1，動態(tài)數(shù)據(jù)源類

public class DynamicDataSource extends AbstractRoutingDataSource{

    @Override
    protected Object determineCurrentLookupKey() {
        return DynamicDataSourceHolder.getDbType();//負(fù)載均衡，需要在這里進(jìn)行從庫的key輪詢驱闷。 
    }
}

2耻台，使用本地ThreadLocal，存儲當(dāng)前線程的數(shù)據(jù)源遗嗽。

threadlocal將具體的值保存在線程自身的threadLocalMap中

public abstract class DynamicDataSourceHolder {

    public static final String master = "master";

    public static final String slave = "slave";

    private static final ThreadLocal<String> threadLocal = new ThreadLocal<>();//定義全局ThreadLocal對象粘我，不同線程使用的是同一個對象。

    public static void setDbType(String dbTypeName){
        DynamicDataSourceHolder.threadLocal.set(dbTypeName);
    }

    public static String getDbType(){
        return DynamicDataSourceHolder.threadLocal.get();
    }

    public static void clearDbType(){
        DynamicDataSourceHolder.threadLocal.remove();
    }

}

3痹换，配置多個數(shù)據(jù)源

    @Value("${datasource.username2}")
    private String username2;

    @Value("${datasource.password2}")
    private String password2;

    @Value("${datasource.url2}")
    private String url2;

    @Value("${datasource.username}")
    private String username;

    @Value("${datasource.password}")
    private String password;

    @Value("${datasource.url}")
    private String url;

    @Bean//配置主數(shù)據(jù)庫源
    public DataSource master(){
        DruidDataSource druidDataSource = new DruidDataSource();
        druidDataSource.setUrl(url);
        druidDataSource.setUsername(username);
        druidDataSource.setPassword(password);
        return getDataSource(druidDataSource);
    }
   
   @Bean//配置從數(shù)據(jù)庫源
    public DataSource slave(){
        DruidDataSource druidDataSource = new DruidDataSource();
        druidDataSource.setUrl(url2);
        druidDataSource.setUsername(username2);
        druidDataSource.setPassword(password2);
        return getDataSource(druidDataSource);
    }

    @Bean//配置動態(tài)數(shù)據(jù)源
    public DynamicDataSource dynamicDataSource(){
        DynamicDataSource dynamicDataSource = new DynamicDataSource();
        dynamicDataSource.setDefaultTargetDataSource(master());//default數(shù)據(jù)源
        Map<Object, Object> map = Maps.newHashMap();
        map.put(DynamicDataSourceHolder.master, master());//key - value
        map.put(DynamicDataSourceHolder.slave, slave());
        dynamicDataSource.setTargetDataSources(map);
        return dynamicDataSource;
    }

4征字，自定義注解，標(biāo)識使用哪個數(shù)據(jù)源

@Target({ElementType.METHOD, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Order(Ordered.HIGHEST_PRECEDENCE)
public @interface DynamicSourceAno {

    /**
     * 默認(rèn)使用的數(shù)據(jù)源
     * @return
     */

    String value() default DynamicDataSourceHolder.master;

}

5娇豫，實(shí)現(xiàn)切面匙姜。

設(shè)置spring事務(wù)aop的執(zhí)行順序@EnableTransactionManagement(order = 2) <tx:annotation-driven order="2"/>

@Aspect
@Component
@Order(1)//service層有@Transactional，事務(wù)也是aop實(shí)現(xiàn)的冯痢，這里定義order氮昧，要在事務(wù)開啟的aop執(zhí)行前，進(jìn)行數(shù)據(jù)源的切換浦楣，事務(wù)的aop結(jié)束后袖肥，進(jìn)行數(shù)據(jù)源的恢復(fù)默認(rèn)。
public class DynamicSourceAspect {

    private static Logger logger = LoggerFactory.getLogger(DynamicSourceAspect.class);

    @Before("within(@org.springframework.stereotype.Service *) && @annotation(dynamicSourceAno)")
//在service的所有方法執(zhí)行前振劳，并且?guī)в凶⒔釪ynamicSourceAno
    public void beforeDynamicSource(DynamicSourceAno dynamicSourceAno){

        try {
            DynamicDataSourceHolder.setDbType(dynamicSource.value());
        } catch (Throwable t) {
            logger.info(t.getMessage(), t);
        }

    }

    @After("within(@org.springframework.stereotype.Service *) && @annotation(dynamicSource)")
    public void afterDynamicSource(DynamicSource dynamicSource){

        try {
            DynamicDataSourceHolder.clearDbType();
        } catch (Throwable t) {
            logger.info(t.getMessage(), t);
        }

    }

}

6椎组，ThreadLocal與Thread

1)Thread類。定義了兩個TheadLocalMap類型屬性(可以用來保存對象)历恐，通過ThreadLocal類來維護(hù)的set寸癌，get，remove等操作弱贼。

image.png

2）ThreadLocal類蒸苇。ThreadLocalMap是ThreadLocal的靜態(tài)內(nèi)部類。
Entry類中value屬性用來保存和線程關(guān)聯(lián)的具體對象吮旅，key是ThreadLocal類型

image.png

3）ThreadLocal類操作當(dāng)前線程的ThreadLocalMap溪烤。

//保存value到當(dāng)前線程
public void set(T value) {
        Thread t = Thread.currentThread();//得到當(dāng)前線程
        ThreadLocalMap map = getMap(t);//得到當(dāng)前線程的ThreadLocalMap對象。
        if (map != null)
            map.set(this, value);//將自身對象作為key。每個線程保存這個對象氛什，都是使用相同的key莺葫，因?yàn)樵擃愋偷腡hreadLocal對象只new了一個。
        else
            createMap(t, value);
}

//當(dāng)?shù)谝淮握{(diào)用set方法時枪眉，會創(chuàng)建一個ThreadLocalMap對象。
void createMap(Thread t, T firstValue) {
        t.threadLocals = new ThreadLocalMap(this, firstValue);
}

ThreadLocalMap getMap(Thread t) {
        return t.threadLocals;
}

//從當(dāng)前線程的threadlocals中去除指定key對應(yīng)的value
public T get() {
        Thread t = Thread.currentThread();
        ThreadLocalMap map = getMap(t);
        if (map != null) {
            ThreadLocalMap.Entry e = map.getEntry(this);//不同的線程使用相同的key來取值再层，得到的各自線程保存的對象贸铜。
            if (e != null) {
                @SuppressWarnings("unchecked")
                T result = (T)e.value;
                return result;
            }
        }
        return setInitialValue();
    }