JDK7特性：try-with-resources与AutoCloseable接口（实践）

1.正常写法 代码：

public class AutoCloseableDemo {
	public static void main(String[] args) {
		try (AutoCloseableObjecct app = new AutoCloseableObjecct()) {
			System.out.println("--try--");
		} catch (Exception e) {
			System.out.println("--catch--");
		} finally {
			System.out.println("--finally--");
		}
	}
	public static class AutoCloseableObjecct implements AutoCloseable {
		@Override
		public void close() throws Exception {
			System.out.println("AutoCloseable.close");
		}
	}
}

结果：实现AutoCloseable结果，会在执行try之后,finally之前，调用对象的close方法

--try--
AutoCloseable.close
--finally--

2.try中有异常 代码：

import java.io.IOException;
public class AutoCloseableDemo {
	public static void main(String[] args) {
		try (AutoCloseableObjecct app = new AutoCloseableObjecct()) {
			System.out.println("--try--");
			throw new IOException();
		} catch (Exception e) {
			System.out.println("--catch--");
		} finally {
			System.out.println("--finally--");
		}
	}
	public static class AutoCloseableObjecct implements AutoCloseable {
		@Override
		public void close() throws Exception {
			System.out.println("AutoCloseable.close");
		}
	}
}

结果：有异常的情况，还是会自动关闭。调用close是在try 执行之后，catch,finally执行之前。

--try--
AutoCloseable.close
--catch--
--finally--

3.如果 close出现异常，会怎么样，代码：

import java.io.IOException;

public class AutoCloseableDemo {
	public static void main(String[] args) {
		try (AutoCloseableObjecct app1 = new AutoCloseableObjecct()) {
			System.out.println("--try--");
		} catch (Exception e) {
			System.out.println("--catch--" + e);
		} finally {
			System.out.println("--finally--");
		}
	}

	public static class AutoCloseableObjecct implements AutoCloseable {
		@Override
		public void close() throws Exception {
			System.out.println(" AutoCloseable.close");
			throw new IOException("AutoCloseable close Exception");
		}
	}
}

结果：如果 close出现异常会被catch块捕获到异常。无catch或者catch无捕获到异常（即异常不匹配的），会向外抛出。

--try--
 AutoCloseable.close
--catch--java.io.IOException: AutoCloseable close Exception
--finally--

4.多资源情况 代码：

public class AutoCloseableDemo {
	public static void main(String[] args) {
		try (AutoCloseableObjecct app1 = new AutoCloseableObjecct();
				AutoCloseableObjecct app2 = new AutoCloseableObjecct();
				AutoCloseableObjecct app3 = new AutoCloseableObjecct()) {
			System.out.println("--try--");
		} catch (Exception e) {
			System.out.println("--catch--");
		} finally {
			System.out.println("--finally--");
		}
	}

	public static class AutoCloseableObjecct implements AutoCloseable {
		@Override
		public void close() throws Exception {
			System.out.println(this + " AutoCloseable.close");
		}
	}
}

结果：多资源的引用，用；分号隔开

--try--
AutoCloseableDemo$AutoCloseableObjecct@7fbe847c AutoCloseable.close
AutoCloseableDemo$AutoCloseableObjecct@41975e01 AutoCloseable.close
AutoCloseableDemo$AutoCloseableObjecct@c2e1f26 AutoCloseable.close
--finally--

5.多资源close都出现异常，代码：

import java.io.IOException;

public class AutoCloseableDemo {
	public static void main(String[] args) {
		try (AutoCloseableObjecct app1 = new AutoCloseableObjecct("app1");
				AutoCloseableObjecct app2 = new AutoCloseableObjecct("app2");
				AutoCloseableObjecct app3 = new AutoCloseableObjecct("app3");) {
			System.out.println("--try--");
		} catch (Exception e) {
			System.out.println("--catch--" + e);
		} finally {
			System.out.println("--finally--");
		}
	}

	public static class AutoCloseableObjecct implements AutoCloseable {
		String name;

		public AutoCloseableObjecct(String name) {
			super();
			this.name = name;
		}

		@Override
		public void close() throws Exception {
			System.out.println(name + " AutoCloseable.close");
			throw new IOException(name + " AutoCloseable close Exception");
		}
	}
}

结果：多资源的都出现异常的情况，close都会执行。close的执行顺序和声明顺序相反。catch捕获到的异常时最先出现异常的close。

--try--
app3 AutoCloseable.close
app2 AutoCloseable.close
app1 AutoCloseable.close
--catch--java.io.IOException: app3 AutoCloseable close Exception
--finally--

6.检验try，catch，finally中 对资源的使用：try块中可以正常使用，catch块和finally块不行

7.检验非try-with-resources 的AutoCloseable实现实例是否会自动关闭：

public class AutoCloseableDemo {
	public static void main(String[] args) {
		AutoCloseableObjecct app2 = new AutoCloseableObjecct("app2");
		try (AutoCloseableObjecct app1 = new AutoCloseableObjecct("app1")) {
			System.out.println("--try--");
		} catch (Exception e) {
			System.out.println("--catch--");
		} finally {
			System.out.println("--finally--");
		}
	}
	public static class AutoCloseableObjecct implements AutoCloseable {
		String name;
		public AutoCloseableObjecct(String name) {
			super();
			this.name = name;
		}
		@Override
		public void close() throws Exception {
			System.out.println(name + " AutoCloseable.close");
		}
	}
}

结果：只有在try-with-resources 中，且实现AutoCloseable，才会自动关闭。

           对于实现AutoCloseable的类的实例，可以不放try-with-resources中，从而自己实现关闭资源（在需要自己定制关闭资源的时候）。

--try--
app1 AutoCloseable.close
--finally--

8.Cloasable的源码：实现Cloasable就实现了AutoCloseable，since 1.5，而流基本都实现了Cloasable接口

package java.io;

import java.io.IOException;

/**
 * A {@code Closeable} is a source or destination of data that can be closed.
 * The close method is invoked to release resources that the object is
 * holding (such as open files).
 *
 * @since 1.5
 */
public interface Closeable extends AutoCloseable {

9.总结

• Cloasable接口 继承AutoCloseable，自JDK1.5开始。
• try-with-resources与AutoCloseable的close执行顺序，try-close-catch-finally
• 多资源用分号隔开，执行close的顺序为后声明的先执行；
• 多资源close异常，不论前面close是否出现异常，后面的close一定会执行，异常抛出只能捕获最先执行close错误的异常。