ThreadLocal学习笔记

    /**
     * Sets the current thread's copy of this thread-local variable
     * to the specified value.  Most subclasses will have no need to
     * override this method, relying solely on the {@link #initialValue}
     * method to set the values of thread-locals.
     *
     * @param value the value to be stored in the current thread's copy of
     *        this thread-local.
     */
    public void set(T value) {
        Thread t = Thread.currentThread();
        ThreadLocalMap map = getMap(t);
        if (map != null)
            map.set(this, value);
        else
            createMap(t, value);
    }

    /**
     * Get the map associated with a ThreadLocal. Overridden in
     * InheritableThreadLocal.
     *
     * @param  t the current thread
     * @return the map
     */
    ThreadLocalMap getMap(Thread t) {
        return t.threadLocals;
    }

    /**
     * Create the map associated with a ThreadLocal. Overridden in
     * InheritableThreadLocal.
     *
     * @param t the current thread
     * @param firstValue value for the initial entry of the map
     */
    void createMap(Thread t, T firstValue) {
        t.threadLocals = new ThreadLocalMap(this, firstValue);
    }

    /**
     * Returns the value in the current thread's copy of this
     * thread-local variable.  If the variable has no value for the
     * current thread, it is first initialized to the value returned
     * by an invocation of the {@link #initialValue} method.
     *
     * @return the current thread's value of this thread-local
     */
    public T get() {
        Thread t = Thread.currentThread();
        ThreadLocalMap map = getMap(t);
        if (map != null) {
            ThreadLocalMap.Entry e = map.getEntry(this);
            if (e != null) {
                @SuppressWarnings("unchecked")
                T result = (T)e.value;
                return result;
            }
        }
        return setInitialValue();
    }

 /**
     * Variant of set() to establish initialValue. Used instead
     * of set() in case user has overridden the set() method.
     *
     * @return the initial value
     */
    private T setInitialValue() {
        T value = initialValue();
        Thread t = Thread.currentThread();
        ThreadLocalMap map = getMap(t);
        if (map != null)
            map.set(this, value);
        else
            createMap(t, value);
        return value;
    }

   /**
     * Returns the current thread's "initial value" for this
     * thread-local variable.  This method will be invoked the first
     * time a thread accesses the variable with the {@link #get}
     * method, unless the thread previously invoked the {@link #set}
     * method, in which case the {@code initialValue} method will not
     * be invoked for the thread.  Normally, this method is invoked at
     * most once per thread, but it may be invoked again in case of
     * subsequent invocations of {@link #remove} followed by {@link #get}.
     *
     * <p>This implementation simply returns {@code null}; if the
     * programmer desires thread-local variables to have an initial
     * value other than {@code null}, {@code ThreadLocal} must be
     * subclassed, and this method overridden.  Typically, an
     * anonymous inner class will be used.
     *
     * @return the initial value for this thread-local
     */
    protected T initialValue() {
        return null;
    }

    private static ThreadLocal<Integer> threadLocal = new ThreadLocal<Integer>() {
        protected Integer initialValue() {
            return 0;
        }
    };

private static ThreadLocal<Connection> connectionHolder = new ThreadLocal<Connection>() {
    public Connection initialValue() {
        return DriverManager.getConnection(DB_URL);
    }
};
 
public static Connection getConnection() {
    return connectionHolder.get();
}

public class RequestThreadLocal {
    private static final ThreadLocal<HttpServletRequest> threadLocal = new ThreadLocal<HttpServletRequest>();
    private static final ThreadLocal<List<String>> historyThreadLocal = new ThreadLocal<List<String>>();
    private static final Log log = LogFactory.getLog(RequestThreadLocal.class);
    
    public static HttpServletRequest get(){
        return threadLocal.get();
    }
    
    public static void set(HttpServletRequest request){
        log.debug("Put the pagination object into thread local");
        threadLocal.set(request);
    }
    public static void remove(){
        log.debug("clear the pagination object from thread local which related with current thread.");
        threadLocal.set(null);
    }
}

//调用
@Controller
public class ControllerFilter implements Filter{
    @Override
    public void destroy() {}

    @Override
    public void doFilter(ServletRequest req, ServletResponse res,
            FilterChain chain) throws IOException, ServletException {
            RequestThreadLocal.set((HttpServletRequest) req);
            chain.doFilter(req, res);
            RequestThreadLocal.remove();
    }

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {}
}

//调用
/**
 * 获取当前登录用户
 * @return
 */
public static AclUserDto getLoginUser(){
     HttpSession session = RequestThreadLocal.get().getSession();
     return (AclUserDto) session.getAttribute(LoginInfo.SESSIONUSER.getDesc());
}

@Component
@Aspect
public class DataSourceMethodInterceptor {

    @Before("execution(* com.xxx.xxx.xxx.xxx.service.impl.*.*(..))")
    public void dynamicSetDataSoruce(JoinPoint joinPoint) throws Exception {
        String methodName = joinPoint.getSignature().getName();
        // 查询读从库
        if (methodName.startsWith("select") || methodName.startsWith("load") || methodName.startsWith("get") || methodName.startsWith("count") || methodName.startsWith("is")) {
            DynamicDataSourceHolder.setDataSource("slave");
        } else { // 其他读主库
            DynamicDataSourceHolder.setDataSource("master");
        }
    }

}