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Spring 注解编程 Bean 配置

@Configuration

@Configuration 配置类

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import org.springframework.context.annotation.*;

@Configuration
public class MainConfig {

}

测试类

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import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class MainConfigTest {

    public static void main(String[] args) {
        AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();

		// 注册 MainConfig
        ctx.register(MainConfig.class);
        // 刷新容器
        ctx.refresh();

        // 获取容器中定义的所有 bean
        String[] beanDefinitionNames = ctx.getBeanDefinitionNames();
        for (String beanDefinitionName : beanDefinitionNames) {
            System.out.println(beanDefinitionName);
        }
        ctx.close();
    }
}

@Bean

xml 配置

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<bean id="user" class="com.github.User"></bean>

java config

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@Bean
public User user() {
	return new User();
}

@Import

@Import 导入bean

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@Configuration
public class UserConfig {

	@Bean
	public User user() {
		return new User();
	}
}


@Configuration
@Import({UserConfig.class}) // 使用 import 导入 UserConfig
public class MainConfig {

}

public static void main(String[] args) {
    ApplicationContext ctx = new AnnotationConfigApplicationContext(MainConfig.class);
    User user = ctx.getBean(User.class);
    System.out.println(user);
}

org.springframework.context.annotation.ImportSelector 选择导入

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public class UserImportSelector implements ImportSelector {

	@Override
    public String[] selectImports(AnnotationMetadata annotationMetadata) {
    	return new String[] {"com.github.User"};
    }
}

@Configuration
@Import({UserImportSelector.class})
public class MainConfig {

}

public static void main(String[] args) {
    ApplicationContext ctx = new AnnotationConfigApplicationContext(MainConfig.class);
    User user = ctx.getBean(User.class);
    System.out.println(user);
}

org.springframework.context.annotation.ImportBeanDefinitionRegistrar 注册Bean

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class UserRegistrar implements ImportBeanDefinitionRegistrar {

	@Override
	public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
		RootBeanDefinition beanDefinition = new RootBeanDefinition(User.class);
		registry.registerBeanDefinition("user", beanDefinition);
	}

}

@Configuration
@Import({UserRegistrar.class})
public class MainConfig {

}

public static void main(String[] args) {
    ApplicationContext ctx = new AnnotationConfigApplicationContext(MainConfig.class);
    User user = ctx.getBean(User.class);
    System.out.println(user);
}

spring 注解编程中 @Enable** 组件，大量使用此种方式注册Bean。例：@EnableAspectJAutoProxy

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@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(AspectJAutoProxyRegistrar.class) // 此处导入
public @interface EnableAspectJAutoProxy {

	/**
	 * Indicate whether subclass-based (CGLIB) proxies are to be created as opposed
	 * to standard Java interface-based proxies. The default is {@code false}.
	 */
	boolean proxyTargetClass() default false;

	/**
	 * Indicate that the proxy should be exposed by the AOP framework as a {@code ThreadLocal}
	 * for retrieval via the {@link org.springframework.aop.framework.AopContext} class.
	 * Off by default, i.e. no guarantees that {@code AopContext} access will work.
	 * @since 4.3.1
	 */
	boolean exposeProxy() default false;

}

@ComponentScan

@ComponentScan 指定扫描的包目录

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package com.github;

@Component
public class User {

}
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@Configuration
@ComponentScan({"com.github"})
public class MainConfig {

}

@Profile

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@Configuration
public class MainConfig {


    @Profile("dev")
    @Bean
    public User devUser() {
        return new User();
    }
}


public class MainConfigTest {

    public static void main(String[] args) {
        AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();

        ConfigurableEnvironment env = ctx.getEnvironment();
        env.setActiveProfiles("dev"); // 设置环境为 dev

        ctx.register(MainConfig.class);
        ctx.refresh();

        User user = ctx.getBean(User.class);
        System.out.println(user);

        ctx.close();
    }
}

在实际开发中，经常有开发，测试，生产环境的不同配置，使用 @Profile 可以有效解决。 命令行启动设置激活的 Profile java -Dspring.profiles.actives=dev app.jar 。

initMethod destroyMethod Bean 生命周期

基于 @Bean 配置

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public class User {

    public void initMethod() {
        System.out.println("user initMethod");
    }

    public void destroyMethod() {
        System.out.println("user destroyMethod");
    }
}
@Configuration
public class MainConfig {


    @Bean(initMethod="initMethod", destroyMethod="destroyMethod")
    public User devUser() {
        return new User();
    }
}

继承 org.springframework.beans.factory.InitializingBean 和 org.springframework.beans.factory.DisposableBean

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public class User implements InitializingBean, DisposableBean {

    public void afterPropertiesSet() throws Exception {
        System.out.println("user initMethod");
    }

    public destroy() throws Exception {
        System.out.println("user destroyMethod");
    }
}
@Configuration
public class MainConfig {


    @Bean
    public User devUser() {
        return new User();
    }
}

使用 javax.annotation.PostConstruct 和 javax.annotation.PreDestroy。 注意这两个注解是Java规范并不是spring内置的，

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public class User {

    @PostConstruct
    public void initMethod() {
        System.out.println("user initMethod");
    }

    @PreDestroy
    public void destroyMethod() {
        System.out.println("user destroyMethod");
    }
}
@Configuration
public class MainConfig {


    @Bean
    public User devUser() {
        return new User();
    }
}

@Scope

scope 取值:通常使用 singleton, prototype。 web环境有 request, session。 batch 环境 step。

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@Bean(initMethod="initMethod", destroyMethod="destroyMethod")
@Scope("prototype")
public User devUser() {
    return new User();
}

默认是singleton的，这里比较一下prototype有什么不同:

  • 每次在容器中获取的 User 都会调用 devUser() 方法获取 User 实例。
  • 关闭容器不会调用 destroyMethod() 方法。

org.springframework.beans.factory.config.BeanPostProcessor Bean 实例化前置处理器

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public interface BeanPostProcessor {

	/**
	 * Apply this BeanPostProcessor to the given new bean instance <i>before</i> any bean
	 * initialization callbacks (like InitializingBean's {@code afterPropertiesSet}
	 * or a custom init-method). The bean will already be populated with property values.
	 * The returned bean instance may be a wrapper around the original.
	 * @param bean the new bean instance
	 * @param beanName the name of the bean
	 * @return the bean instance to use, either the original or a wrapped one;
	 * if {@code null}, no subsequent BeanPostProcessors will be invoked
	 * @throws org.springframework.beans.BeansException in case of errors
	 * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
	 */
	Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException;

	/**
	 * Apply this BeanPostProcessor to the given new bean instance <i>after</i> any bean
	 * initialization callbacks (like InitializingBean's {@code afterPropertiesSet}
	 * or a custom init-method). The bean will already be populated with property values.
	 * The returned bean instance may be a wrapper around the original.
	 * <p>In case of a FactoryBean, this callback will be invoked for both the FactoryBean
	 * instance and the objects created by the FactoryBean (as of Spring 2.0). The
	 * post-processor can decide whether to apply to either the FactoryBean or created
	 * objects or both through corresponding {@code bean instanceof FactoryBean} checks.
	 * <p>This callback will also be invoked after a short-circuiting triggered by a
	 * {@link InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation} method,
	 * in contrast to all other BeanPostProcessor callbacks.
	 * @param bean the new bean instance
	 * @param beanName the name of the bean
	 * @return the bean instance to use, either the original or a wrapped one;
	 * if {@code null}, no subsequent BeanPostProcessors will be invoked
	 * @throws org.springframework.beans.BeansException in case of errors
	 * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
	 * @see org.springframework.beans.factory.FactoryBean
	 */
	Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException;

}

实现此接口会在spring容器初始化bean时调用

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HashMap 的使用

在开发中经常使用到 HashMap，分析一下 HashMap 带参的构造方法

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/**
  * Constructs an empty <tt>HashMap</tt> with the specified initial
  * capacity and load factor.
  *
  * @param  initialCapacity the initial capacity
  * @param  loadFactor      the load factor
  * @throws IllegalArgumentException if the initial capacity is negative
  *         or the load factor is nonpositive
  */
public HashMap(int initialCapacity, float loadFactor) {
    if (initialCapacity < 0)
        throw new IllegalArgumentException("Illegal initial capacity: " +
                                            initialCapacity);
    if (initialCapacity > MAXIMUM_CAPACITY)
        initialCapacity = MAXIMUM_CAPACITY;
    if (loadFactor <= 0 || Float.isNaN(loadFactor))
        throw new IllegalArgumentException("Illegal load factor: " +
                                            loadFactor);
    this.loadFactor = loadFactor;
    this.threshold = tableSizeFor(initialCapacity);
}

/**
  * Constructs an empty <tt>HashMap</tt> with the specified initial
  * capacity and the default load factor (0.75).
  *
  * @param  initialCapacity the initial capacity.
  * @throws IllegalArgumentException if the initial capacity is negative.
  */
public HashMap(int initialCapacity) {
    this(initialCapacity, DEFAULT_LOAD_FACTOR);
}

/**
  * Constructs an empty <tt>HashMap</tt> with the default initial capacity
  * (16) and the default load factor (0.75).
  */
public HashMap() {
    this.loadFactor = DEFAULT_LOAD_FACTOR; // all other fields defaulted
}

一个参数的构造方法，传入的参数是初始大小，最终调用两个参数的构造方法，传入初始大小和负载系数。默认的负载系数 DEFAULT_LOAD_FACTOR 是 0.75f.调用tableSizeFor(int)传入初始大小值算出threshold，具体的 tableSizeFor(int) 方法,threshold实际值会在第一次put(k,v)重新计算。

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/**
  * Returns a power of two size for the given target capacity.
  */
static final int tableSizeFor(int cap) {
    int n = cap - 1;
    n |= n >>> 1;
    n |= n >>> 2;
    n |= n >>> 4;
    n |= n >>> 8;
    n |= n >>> 16;
    return (n < 0) ? 1 : (n >= MAXIMUM_CAPACITY) ? MAXIMUM_CAPACITY : n + 1;
}

写一个测试 tableSizeFor 方法算出的结果

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public static void main(String[] args) {
  for(int i = 0; i < 20; i++) {
    System.out.println(i+":"+tableSizeFor(i));
  }
}
static final int MAXIMUM_CAPACITY = 1 << 30;

static final int tableSizeFor(int cap) {
  int n = cap - 1;
  n |= n >>> 1;
  n |= n >>> 2;
  n |= n >>> 4;
  n |= n >>> 8;
  n |= n >>> 16;
  return (n < 0) ? 1 : (n >= MAXIMUM_CAPACITY) ? MAXIMUM_CAPACITY : n + 1;
}

分析输出，这里输出的规律是，最小的2的幂

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0:1
1:1
2:2
3:4
4:4
5:8
6:8
7:8
8:8
9:16
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19:32

put(k,v)如果是第一次调用会直接调用resize()计算threshold分配table大小，方法在最后会判断size大小是否大于 threshold,如果插入元素大于threshold则调用resize(),然后重新计算 threshold，调整table的大小.阅读源码发现threshold计算方式是table大小乘负载系数 DEFAULT_LOAD_FACTOR.也就是说如果new HashMap(8)，在第一次put(k,v)时会计算出threshold为6(负载系数0.75)，在第6个参数put(k,v)时，就会重新扩容。扩容的算法使用左移<<算出结果等同*2。如果想防止二次扩容可以使用实际参数数量 / 负载系数(默认0.75) + 1.

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/**
  * Implements Map.put and related methods
  *
  * @param hash hash for key
  * @param key the key
  * @param value the value to put
  * @param onlyIfAbsent if true, don't change existing value
  * @param evict if false, the table is in creation mode.
  * @return previous value, or null if none
  */
final V putVal(int hash, K key, V value, boolean onlyIfAbsent,
                boolean evict) {
    Node<K,V>[] tab; Node<K,V> p; int n, i;
    if ((tab = table) == null || (n = tab.length) == 0)
        n = (tab = resize()).length;
    if ((p = tab[i = (n - 1) & hash]) == null)
        tab[i] = newNode(hash, key, value, null);
    else {
        Node<K,V> e; K k;
        if (p.hash == hash &&
            ((k = p.key) == key || (key != null && key.equals(k))))
            e = p;
        else if (p instanceof TreeNode)
            e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);
        else {
            for (int binCount = 0; ; ++binCount) {
                if ((e = p.next) == null) {
                    p.next = newNode(hash, key, value, null);
                    if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st
                        treeifyBin(tab, hash);
                    break;
                }
                if (e.hash == hash &&
                    ((k = e.key) == key || (key != null && key.equals(k))))
                    break;
                p = e;
            }
        }
        if (e != null) { // existing mapping for key
            V oldValue = e.value;
            if (!onlyIfAbsent || oldValue == null)
                e.value = value;
            afterNodeAccess(e);
            return oldValue;
        }
    }
    ++modCount;
    if (++size > threshold)
        resize();
    afterNodeInsertion(evict);
    return null;
}

final Node<K,V>[] resize() {
    Node<K,V>[] oldTab = table;
    int oldCap = (oldTab == null) ? 0 : oldTab.length;
    int oldThr = threshold;
    int newCap, newThr = 0;
    if (oldCap > 0) {
        if (oldCap >= MAXIMUM_CAPACITY) {
            threshold = Integer.MAX_VALUE;
            return oldTab;
        }
        else if ((newCap = oldCap << 1) < MAXIMUM_CAPACITY &&
                  oldCap >= DEFAULT_INITIAL_CAPACITY)
            newThr = oldThr << 1; // double threshold
    }
    else if (oldThr > 0) // initial capacity was placed in threshold
        newCap = oldThr;
    else {               // zero initial threshold signifies using defaults
        newCap = DEFAULT_INITIAL_CAPACITY;
        newThr = (int)(DEFAULT_LOAD_FACTOR * DEFAULT_INITIAL_CAPACITY);
    }
    if (newThr == 0) {
        float ft = (float)newCap * loadFactor;
        newThr = (newCap < MAXIMUM_CAPACITY && ft < (float)MAXIMUM_CAPACITY ?
                  (int)ft : Integer.MAX_VALUE);
    }
    threshold = newThr;
    @SuppressWarnings({"rawtypes","unchecked"})
        Node<K,V>[] newTab = (Node<K,V>[])new Node[newCap];
    table = newTab;
    if (oldTab != null) {
        for (int j = 0; j < oldCap; ++j) {
            Node<K,V> e;
            if ((e = oldTab[j]) != null) {
                oldTab[j] = null;
                if (e.next == null)
                    newTab[e.hash & (newCap - 1)] = e;
                else if (e instanceof TreeNode)
                    ((TreeNode<K,V>)e).split(this, newTab, j, oldCap);
                else { // preserve order
                    Node<K,V> loHead = null, loTail = null;
                    Node<K,V> hiHead = null, hiTail = null;
                    Node<K,V> next;
                    do {
                        next = e.next;
                        if ((e.hash & oldCap) == 0) {
                            if (loTail == null)
                                loHead = e;
                            else
                                loTail.next = e;
                            loTail = e;
                        }
                        else {
                            if (hiTail == null)
                                hiHead = e;
                            else
                                hiTail.next = e;
                            hiTail = e;
                        }
                    } while ((e = next) != null);
                    if (loTail != null) {
                        loTail.next = null;
                        newTab[j] = loHead;
                    }
                    if (hiTail != null) {
                        hiTail.next = null;
                        newTab[j + oldCap] = hiHead;
                    }
                }
            }
        }
    }
    return newTab;
}

总结

如果想防止二次扩容可以使用此算法: 实际参数数量 / 负载系数(默认0.75) + 1.

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Maven Findbugs 插件使用

什么是 Findbugs

Findbugs是使用静态分析查找Java代码中的错误的程序

pom 依赖

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<plugins>
    <plugin>
        <groupId>org.codehaus.mojo</groupId>
        <artifactId>findbugs-maven-plugin</artifactId>
        <version>2.5.2</version>
    </plugin>
</plugins>

命令

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mvn clean compile findbugs:findbugs findbugs:gui

执行这条命令

  1. 清理 target 目录
  2. 编译 class
  3. 生成 findbugs 文件
  4. 执行 findbugs gui 程序，查看问题

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基于JMS 远程分区的 spring batch

关于 spring batch 的应用场景

通常做法

在支付系统中避免不了每天的交易结算，我们通常这样做，定时每天读取所有需要处理的交易记录，然后 for 循环处理，数据量小业务逻辑简单这样做没什么问题。如果业务复杂,就不能这么简单处理了，后期代码维护将是一个大问题。当数据量大了读取所有数据再处理也是行不通的，大量数据不可能一次全部读取到内存中，数据量大单台机处理也会很缓慢。

思考解决方案

这里可能会考虑到分批次多进程多线程处理，大致方案是读取所有需要处理数据的key，发送到mq，多台机器消费处理。

spring batch 来解决

spring batch 介绍 可以在官方文档看看，鉴于上面的场景，在 step read 前读取所有 key，然后拆分，拆分数量可以根据部署消费者数量定义，分区之后发送到mq，消费者接收到需要处理的 key 后，本地再拆分多线程处理，大致方案就是这样。

一张图来理解

jms-batch
这里 主 定义为 M, 从 定义为 S.
调度系统发送一条起批消息，哪台先抢到消费，哪台就是 M（注意：这种模式即是M也是S，除非明确指定了某一台来起批，不去监听 S 队列）。M 启动 job 执行分区逻辑，通过mq分发 key 到 S(本身 M 也监听了，所以 M 也是 S), S 收到消息执行业务逻辑（也可本地分片多线程处理），S执行完回复消息，或者 M 到数据库轮训结果。批量结束。

一个简单的demo batch-demo

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迭代器(Iterator)

提供按顺序访问聚合对象的元素，并不暴露聚合对象的内部表示。

java 代码

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public interface Iterator<T> {

	boolean hasNext();

	T next();
}


public class ConcreteIterator<Item> implements Iterator<Item> {

	private Item[] items;
	private int position = 0;

	public ConcreteIterator(Item[] items) {
		this.items = items;
	}

	@Override
	public boolean hasNext() {
		return position < items.length;
	}

	@Override
	public Item next() {
		return items[position++];
	}
}

public class IteratorTest {

	public static void main(String[] args) {
		Integer[] items = new Integer[10];
		for (int i = 0; i < items.length; i++) {
			items[i] = i;
		}
		Iterator<Integer> iterator = new ConcreteIterator<>(items);
		while (iterator.hasNext()) {
			System.out.println(iterator.next());
		}
	}
}