Windows/Linux/Mac下JDK完整安装下载流程

java -version
javac -version
where java

D:\DevTools\Java\jdk-21

%JAVA_HOME%\bin

然后点击"上移"按钮将其移动到靠前的位置，确保系统优先使用此JDK。这样做的目的是避免PATH中其他路径下的java.exe（如某些软件自带的JRE）产生干扰。
如果CLASSPATH变量尚不存在，在"系统变量"区域新建：
| 变量名 | 变量值 |
|--------|--------|
| `CLASSPATH` | `.;%JAVA_HOME%\lib\dt.jar;%JAVA_HOME%\lib\tools.jar` |
> **说明**：上述CLASSPATH中的`dt.jar`和`tools.jar`在Java 9及更高版本中已不存在。对于Java 9+，只需设置`CLASSPATH`为`.;`即可，表示在当前目录中查找类文件。实际上，在现代Java开发中通常不再需要手动设置CLASSPATH环境变量，IDE和构建工具会自动管理类路径。
点击"确定"保存所有设置。
### 3.5 验证安装
打开**新的**命令提示符窗口（注意：必须新开窗口，旧窗口不会继承刚修改的环境变量），依次执行以下命令：
```cmd
java -version

openjdk version "21.0.4" 2024-07-16 LTS
OpenJDK Runtime Environment Temurin-21.0.4+7 (build 21.0.4+7-LTS)
OpenJDK 64-Bit Server VM Temurin-21.0.4+7 (build 21.0.4+7-LTS, mixed mode, sharing)

javac -version

javac 21.0.4

echo %JAVA_HOME%

D:\DevTools\Java\jdk-21

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, Java World!");
        System.out.println("Java Version: " + System.getProperty("java.version"));
        System.out.println("Java Home: " + System.getProperty("java.home"));
    }
}

javac HelloWorld.java
java HelloWorld

Hello, Java World!
Java Version: 21.0.4
Java Home: D:\DevTools\Java\jdk-21

/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"

brew --version
# 输出示例: Homebrew 4.x.x

brew search openjdk

openjdk          openjdk@11       openjdk@17       openjdk@21       openjdk@8
openjdk@24

brew install openjdk@21

# 对于Apple Silicon Mac：
sudo ln -sfn /opt/homebrew/opt/openjdk@21/libexec/openjdk.jdk /Library/Java/JavaVirtualMachines/openjdk-21.jdk
# 对于Intel Mac：
sudo ln -sfn /usr/local/opt/openjdk@21/libexec/openjdk.jdk /Library/Java/JavaVirtualMachines/openjdk-21.jdk

/Library/Java/JavaVirtualMachines/temurin-21.jdk

echo $SHELL
# 输出 /bin/zsh 表示使用 Zsh
# 输出 /bin/bash 表示使用 Bash

# 使用nano编辑器打开配置文件
nano ~/.zshrc
# 或使用vim
vim ~/.zshrc

# ===== Java环境变量配置 =====
export JAVA_HOME=$(/usr/libexec/java_home -v 21)
export PATH=$JAVA_HOME/bin:$PATH
export CLASSPATH=.:$JAVA_HOME/lib

source ~/.zshrc   # 如果使用Zsh
# 或
source ~/.bash_profile   # 如果使用Bash

java -version

openjdk version "21.0.4" 2024-07-16 LTS
OpenJDK Runtime Environment Temurin-21.0.4+7 (build 21.0.4+7-LTS)
OpenJDK 64-Bit Server VM Temurin-21.0.4+7 (build 21.0.4+7-LTS, mixed mode, sharing)

javac -version
# 输出: javac 21.0.4

echo $JAVA_HOME
# 输出: /Library/Java/JavaVirtualMachines/temurin-21.jdk/Contents/Home

/usr/libexec/java_home -V

Matching Java Virtual Machines (2):
    21.0.4 (arm64) "Eclipse Adoptium" - "OpenJDK 21.0.4" /Library/Java/JavaVirtualMachines/temurin-21.jdk/Contents/Home
    17.0.12 (arm64) "Eclipse Adoptium" - "OpenJDK 17.0.12" /Library/Java/JavaVirtualMachines/temurin-17.jdk/Contents/Home

# ===== 多版本JDK切换函数 =====
export JAVA_8_HOME=$(/usr/libexec/java_home -v 1.8)
export JAVA_11_HOME=$(/usr/libexec/java_home -v 11)
export JAVA_17_HOME=$(/usr/libexec/java_home -v 17)
export JAVA_21_HOME=$(/usr/libexec/java_home -v 21)

# 默认使用Java 21
export JAVA_HOME=$JAVA_21_HOME

# 切换函数
alias java8='export JAVA_HOME=$JAVA_8_HOME'
alias java11='export JAVA_HOME=$JAVA_11_HOME'
alias java17='export JAVA_HOME=$JAVA_17_HOME'
alias java21='export JAVA_HOME=$JAVA_21_HOME'

# 查看当前Java版本
alias javaver='java -version'

# 查看系统发行版信息
cat /etc/os-release
# 查看系统架构
uname -m
# x86_64 表示64位x86架构
# aarch64 表示64位ARM架构
# 检查是否已安装Java
java -version 2>/dev/null || echo "未安装Java"
which java

sudo apt update

# 安装Java 21
sudo apt install openjdk-21-jdk -y
# 如需安装Java 17
# sudo apt install openjdk-17-jdk -y
# 如需安装Java 11
# sudo apt install openjdk-11-jdk -y

# 添加Adoptium GPG密钥
wget -qO - https://packages.adoptium.net/artifactory/api/gpg/key/public | sudo apt-key add -
# 添加Adoptium仓库（以Ubuntu 22.04为例）
echo "deb https://packages.adoptium.net/artifactory/deb $(awk -F= '/^UBUNTU_CODENAME/{print$2}' /etc/os-release) main" | sudo tee /etc/apt/sources.list.d/adoptium.list
# 更新并安装
sudo apt update
sudo apt install temurin-21-jdk -y

java -version
javac -version

# 搜索可用的OpenJDK版本
dnf search openjdk
# 安装Java 21
sudo dnf install java-21-openjdk-devel -y
# 安装Java 17
# sudo dnf install java-17-openjdk-devel -y

# 搜索可用的OpenJDK版本
yum search openjdk
# 安装Java 11（CentOS 7默认仓库中最高版本通常为11）
sudo yum install java-11-openjdk-devel -y

# 添加Adoptium RPM仓库
cat <<EOF | sudo tee /etc/yum.repos.d/adoptium.repo
[adoptium]
name=Adoptium
baseurl=https://packages.adoptium.net/artifactory/rpm/\$releasever/\$basearch
enabled=1
gpgcheck=1
gpgkey=https://packages.adoptium.net/artifactory/api/gpg/key/public
EOF
# 安装
sudo dnf install temurin-21-jdk -y

# 进入下载目录
cd /tmp
# 使用wget下载（注意替换为实际的下载链接）
wget https://github.com/adoptium/temurin21-binaries/releases/download/jdk-21.0.4%2B7/OpenJDK21U-jdk_x64_linux_hotspot_21.0.4_7.tar.gz
# 或使用curl下载
# curl -L -o jdk-21.tar.gz https://github.com/adoptium/temurin21-binaries/releases/download/jdk-21.0.4%2B7/OpenJDK21U-jdk_x64_linux_hotspot_21.0.4_7.tar.gz

# 创建安装目录
sudo mkdir -p /usr/lib/jvm
# 解压tar.gz文件
sudo tar -xzf OpenJDK21U-jdk_x64_linux_hotspot_21.0.4_7.tar.gz -C /usr/lib/jvm/
# 查看解压后的目录
ls -la /usr/lib/jvm/

sudo ln -s /usr/lib/jvm/jdk-21.0.4+7 /usr/lib/jvm/jdk-21

nano ~/.bashrc
# 或 vim ~/.bashrc

# ===== Java环境变量配置 =====
export JAVA_HOME=/usr/lib/jvm/jdk-21
export PATH=$JAVA_HOME/bin:$PATH
export CLASSPATH=.:$JAVA_HOME/lib

# 可选：为JRE也设置路径
export JRE_HOME=$JAVA_HOME

source ~/.bashrc

sudo tee /etc/profile.d/java.sh << 'EOF'
# Java环境变量 - 对所有用户生效
export JAVA_HOME=/usr/lib/jvm/jdk-21
export PATH=$JAVA_HOME/bin:$PATH
export CLASSPATH=.:$JAVA_HOME/lib
EOF

# 赋予执行权限
sudo chmod +x /etc/profile.d/java.sh

# 重新登录或执行source使配置生效
source /etc/profile.d/java.sh

java -version
javac -version
echo $JAVA_HOME
which java

# 查看Java可执行文件的实际路径
readlink -f $(which java)
# 查看JDK目录结构
ls -la $JAVA_HOME
# 查看javac的详细信息
javac --help | head -5

# 注册Java 21
sudo update-alternatives --install /usr/bin/java java /usr/lib/jvm/jdk-21/bin/java 2100
sudo update-alternatives --install /usr/bin/javac javac /usr/lib/jvm/jdk-21/bin/javac 2100
# 注册Java 17
sudo update-alternatives --install /usr/bin/java java /usr/lib/jvm/jdk-17/bin/java 1700
sudo update-alternatives --install /usr/bin/javac javac /usr/lib/jvm/jdk-17/bin/javac 1700
# 注册Java 11
sudo update-alternatives --install /usr/bin/java java /usr/lib/jvm/jdk-11/bin/java 1100
sudo update-alternatives --install /usr/bin/javac javac /usr/lib/jvm/jdk-11/bin/javac 1100

sudo update-alternatives --config java

There are 3 choices for the alternative java (providing /usr/bin/java).

  Selection    Path                                   Priority   Status
------------------------------------------------------------
* 0            /usr/lib/jvm/jdk-21/bin/java            2100      auto mode
  1            /usr/lib/jvm/jdk-11/bin/java            1100      manual mode
  2            /usr/lib/jvm/jdk-17/bin/java            1700      manual mode
  3            /usr/lib/jvm/jdk-21/bin/java            2100      manual mode

Press <enter> to keep the current choice[*], or type selection number:

sudo update-alternatives --config javac

update-alternatives --display java

# ===== 多版本JDK管理函数 =====

# 定义各版本路径
export JAVA8_HOME=/usr/lib/jvm/jdk-8
export JAVA11_HOME=/usr/lib/jvm/jdk-11
export JAVA17_HOME=/usr/lib/jvm/jdk-17
export JAVA21_HOME=/usr/lib/jvm/jdk-21

# 默认使用Java 21
export JAVA_HOME=$JAVA21_HOME
export PATH=$JAVA_HOME/bin:$PATH

# 切换函数
java_switch() {
    local version=$1
    case $version in
        8)
            export JAVA_HOME=$JAVA8_HOME
            ;;
        11)
            export JAVA_HOME=$JAVA11_HOME
            ;;
        17)
            export JAVA_HOME=$JAVA17_HOME
            ;;
        21)
            export JAVA_HOME=$JAVA21_HOME
            ;;
        *)
            echo "用法: java_switch {8|11|17|21}"
            return 1
            ;;
    esac
    export PATH=$JAVA_HOME/bin:$(echo $PATH | sed "s|$JAVA_HOME/bin:||g")
    java -version
}

java_switch 17   # 切换到Java 17
java_switch 21   # 切换回Java 21

{
    "java.configuration.runtimes": [
        {
            "name": "JavaSE-21",
            "path": "D:/DevTools/Java/jdk-21",
            "default": true
        }
    ]
}

# Windows
where java

# Linux/macOS
which -a java

# 使用完整路径查看版本
/usr/bin/java -version
/usr/local/bin/java -version

# 创建到标准JVM路径的符号链接
sudo ln -sfn $(brew --prefix)/opt/openjdk@21/libexec/openjdk.jdk /Library/Java/JavaVirtualMachines/openjdk-21.jdk

# Debian/Ubuntu
dpkg -l | grep jdk
# 如果只看到"jre"字样，需要安装开发包
sudo apt install openjdk-21-jdk -y

# RHEL/CentOS
rpm -qa | grep jdk
# 如果只看到"jre"字样，需要安装开发包
sudo dnf install java-21-openjdk-devel -y

# 在.bashrc或.zshrc中添加
export _JAVA_OPTIONS="-Xms256m -Xmx2048m"

# 生成共享归档文件（仅需执行一次）
java -Xshare:dump

# Debian/Ubuntu
sudo apt update && sudo apt upgrade

# RHEL/CentOS/Fedora
sudo dnf update

# macOS (Homebrew)
brew update && brew upgrade

# Windows
# 访问下载页面手动下载新版本安装包