SecurityContextHolder之策略模式源码分析

springsecurity 之 登录用户数据的获取

springsecurity中，用户登录信息本质是保存到HttpSession中，springsecurity进行封装 获取登录数据有两种思路：

1. 从SecurityContextHolder中获取
2. 从当前请求对象中获取

从SecurityContextHolder中获取

@RestController
public class HelloController {
    @GetMapping("/hello")
    public void hello() {
        Authentication authentication = SecurityContextHolder.getContext().getAuthentication();
        System.out.println("authentication.getClass() = " + authentication.getClass());
    }
}

SecurityContextHolder存放的是SecurityContext ，SecurityContextHolder中定义三种不同的数据存储策略，采用了策略模式

1. MODE_THREADLOCAL ：将SecurityContext放在ThreadLocal中，开启子线程，子线程获取不到用户数据。
2. MODE_INHERITABLETHREADLOCAL：多线程环境，子线程也能获取到用户数据。
3. MODE_GLOBAL：数据保存到一个静态变量中，web开发中很少使用。

SecurityContextHolderStrategy接口用来规范存储策略中的方法

public interface SecurityContextHolderStrategy {
    void clearContext();

    SecurityContext getContext();

    void setContext(SecurityContext var1);

    SecurityContext createEmptyContext();
}

有三个实现类 对应三个不同的存储策略

ThreadLocalSecurityContextHolderStrategy

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//

package org.springframework.security.core.context;

import org.springframework.util.Assert;

final class ThreadLocalSecurityContextHolderStrategy implements SecurityContextHolderStrategy {
    private static final ThreadLocal<SecurityContext> contextHolder = new ThreadLocal();

    ThreadLocalSecurityContextHolderStrategy() {
    }

    public void clearContext() {
        contextHolder.remove();
    }

    public SecurityContext getContext() {
        SecurityContext ctx = (SecurityContext)contextHolder.get();
        if (ctx == null) {
            ctx = this.createEmptyContext();
            contextHolder.set(ctx);
        }

        return ctx;
    }

    public void setContext(SecurityContext context) {
        Assert.notNull(context, "Only non-null SecurityContext instances are permitted");
        contextHolder.set(context);
    }

    public SecurityContext createEmptyContext() {
        return new SecurityContextImpl();
    }
}

存储载体是ThreadLocal 针对SecurityContext的操作都是在ThreadLocal中进行操作。SecurityContext只是个接口，只有一个实现类是SecurityContextImpl

InheritableThreadLocalSecurityContextHolderStrategy

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//

package org.springframework.security.core.context;

import org.springframework.util.Assert;

final class InheritableThreadLocalSecurityContextHolderStrategy implements SecurityContextHolderStrategy {
    private static final ThreadLocal<SecurityContext> contextHolder = new InheritableThreadLocal();

    InheritableThreadLocalSecurityContextHolderStrategy() {
    }

    public void clearContext() {
        contextHolder.remove();
    }

    public SecurityContext getContext() {
        SecurityContext ctx = (SecurityContext)contextHolder.get();
        if (ctx == null) {
            ctx = this.createEmptyContext();
            contextHolder.set(ctx);
        }

        return ctx;
    }

    public void setContext(SecurityContext context) {
        Assert.notNull(context, "Only non-null SecurityContext instances are permitted");
        contextHolder.set(context);
    }

    public SecurityContext createEmptyContext() {
        return new SecurityContextImpl();
    }
}

存储载体为InheritableThreadLocal ，InheritableThreadLocal继承ThreadLocal，多了一个特性，就是在子线程创建的时间，会自动将父线程的数据复制到子线程中。实现了子线程中能够获取登录数据的功能。

GlobalSecurityContextHolderStrategy

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//

package org.springframework.security.core.context;

import org.springframework.util.Assert;

final class GlobalSecurityContextHolderStrategy implements SecurityContextHolderStrategy {
    private static SecurityContext contextHolder;

    GlobalSecurityContextHolderStrategy() {
    }

    public void clearContext() {
        contextHolder = null;
    }

    public SecurityContext getContext() {
        if (contextHolder == null) {
            contextHolder = new SecurityContextImpl();
        }

        return contextHolder;
    }

    public void setContext(SecurityContext context) {
        Assert.notNull(context, "Only non-null SecurityContext instances are permitted");
        contextHolder = context;
    }

    public SecurityContext createEmptyContext() {
        return new SecurityContextImpl();
    }
}

存储载体是一个静态变量，也可以在多线程环境下使用，但用的较少。

SecurityContextHolder源码

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//

package org.springframework.security.core.context;

import java.lang.reflect.Constructor;
import org.springframework.util.ReflectionUtils;
import org.springframework.util.StringUtils;

public class SecurityContextHolder {
    public static final String MODE_THREADLOCAL = "MODE_THREADLOCAL";
    public static final String MODE_INHERITABLETHREADLOCAL = "MODE_INHERITABLETHREADLOCAL";
    public static final String MODE_GLOBAL = "MODE_GLOBAL";
    public static final String SYSTEM_PROPERTY = "spring.security.strategy";
    private static String strategyName = System.getProperty("spring.security.strategy");
    private static SecurityContextHolderStrategy strategy;
    private static int initializeCount = 0;

    public SecurityContextHolder() {
    }

    public static void clearContext() {
        strategy.clearContext();
    }

    public static SecurityContext getContext() {
        return strategy.getContext();
    }

    public static int getInitializeCount() {
        return initializeCount;
    }

    private static void initialize() {
        if (!StringUtils.hasText(strategyName)) {
            strategyName = "MODE_THREADLOCAL";
        }

        if (strategyName.equals("MODE_THREADLOCAL")) {
            strategy = new ThreadLocalSecurityContextHolderStrategy();
        } else if (strategyName.equals("MODE_INHERITABLETHREADLOCAL")) {
            strategy = new InheritableThreadLocalSecurityContextHolderStrategy();
        } else if (strategyName.equals("MODE_GLOBAL")) {
            strategy = new GlobalSecurityContextHolderStrategy();
        } else {
            try {
                Class<?> clazz = Class.forName(strategyName);
                Constructor<?> customStrategy = clazz.getConstructor();
                strategy = (SecurityContextHolderStrategy)customStrategy.newInstance();
            } catch (Exception var2) {
                ReflectionUtils.handleReflectionException(var2);
            }
        }

        ++initializeCount;
    }

    public static void setContext(SecurityContext context) {
        strategy.setContext(context);
    }

    public static void setStrategyName(String strategyName) {
        SecurityContextHolder.strategyName = strategyName;
        initialize();
    }

    public static SecurityContextHolderStrategy getContextHolderStrategy() {
        return strategy;
    }

    public static SecurityContext createEmptyContext() {
        return strategy.createEmptyContext();
    }

    public String toString() {
        return "SecurityContextHolder[strategy='" + strategyName + "'; initializeCount=" + initializeCount + "]";
    }

    static {
        initialize();
    }
}

SecurityContextHolder 定义三个静态常量描述三种不同存储策略，在静态代码块中初始化，根据不同的strategyName初始化不同的存储策略，可以调用配置系统变量或者调用setStrategyName改变策略。

在默认情况下，从子线程中获取登录数据是获取不到的，因为默认是MODE_THREADLOCAL策略。

存储策略在System.getProperty(“spring.security.strategy”);加载，可以配置系统变量来修改策略。

在VM option参数添加

-Dspring.security.strategy=MODE_INHERITABLETHREADLOCAL

SpringContextHolder默认将用户信息存储在ThreadLocal中，在SpringBoot中不同的请求使用不同的线程处理，是怎么获取到用户的信息的呢？ 下篇文章揭晓，有懂的可以在评论区留言。