概述

MoreSuppliers类是一个Java工具类，它提供了一些增强的Supplier函数，使得Supplier执行的结果可以被缓存，真正的调用只执行一次。

public static <T> CloseableSupplier<T> lazy(Supplier<T> delegate)：

这个方法返回一个懒加载的提供器，首次获取值时通过delegate加载值，并缓存这个值，在后续获取时直接返回这个缓存的值。这个方法的使用场景是当你有一个计算成本较高或者IO操作的Supplier，并且你希望只执行一次这个操作，然后缓存结果以供后续使用。

示例：

Supplier<String> expensiveOperation = () -> {// Some expensive operation...return "result";};Supplier<String> lazySupplier = MoreSuppliers.lazy(expensiveOperation);String result = lazySupplier.get();  // The expensive operation is performed here.String cachedResult = lazySupplier.get();  // The cached result is returned here.

public static <T> CloseableSupplier<T> lazy(Supplier<T> delegate, boolean resetAfterClose)：

这个方法和上一个方法类似，但是它允许在关闭提供器返回的资源后，是否释放缓存的对象。这个方法的使用场景是当你的Supplier返回的是一个需要关闭的资源，比如一个数据库连接，你希望在关闭这个资源后，下次调用get()方法时重新获取一个新的资源。

示例：

Supplier<Connection> connectionSupplier = () -> {// Get a connection from the database...return connection;};CloseableSupplier<Connection> lazySupplier = MoreSuppliers.lazy(connectionSupplier, true);Connection connection = lazySupplier.get();  // The connection is obtained here.lazySupplier.tryClose(Connection::close);  // The connection is closed here.Connection newConnection = lazySupplier.get();  // A new connection is obtained here.

public static <T, X extends Throwable> CloseableThrowableSupplier<T, X> lazyEx(ThrowableSupplier<T, X> delegate)：

这个方法返回一个懒加载的提供器，支持异常类型声明。这个方法的使用场景是当你的Supplier可能抛出一个异常，你希望这个异常能被正确地传播出去。

示例：

ThrowableSupplier<String, IOException> ioOperation = () -> {// Some IO operation...return "result";};ThrowableSupplier<String, IOException> lazySupplier = MoreSuppliers.lazyEx(ioOperation);try {String result = lazySupplier.get();  // The IO operation is performed here.} catch (IOException e) {// Handle the exception...}

public static <T, X extends Throwable> CloseableThrowableSupplier<T, X> lazyEx(ThrowableSupplier<T, X> delegate, boolean resetAfterClose)：

这个方法和上一个方法类似，但是它允许在关闭提供器返回的资源后，是否释放缓存的对象。这个方法的使用场景是当你的Supplier返回的是一个需要关闭的资源并且可能抛出一个异常，你希望在关闭这个资源后，下次调用get()方法时重新获取一个新的资源，并且异常能被正确地传播出去。

示例：

ThrowableSupplier<Connection, SQLException> connectionSupplier = () -> {// Get a connection from the database...return connection;};CloseableThrowableSupplier<Connection, SQLException> lazySupplier = MoreSuppliers.lazyEx(connectionSupplier, true);try {Connection connection = lazySupplier.get();  // The connection is obtained here.lazySupplier.tryClose(Connection::close);  // The connection is closed here.Connection newConnection = lazySupplier.get();  // A new connection is obtained here.} catch (SQLException e) {// Handle the exception...}

public static <T> AsyncSupplier<T> asyncLazyEx(Supplier<T> delegate, Supplier<T> pendingSupplier, String threadName)：

这个方法返回一个异步加载的提供器，通过异步线程来完成初始化操作，支持超时。当超过指定的时间没有获取初始值成功时，使用pendingSupplier提供的值作为托底。这个方法的使用场景是当你的Supplier需要花费较长的时间来获取值，你希望这个操作能在一个单独的线程中进行，而主线程可以继续执行其他任务。

示例：

Supplier<String> slowOperation = () -> {// Some slow operation...return "result";};Supplier<String> fallback = () -> "fallback";AsyncSupplier<String> asyncSupplier = MoreSuppliers.asyncLazyEx(slowOperation, fallback, "InitThread");String result = asyncSupplier.get(Duration.ofSeconds(5));  // The slow operation is performed in a separate thread. If it takes more than 5 seconds, the fallback value is returned.

public static <T> AsyncSupplier<T> asyncLazyEx(Supplier<T> delegate, String threadName)：

这个方法和上一个方法类似，但是它没有提供托底的Supplier，如果异步初始化值超时，它将返回null。

示例：

Supplier<String> slowOperation = () -> {// Some slow operation...return "result";};AsyncSupplier<String> asyncSupplier = MoreSuppliers.asyncLazyEx(slowOperation, "InitThread");String result = asyncSupplier.get(Duration.ofSeconds(5));  // The slow operation is performed in a separate thread. If it takes more than 5 seconds, null is returned.

public static <T> AsyncSupplier<T> asyncLazyEx(Supplier<T> delegate)：

这个方法和上一个方法类似，但是它没有指定执行初始化操作的线程名称。

示例：

Supplier<String> slowOperation = () -> {// Some slow operation...return "result";};AsyncSupplier<String> asyncSupplier = MoreSuppliers.asyncLazyEx(slowOperation);String result = asyncSupplier.get(Duration.ofSeconds(5));  // The slow operation is performed in a separate thread. If it takes more than 5 seconds, null is returned.

CloseableSupplier<T>：

这是一个可关闭的Supplier实现，支持通过tryClose(ThrowableConsumer<T, X>closer)方法关闭提供器返回的资源。

示例：

CloseableSupplier<Connection> connectionSupplier = MoreSuppliers.lazy(() -> {// Get a connection from the database...return connection;}, true);Connection connection = connectionSupplier.get();  // The connection is obtained here.connectionSupplier.tryClose(Connection::close);  // The connection is closed here.

CloseableThrowableSupplier<T, X>：

这是一个可关闭的Supplier实现，支持异常类型声明，通过tryClose(ThrowableConsumer<T, X> closer)方法关闭提供器返回的资源。

示例：

CloseableThrowableSupplier<Connection, SQLException> connectionSupplier = MoreSuppliers.lazyEx(() -> {// Get a connection from the database...return connection;}, true);try {Connection connection = connectionSupplier.get();  // The connection is obtained here.connectionSupplier.tryClose(Connection::close);  // The connection is closed here.} catch (SQLException e) {// Handle the exception...}

AsyncSupplier<T>：

这是一个异步加载的Supplier实现，通过异步线程来完成初始化操作，支持超时。当超过指定的时间没有获取初始值成功时，使用pendingSupplier提供的值作为托底。

示例：

Supplier<String> slowOperation = () -> {// Some slow operation...return "result";};Supplier<String> fallback = () -> "fallback";AsyncSupplier<String> asyncSupplier = MoreSuppliers.asyncLazyEx(slowOperation, fallback, "InitThread");String result = asyncSupplier.get(Duration.ofSeconds(5));  // The slow operation is performed in a separate thread. If it takes more than 5 seconds, the fallback value is returned.

参考：

https://github.com/PhantomThief/more-lambdas-java/blob/master/core/src/main/java/com/github/phantomthief/util/MoreSuppliers.java