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文章目录

线程池工具类封装(高级版)

银河小徐
2022-02-20 / 0 评论 / 19 点赞 / 384 阅读 / 19,966 字 / 正在检测是否收录...
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为什么需要一个线程池工具类?

整个项目,用到线程执行任务的地方很多,不可能哪里用到就在那里直接 new 一个线程执行,这样资源得不到重复利用,一旦线程过多就会导致内存不足。

线程池的好处是什么?

使用线程池执行线程任务,当一个线程执行完成一个任务之后,线程资源回到线程池,资源得到重复利用。

线程池为什么使用自定义方式?

因为 java 自带线程池都会有可能造成内存不足的问题。自定义线程池,根据服务器配置定制线程池核心线程、最大线程等,是最好的方式。

我封装的线程池工具类有什么好处?

  • 扩展性高
  • 可注解形式实现执行
  • 可根据业务需要注册不同的线程池,区分业务模块使用
  • 可以执行无返回值线程任务,可以执行有返回值的线程任务。

代码实现

创建一个线程任务类

该类主要用来承接 Runnable 方法,和其他业务相关需要的参数。

package com.scaffolding.example.threads;

import com.scaffolding.example.threads.aop.Pooled;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.concurrent.Callable;
import java.util.concurrent.Executors;

/**
 * 需要执行的线程任务
 *
 * @author XiaoXuxuy
 * @date 2022/2/20 14:32
 */
@Data
@NoArgsConstructor
@AllArgsConstructor
public class Worker<T> implements Runnable {

    private static final Logger LOGGER = LoggerFactory.getLogger(Worker.class);

    // 默认超时时间
    private static final long DEFAULT_TIMEOUT = 500;

    // 执行指令
    private Runnable command;

    // 返回结果
    private Result<T> result = new Result<>();

    // 超时
    private long timeout;

    // 策略
    private Pooled.PoolOverAct poolOverAct = Pooled.PoolOverAct.REJECT;

    // 预备执行时间
    private volatile long prepareExecutionTime;

    // 开始执行时间
    private volatile long startExecutionTime;

    // 结束执行时间
    private volatile long endExecutionTime;

    // 执行的线程池名称
    private String executorName;

    public Worker(Runnable command) {
        this.command = command;
        this.timeout = DEFAULT_TIMEOUT;
    }

    public Worker(Runnable command, Pooled.PoolOverAct poolOverAct) {
        this.command = command;
        this.timeout = DEFAULT_TIMEOUT;
        this.poolOverAct = poolOverAct;
    }

    public Worker(Runnable command, T result) {
        this.command = command;
        this.result = new Result<>(result);
        this.timeout = DEFAULT_TIMEOUT;
    }

    public Worker(Runnable command, T result, long timeout) {
        this.command = command;
        this.result = new Result<>(result);
        this.timeout = timeout;
    }

    @Override
    public void run() {
        startExecution();
        try {
            command.run();
        } finally {
            endExecution();
        }
    }

    /**
     * 开始执行(预备执行耗时)
     */
    private void startExecution() {
        this.startExecutionTime = System.currentTimeMillis();
        LOGGER.info("POOL_DISPATCH_TIME, EXECUTOR: {}, TIME: {} ms", this.executorName, this.getPrepareTime());
    }

    /**
     * 结束执行(执行耗时)
     */
    private void endExecution() {
        this.endExecutionTime = System.currentTimeMillis();
        LOGGER.info("POOL_EXECUTE_TIME, EXECUTOR: {}, TIME: {} ms", this.executorName, this.getExecutionTime());
    }

    /**
     * 预备耗时
     *
     * @return
     */
    public long getPrepareTime() {
        return this.startExecutionTime - this.prepareExecutionTime;
    }

    /**
     * 执行耗时
     *
     * @return
     */
    public long getExecutionTime() {
        return this.endExecutionTime - this.startExecutionTime;
    }

    /**
     * callable执行线程
     *
     * @return
     */
    public Callable<Result<T>> callable() {
        return Executors.callable(command, result);
    }

    public void setResult(T result) {
        if (null != this.result) {
            this.result.value = result;
        }
    }

}

定义一个泛型结果类

承接具有执行结果的线程任务

package com.scaffolding.example.threads;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

/**
 * 线程结果
 *
 * @author XiaoXuxuy
 * @date 2022/2/20 14:33
 */
@Data
@NoArgsConstructor
@AllArgsConstructor
public class Result<T> {
    public T value;
}

定义线程池

package com.scaffolding.example.threads;

import lombok.Data;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.concurrent.*;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * 任务线程池
 *
 * @author XiaoXuxuy
 * @date 2022/2/19 19:34
 */
@Data
public class TaskToolExecutor {

    private static final Logger LOGGER = LoggerFactory.getLogger(TaskToolExecutor.class);

    /**
     * 默认核心线程数
     */
    private static final int DEFAULT_CORE_SIZE = 20;

    /**
     * 默认最大线程数
     */
    private static final int DEFAULT_MAX_SIZE = 50;

    /**
     * 默认空闲线程存活时间
     */
    private static final long DEFAULT_ALIVE_TIME = 60;

    /**
     * 默认队列数量
     */
    private static final int DEFAULT_QUEUE_SIZE = 1024;

    /**
     * 线程池
     */
    private ExecutorService pool;

    /**
     * 线程工厂
     */
    private ThreadFactory threadFactory;

    /**
     * 任务较多时暂存队列
     */
    private BlockingQueue<Runnable> workQueue;

    /**
     * 核心线程数
     */
    private int coreSize;

    /**
     * 最大线程数
     */
    private int maxSize;

    /**
     * 空闲线程存活时间
     */
    private long aliveTime;

    /**
     * 队列数量
     */
    private int queueSize;

    /**
     * 线程池名称
     */
    private String name;

    /**
     * 初始化线程池
     */
    public void init() {
        if (null == pool) {

            if (null == workQueue) {
                queueSize = queueSize > 0 ? queueSize : DEFAULT_QUEUE_SIZE;
                workQueue = new LinkedBlockingQueue<>(queueSize);
            }
            if (null == threadFactory) {
                threadFactory = TaskToolExecutor.defaultThreadFactory();
            }

            coreSize = coreSize > 0 ? coreSize : DEFAULT_CORE_SIZE;
            maxSize = maxSize > 0 ? maxSize : DEFAULT_MAX_SIZE;
            aliveTime = aliveTime > 0 ? aliveTime : DEFAULT_ALIVE_TIME;
            pool = new ThreadPoolExecutor(coreSize, maxSize, aliveTime, TimeUnit.SECONDS, workQueue, threadFactory);
        }
    }

    /**
     * 销毁线程池
     */
    public void destroy() {
        this.pool.shutdown();
    }

    /**
     * 执行Task
     *
     * @param worker
     */
    public void execute(Worker<?> worker) {
        try {
            worker.setExecutorName(this.name);
            worker.setPrepareExecutionTime(System.currentTimeMillis());
            pool.execute(worker);
        } catch (RejectedExecutionException e) {
            // 拒绝策略
            dealWhenPoolFull(worker, e);
        }
    }

    /**
     * 提交Task,可获取线程返回结果
     *
     * @param worker
     * @param <T>
     * @return
     */
    public <T> T submit(Worker<T> worker) {
        try {
            Future<Result<T>> future = pool.submit(worker.callable());
            Result<T> result = future.get(worker.getTimeout(), TimeUnit.MILLISECONDS);
            return result.value;
        } catch (RejectedExecutionException e) {
            LOGGER.error("Rejected worker: Perhaps thread pool is full!", e);
        } catch (InterruptedException e) {
            LOGGER.error("Interrupted worker:", e);
        } catch (ExecutionException e) {
            LOGGER.error("Attempting to retrieve the result of a task that aborted!", e);
        } catch (TimeoutException e) {
            LOGGER.error("Timeout worker: get result timeout", e);
        }
        return worker.getResult().value;
    }

    /**
     * 线程池占满之后拒绝策略
     *
     * @param worker
     * @param e
     */
    private void dealWhenPoolFull(Worker<?> worker, RejectedExecutionException e) {
        switch (worker.getPoolOverAct()) {
            case REJECT:
                LOGGER.error("Rejected worker: Perhaps thread pool is full!", e);
                break;
            case RUN:
                worker.run();
                break;
            case BLOCK:
                try {
                    workQueue.put(worker);
                } catch (InterruptedException interruptedException) {
                    LOGGER.error("queue put worker: Perhaps block queue is full!", e);
                }
                break;
            case NEW_THREAD:
                Thread newThreadOutOfPool = threadFactory.newThread(worker);
                newThreadOutOfPool.setName("outOfPool-" + newThreadOutOfPool.getName());
                newThreadOutOfPool.start();
                break;
            default:
                LOGGER.error("Rejected worker: Perhaps thread pool is full!", e);
                break;
        }
    }

    /**
     * 默认线程工厂
     */
    static class DefaultThreadFactory implements ThreadFactory {
        static final AtomicInteger poolNumber = new AtomicInteger(1);
        final ThreadGroup group;
        final AtomicInteger threadNumber = new AtomicInteger(1);
        final String namePrefix;

        DefaultThreadFactory() {
            SecurityManager s = System.getSecurityManager();
            group = (s != null) ? s.getThreadGroup() : Thread.currentThread().getThreadGroup();
            namePrefix = "taskTool-" + poolNumber.getAndIncrement() + "-thread-";
        }

        @Override
        public Thread newThread(Runnable runnable) {
            Thread thread = new Thread(group, runnable, namePrefix + threadNumber.getAndIncrement(), 0);
            // 守护线程
            if (thread.isDaemon())
                thread.setDaemon(false);
            // 线程优先级
            if (thread.getPriority() != Thread.NORM_PRIORITY)
                thread.setPriority(Thread.NORM_PRIORITY);
            return thread;
        }
    }

    public static ThreadFactory defaultThreadFactory() {
        return new DefaultThreadFactory();
    }

    public void setQueueSize(int queueSize) {
        if (queueSize <= 0) {
            this.queueSize = DEFAULT_QUEUE_SIZE;
        } else {
            this.queueSize = queueSize;
        }
    }

}

项目启动初始化不同业务线程池

package com.scaffolding.example.threads;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

/**
 * 注册各种业务线程池
 *
 * @author XiaoXuxuy
 * @date 2022/2/19 20:17
 */
@Configuration
public class ExecutorPoolConfig {

    /**
     * 工具类线程池
     *
     * @return
     */
    @Bean(initMethod = "init", destroyMethod = "destroy")
    public TaskToolExecutor ciToolExecutor() {
        TaskToolExecutor ciToolExecutor = new TaskToolExecutor();
        ciToolExecutor.setName("ciToolExecutor");
        ciToolExecutor.setCoreSize(15);
        ciToolExecutor.setMaxSize(32);
        ciToolExecutor.setQueueSize(1024);
        return ciToolExecutor;
    }

    /**
     * 消息通知类线程池
     *
     * @return
     */
    @Bean(initMethod = "init", destroyMethod = "destroy")
    public TaskToolExecutor msgExecutor() {
        TaskToolExecutor msgExecutor = new TaskToolExecutor();
        msgExecutor.setName("msgExecutor");
        msgExecutor.setCoreSize(15);
        msgExecutor.setMaxSize(32);
        msgExecutor.setQueueSize(1024);
        return msgExecutor;
    }

}

测试

测试类

我们建一个测试类,测试无结果线程执行和有结果线程执行。

package com.scaffolding.example.threads;

import com.scaffolding.example.threads.aop.Pooled;
import junit.framework.TestCase;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.context.annotation.EnableAspectJAutoProxy;
import org.springframework.test.context.junit4.SpringRunner;

import java.util.Map;
import java.util.concurrent.CountDownLatch;

/**
 * @author Admin
 * @date 2022/2/20 15:16
 */
@RunWith(SpringRunner.class)
@SpringBootTest
@EnableAspectJAutoProxy(exposeProxy = true)
public class TaskToolExecutorTest extends TestCase {

    @Autowired
    private Map<String, TaskToolExecutor> executorMap;

    /**
     * 测试无返回结果线程
     */
    @Test
    public void testDispatchTask() {
        TaskToolExecutor executor = executorMap.get("ciToolExecutor");

        final CountDownLatch countDownLatch = new CountDownLatch(3);

        for (int i = 0; i < 3; i++) {
            Worker<Object> worker = createTestWorker(i, countDownLatch);
            executor.execute(worker);
        }

        try {
            countDownLatch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        System.out.println("所有线程执行完毕!");
    }

    private Worker<Object> createTestWorker(int i, CountDownLatch countDownLatch) {
        return new Worker<>(new Thread(() -> {
            System.out.println("我是任务" + i);
            countDownLatch.countDown();
        }), Pooled.PoolOverAct.NEW_THREAD);
    }

    /**
     * 测试有返回结果线程
     */
    @Test
    public void testHasResultTask() {
        TaskToolExecutor executor = executorMap.get("ciToolExecutor");

        final CountDownLatch countDownLatch = new CountDownLatch(1);

        Worker<Object> worker = createHasResultTestWorker(countDownLatch);
        Object result = executor.submit(worker);

        try {
            countDownLatch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        System.out.println("线程执行返回结果为: " + result);
    }

    private Worker<Object> createHasResultTestWorker(CountDownLatch countDownLatch) {
        Worker<Object> worker = new Worker<>();
        Runnable runnable = () -> {
            int count = 1;
            // 设置返回值
            worker.setResult(count);
            countDownLatch.countDown();
        };
        worker.setTimeout(500);
        worker.setCommand(runnable);
        return worker;
    }

}

测试结果

无返回值情况:

2022-02-20 17:52:43 INFO POOL_DISPATCH_TIME, EXECUTOR: ciToolExecutor, TIME: 1 ms
2022-02-20 17:52:43 INFO POOL_DISPATCH_TIME, EXECUTOR: ciToolExecutor, TIME: 0 ms
2022-02-20 17:52:43 INFO POOL_DISPATCH_TIME, EXECUTOR: ciToolExecutor, TIME: 1 ms
我是任务1
我是任务0
我是任务2
2022-02-20 17:52:43 INFO POOL_EXECUTE_TIME, EXECUTOR: ciToolExecutor, TIME: 0 ms
2022-02-20 17:52:43 INFO POOL_EXECUTE_TIME, EXECUTOR: ciToolExecutor, TIME: 0 ms
所有线程执行完毕!
2022-02-20 17:52:43 INFO POOL_EXECUTE_TIME, EXECUTOR: ciToolExecutor, TIME: 0 ms

有返回值情况:

线程执行返回结果为: 1

注解方式实现

定义一个注解

package com.scaffolding.example.threads.aop;

import java.lang.annotation.Retention;
import java.lang.annotation.Target;

import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.RetentionPolicy.RUNTIME;

/**
 * 线程池切面
 *
 * @author XiaoXuxuy
 * @date 2022/2/20 15:35
 */
@Target({METHOD})
@Retention(RUNTIME)
public @interface Pooled {

    boolean async() default true;

    long timeout() default 500;

    String executor() default "ciToolExecutor";

    PoolOverAct poolOverAct() default PoolOverAct.REJECT;

    enum PoolOverAct {
        REJECT, BLOCK, RUN, NEW_THREAD;
    }
}

定义一个Aop切面

package com.scaffolding.example.threads.aop;

import com.scaffolding.example.threads.TaskToolExecutor;
import com.scaffolding.example.threads.Worker;
import com.scaffolding.example.utils.PrimitiveUtils;
import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.reflect.MethodSignature;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.core.annotation.Order;
import org.springframework.stereotype.Component;

import java.util.Map;

/**
 * @author XiaoXuxuy
 * @date 2022/2/20 15:35
 */
@Aspect
@Component
@Order(AopOrder.POOLED_INVOKER_ORDER)
public class PooledInvoker {

    private static final Logger LOGGER = LoggerFactory.getLogger(PooledInvoker.class);

    @Autowired
    private Map<String, TaskToolExecutor> executorMap;

    @Around("@annotation(com.scaffolding.example.threads.aop.Pooled) && @annotation(pooled)")
    public Object around(final ProceedingJoinPoint pjp, Pooled pooled) {
        TaskToolExecutor executor = getExecutor(pooled.executor());
        Object result = null;
        Worker<Object> worker = toWorker(pjp);
        worker.setPoolOverAct(pooled.poolOverAct());
        if (pooled.async()) {
            executor.execute(worker);
        } else {
            worker.setTimeout(pooled.timeout());
            result = executor.submit(worker);
        }

        if (null == result) {
            Class<?> returnType = ((MethodSignature) pjp.getSignature()).getMethod().getReturnType();
            if (returnType.isPrimitive()) {
                return PrimitiveUtils.getPrimitiveDefaultValue(returnType);
            }
        }

        return result;
    }

    private Worker<Object> toWorker(ProceedingJoinPoint pjp) {
        final Worker<Object> worker = new Worker<>();
        Runnable command = () -> {
            try {
                worker.setResult(pjp.proceed());
            } catch (Throwable e) {
                LOGGER.error("Error pooled execute:", e);
            }
        };
        worker.setCommand(command);
        return worker;
    }

    private TaskToolExecutor getExecutor(String poolType) {
        return executorMap.get(poolType);
    }
}

使用方式

只要在方法加入 @Pooled 注解即可利用线程池执行该方法。

@Pooled(executor = "msgExecutor", poolOverAct = Pooled.PoolOverAct.NEW_THREAD)
public void notifyEmail() {
    System.out.println("我是通知线程");
}

附:Aop的拦截顺序定义

package com.scaffolding.example.threads.aop;

import org.springframework.core.Ordered;

/**
 * Aop的拦截顺序定义
 * POOLED_INVOKER_ORDER > DISTRIBUTED_LOCK_ORDER > 日志 > 事务
 *
 * @author XiaoXuxuy
 * @date 2022/2/20 15:38
 */
public class AopOrder {
    public static final int DISTRIBUTED_LOCK_ORDER = Ordered.HIGHEST_PRECEDENCE + 4;
    public static final int POOLED_INVOKER_ORDER = Ordered.HIGHEST_PRECEDENCE + 2;
}

附:Class原始类型工具类

package com.scaffolding.example.utils;

import java.util.Collection;
import java.util.Date;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

public class PrimitiveUtils {

	private static final ConcurrentMap<String, Class<?>>  NAME_CLASS_CACHE = new ConcurrentHashMap<String, Class<?>>();
	/**
	 * void(V).
	 */
	public static final char JVM_VOID = 'V';

	/**
	 * boolean(Z).
	 */
	public static final char JVM_BOOLEAN = 'Z';

	/**
	 * byte(B).
	 */
	public static final char JVM_BYTE = 'B';

	/**
	 * char(C).
	 */
	public static final char JVM_CHAR = 'C';

	/**
	 * double(D).
	 */
	public static final char JVM_DOUBLE = 'D';

	/**
	 * float(F).
	 */
	public static final char JVM_FLOAT = 'F';

	/**
	 * int(I).
	 */
	public static final char JVM_INT = 'I';

	/**
	 * long(J).
	 */
	public static final char JVM_LONG = 'J';

	/**
	 * short(S).
	 */
	public static final char JVM_SHORT = 'S';

	public static boolean isPrimitives(Class<?> cls) {
	    if (cls.isArray()) {
	        return isPrimitive(cls.getComponentType());
	    }
	    return isPrimitive(cls);
	}

	public static boolean isPrimitive(Class<?> cls) {
	    return cls.isPrimitive() || cls == String.class || cls == Boolean.class || cls == Character.class 
	            || Number.class.isAssignableFrom(cls) || Date.class.isAssignableFrom(cls);
	}

    public static boolean isPojo(Class<?> cls) {
        return ! isPrimitives(cls)
                && ! Collection.class.isAssignableFrom(cls) 
                && ! Map.class.isAssignableFrom(cls);
    }

	/**
	 * name to class.
	 * "boolean" => boolean.class
	 * "java.util.Map[][]" => java.util.Map[][].class
	 * 
	 * @param name name.
	 * @return Class instance.
	 */
	public static Class<?> name2class(String name) throws ClassNotFoundException
	{
		return name2class(getClassLoader(), name);
	}

	/**
	 * name to class.
	 * "boolean" => boolean.class
	 * "java.util.Map[][]" => java.util.Map[][].class
	 * 
	 * @param cl ClassLoader instance.
	 * @param name name.
	 * @return Class instance.
	 */
	private static Class<?> name2class(ClassLoader cl, String name) throws ClassNotFoundException
	{
		int c = 0, index = name.indexOf('[');
		if( index > 0 )
		{
			c = ( name.length() - index ) / 2;
			name = name.substring(0, index);
		}
		if( c > 0 )
		{
			StringBuilder sb = new StringBuilder();
			while( c-- > 0 )
				sb.append("[");

			if( "void".equals(name) ) sb.append(JVM_VOID);
			else if( "boolean".equals(name) ) sb.append(JVM_BOOLEAN);
			else if( "byte".equals(name) ) sb.append(JVM_BYTE);
			else if( "char".equals(name) ) sb.append(JVM_CHAR);
			else if( "double".equals(name) ) sb.append(JVM_DOUBLE);
			else if( "float".equals(name) ) sb.append(JVM_FLOAT);
			else if( "int".equals(name) ) sb.append(JVM_INT);
			else if( "long".equals(name) ) sb.append(JVM_LONG);
			else if( "short".equals(name) ) sb.append(JVM_SHORT);
			else sb.append('L').append(name).append(';'); // "java.lang.Object" ==> "Ljava.lang.Object;"
			name = sb.toString();
		} else {
			if( "void".equals(name) ) return void.class;
			else if( "boolean".equals(name) ) return boolean.class;
			else if( "byte".equals(name) ) return byte.class;
			else if( "char".equals(name) ) return char.class;
			else if( "double".equals(name) ) return double.class;
			else if( "float".equals(name) ) return float.class;
			else if( "int".equals(name) ) return int.class;
			else if( "long".equals(name) ) return long.class;
			else if( "short".equals(name) ) return short.class;
		}

		if( cl == null ){
			cl = getClassLoader();
		}
		Class<?> clazz = NAME_CLASS_CACHE.get(name);
        if(clazz == null){
            clazz = Class.forName(name, true, cl);
            NAME_CLASS_CACHE.put(name, clazz);
        }
        return clazz;
	}

	public static ClassLoader getClassLoader(){
		return getClassLoader(PrimitiveUtils.class);
	}

	/**
	 * get class loader 
	 * 
	 * @param cls
	 * @return class loader
	 */
    public static ClassLoader getClassLoader(Class<?> cls) {
    	ClassLoader cl = null;
        try {
            cl = Thread.currentThread().getContextClassLoader();
        } catch (Throwable ex) {
            // Cannot access thread context ClassLoader - falling back to system class loader...
        }
        if (cl == null) {
            // No thread context class loader -> use class loader of this class.
            cl = cls.getClassLoader();
        }
        return cl;
    }
  
    private static final Map<String, PrimitiveInfo<?>> PRIMITIVES = new HashMap<String, PrimitiveInfo<?>>();

    static {
        addPrimitive(boolean.class, "Z", Boolean.class, "booleanValue", false);
        addPrimitive(short.class, "S", Short.class, "shortValue", (short) 0);
        addPrimitive(int.class, "I", Integer.class, "intValue", 0);
        addPrimitive(long.class, "J", Long.class, "longValue", 0L);
        addPrimitive(float.class, "F", Float.class, "floatValue", 0F);
        addPrimitive(double.class, "D", Double.class, "doubleValue", 0D);
        addPrimitive(char.class, "C", Character.class, "charValue", '\0');
        addPrimitive(byte.class, "B", Byte.class, "byteValue", (byte) 0);
        addPrimitive(void.class, "V", Void.class, null, null);
    }

    private static <T> void addPrimitive(Class<T> type, String typeCode, Class<T> wrapperType, String unwrapMethod,
                                         T defaultValue) {
        PrimitiveInfo<T> info = new PrimitiveInfo<T>(type, typeCode, wrapperType, unwrapMethod, defaultValue);

        PRIMITIVES.put(type.getName(), info);
        PRIMITIVES.put(wrapperType.getName(), info);
    }

    /** 代表一个primitive类型的信息。 */
    @SuppressWarnings("unused")
    private static class PrimitiveInfo<T> {
        final Class<T> type;
        final String   typeCode;
        final Class<T> wrapperType;
        final String   unwrapMethod;
        final T        defaultValue;

        public PrimitiveInfo(Class<T> type, String typeCode, Class<T> wrapperType, String unwrapMethod, T defaultValue) {
            this.type = type;
            this.typeCode = typeCode;
            this.wrapperType = wrapperType;
            this.unwrapMethod = unwrapMethod;
            this.defaultValue = defaultValue;
        }
    }
  
    /**
     * 取得primitive类型的wrapper。如果不是primitive,则原样返回。
     * <p>
     * 例如:
     * <p/>
     * <pre>
     * ClassUtil.getPrimitiveWrapperType(int.class) = Integer.class;
     * ClassUtil.getPrimitiveWrapperType(int[].class) = int[].class;
     * ClassUtil.getPrimitiveWrapperType(int[][].class) = int[][].class;
     * ClassUtil.getPrimitiveWrapperType(String[][].class) = String[][].class;
     * </pre>
     * <p/>
     * </p>
     */
    @SuppressWarnings("unchecked")
    public static <T> Class<T> getWrapperTypeIfPrimitive(Class<T> type) {
        if (type.isPrimitive()) {
            return ((PrimitiveInfo<T>) PRIMITIVES.get(type.getName())).wrapperType;
        }

        return type;
    }
  
    /**
     * 取得primitive类型的默认值。如果不是primitive,则返回<code>null</code>。
     * <p>
     * 例如:
     * <p/>
     * <pre>
     * ClassUtil.getPrimitiveDefaultValue(int.class) = 0;
     * ClassUtil.getPrimitiveDefaultValue(boolean.class) = false;
     * ClassUtil.getPrimitiveDefaultValue(char.class) = '\0';
     * </pre>
     * <p/>
     * </p>
     */
    @SuppressWarnings("unchecked")
    public static <T> T getPrimitiveDefaultValue(Class<T> type) {
        PrimitiveInfo<T> info = (PrimitiveInfo<T>) PRIMITIVES.get(type.getName());

        if (info != null) {
            return info.defaultValue;
        }

        return null;
    }

}
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