长度一致。阅读全文 >>

Go 语言新手笔记（一）

2021-08-13 | 阅读(344)

Go 语言 2009 年面世，几个成功项目 Docker, Kubernetes, etcs, consul, flannel, 还有 Terraform。Go 编译运行快，听说学习也不难。

安装好 Go 后，有两个环境变量很重要， GOPATH 是工作目录，GOROOT 是 Go 的安装目录, 如 /usr/local/go。GOPATH 允许多个目录，用 : 或 ;(Windows 下) 分隔，当 GOPATH 有多个目录，go get 命令的包放在第一个目录下。

src: 存放 .go, .c, .h, .s 等源码文件，go run, go install 等命令也要在该目录下执行
pkg: 存放编译时生成的中间文件，如 .a
bin: 存放编译后的可执行文件

Go 编程是声明了不用的全局变量是绝对的罪过，编译这一关过不了。Go 用 var 声明变量，如 var b bool = true。Go 有精确长度的丰富的基本类型，如 int8, int16, int32, int64, unit8, float32(6位精度), float64(15位精度) 等，单纯写成 int, unit 时，长度与系统有关。Go 的字符串用 UTF-8 格式编码的 Unicode 字符，每个字符对应一个 rune 类型，rune 是字符的意思，相当于 int32. 阅读全文 >>

pm2 使用笔记

2021-08-12 | 阅读(1,814)

PM 2 是什么，官网上 https://pm2.keymetrics.io/ 是说 PM2(Process Manager 2) 是 Node JS 的高级的，产品级的进程管理工具。为什么叫做 PM2，那有没有 PM 或 PM 1 呢，没有，它起步就是 2. PM2 相对于 Node JS 有点类似于 Gunicorn 和 Python Web 应用的关系。但 PM2 比 Gunicorn 功能更强大, 其实 PM2 还能用来管理其他任何进程，不局限于 Node JS 的。

最好的入门学习教程是官方的 Quick Start。从中我们可以大概看到 PM2 的主要应用：

对进程的管理与监控
多种进程重启策略
日志的管理
使用配置文件
集群模式
用作静态 Web 服务
进行应用部署
使用环境变量

PM2 是 Node JS 应用，所以它是跨平台的。阅读全文 >>

Docker Compose In Practice

2021-06-24 | 阅读(537)

Continue to advance to Kubernetes, the last article Docker Swarm In Action, After understanding Swarm, it is necessary to get familiar with Docker Compose. Docker Swarm forms a cluster of Docker hosts. As long as the Manager node is notified when the service is deployed, it will automatically find the corresponding node to run containers. Compose is another concept entirely. It organizes multiple associated containers into a whole for deployment, such as a load balance container, multiple web containers, and a Redis cache container to make up a whole bundle.

Revealed by its name, Compose, the concept of container orchestration was officially established. Later, Kubernetes, which we will learn, it's a tool for higher-level organization, operation and management of containers. Because Compose organizes the containers, it can start multiple associated containers with one command, instead of starting one container separately.

Regarding the installation of Docker Compose, Docker Desktop under Mac OS X comes with docker-compose; since Docker Compose is written in Python, we can use pip install docker-compose to install it, and use its commands after installation docker-compose. 阅读全文 >>

Docker Swarm In Action

2021-06-24 | 阅读(768)

Before officially entering into Kubernetes, I hope to know something about the earlier Docker Swarm, although it is basically no long used currently. Swarm provides a cluster of Docker hosts. There is at least one Manager (or more) in the cluster, plus 0 or more Workers. The main idea is that a Docker service (container) is executed by the Swarm cluster manager, and it will find the corresponding host in the cluster to execute the container. Both Manager and Worker can to run Docker containers, but only Manager can execute management commands.

The following two pictures shows the difference between running Docker containers on a host and a Swarm cluster host.

Run all containers in one host

Run container together

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Introduce Vagrant and common usages

2021-06-24 | 阅读(568)

Many of my demos about Kafka, Docker, Python, Kubernates, and etc. are made with Vagrant virtual machines. It is time to write a blog for some frequently used Vagrant commands. Vagrant is a member of the HashiCorp family. Others of HashiCorp's famous tools include Terraform , Consul , Vault , Boundary , Packer , Nomad and Waypoint .

Speaking of Vagrant, I have to mention the similar Docker, in fact, they are quite different, while they both give people the external feeling that they are command line control Linux. Vagrant is essentially a virtual machine shell, allowing us to use Vagrant commands to interact with the virtual machine more conveniently, instead of switching back and forth between the host machine and the virtual machine, it is more convenient to manage multiple virtual machines in one single terminal; while Docker is a container, The essence of a container is a process on the host machine, but it is isolated from the file system, process, network, etc. of the process with a namespace, making the container process look like a virtual OS.

Vagrant is a tool for the development environment, and Docker is a tool for the deployment environment; Vagrant operates a standard Linux or Windows operating system, and the Docker is very critical on image size. Docker image is usually a trimmed system, just has necessary command to run our service. Since Vagrant corresponds to a virtual machine, the operation status with Vagrant and the installed software will be retained after Vagrant virtual machine shutdown, while the operations status in Docker are all for the current container (copy-on-write), which does not affect the corresponding image , Unless it is committed as a new image with docker commit.

Understand that Vagrant is just the shell of a virtual machine, so it requires different virtual machine implementations, such as VirtualBox, Hyper-V, VMware, etc., and we can use Vagrant to interact with Docker as well. Vagrant can support multiple Operation Systems. 阅读全文 >>

为 Java 注册 classpath: 协议用 URL 读取文件

2021-06-17 | 阅读(1,066)

本文为 Java 注册 classpath 协议读取文件的目的就是要让下面的代码能工作起来

String text = IOUtils.toString(new URL("classpath:/db.properties"), "UTF-8");
System.out.println(text);

1 2	String text = IOUtils.toString(new URL("classpath:/db.properties"), "UTF-8"); System.out.println(text);

假设在 classpath 下有个文件 db.properties, 比如在 Maven 项目的 src/main/resources 目录中，或是在某个 jar 包的根位置。如果我们直接执行上面的代码将会得到异常

Exception in thread "main" java.net.MalformedURLException: unknown protocol: classpath
at java.net.URL.<init>(URL.java:617)
at java.net.URL.<init>(URL.java:507)

说是不认识的 classpath 协议。

前面代码是有实际用途的，比如说我们使用 XML 时就能支持远程协议

Document document = DocumentBuilderFactory.newInstance().newDocumentBuilder()
    .parse("https://www.w3schools.com/xml/note.xml");
System.out.println(document.getDocumentElement().getTagName());

Document document = DocumentBuilderFactory.newInstance().newDocumentBuilder()

.parse("https://www.w3schools.com/xml/note.xml");

System.out.println(document.getDocumentElement().getTagName());

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Java 10 ~ 16 一路向前冲(新特性一箩筐)

2021-05-08 | 阅读(758)

Java 一路突突突，版本 16 在 2021-03-16 都发布了, 而我们一直碍于 Java 9 的大改还在 Java 8 上原地踏步, 以往每当有新版本 JDK 发布后都是很快就验证，立马升级。Java SE versions history) 列出了所有 Java 的历史版本的发布日期。在今天(2021-05-04) 网站 Java SE Downloads 上直接提供下载的 Java SE 版本有以下三

Java SE 16.0.1
Java SE 11.0.11(LTS)
Java SE 8u291

两个 LTS(长期支持) 版 8 和 11，外加一个目前最新的非 LTS 版本 16, 其他的版本都被归档到了 Java Archive. 查看一下 Java 支持的 roadmap, 几个 LTS 版本的服务支持年限

版本本发布日原定支持至延期支持至
Java 8 2014/3 2022/3 2030/12
Java 11 2018/9 2023/9 2026/9
Java 17 2021/9 2026/9 2029/9

注意到 Java 8 将比 Java 11 和将来的 Java 17 生命力还顽强，一下就觉得这么久坚守在 Java 8 的阵地上不应觉得有什么好害羞的。眼看着下一个 LTS 版本的 Java 17 就要在今年 9 月份发布了，Java 11 看来是要错过了，等准备好和 Java 8 告别时要直接跳到 Java 17 了。阅读全文 >>

探索 Apache, Tomcat, SpringBoot 对请求数据的解压缩

2021-05-04 | 阅读(953)

通常我们都会配置 Web 服务端对响应数据进行压缩，如用 Apache 的 mod_deflate 模块，或配置 Tomcat connector 启用压缩，又或者是在 Java Web 项目中加 Web Filter 来压缩特定的响应数据。这样客户端发送 HTTP 请求时在头中声明如 Accept-Encoding: gzip，服务端就可能会对响应数据进行压缩，同时带上 Content-Encoding: gzip 响应头。

有时候 HTTP Post 的数据太大同样会要求客户端在传输数据之前对请求数据进行压缩，本文主要关注服务端如何自动解压客户端发出的压缩数据。

先以 Apache2 为例，以 Ubuntu 20.04 为例，用命令 apt-get install apache2 安装 Apache 2.4.41, 它自动启用了 mod_deflate 模块。mod_deflate 模块的配置文件 /etc/apache2/modes-enabled/deflate.conf 内容如下

<IfModule mod_deflate.c>
    <IfModule mod_filter.c>
        AddOutputFilterByType DEFLATE text/html text/plain text/xml text/css
        AddOutputFilterByType DEFLATE application/x-javascript application/javascript application/ecmascript
        AddOutputFilterByType DEFLATE application/rss+xml
        AddOutputFilterByType DEFLATE application/xml
    </IfModule>
</IfModule>

AddOutputFilterByType DEFLATE text/html text/plain text/xml text/css

AddOutputFilterByType DEFLATE application/x-javascript application/javascript application/ecmascript

AddOutputFilterByType DEFLATE application/rss+xml

AddOutputFilterByType DEFLATE application/xml

</IfModule>

它表示只对以上特定的响应数据类型进行压缩，下面来测试下对 html 内容的压缩阅读全文 >>

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