Reading Day
try-with-resources是jdk1.7引入的语法，使得关闭资源操作无需层层嵌套在finally
当try-finally关闭资源时，其出现了两处异常，往往只会返回第一处异常。
当java7开始引入try-with-resources后，这些问题就迎刃而解了。不过使用这个结构的时候，必须接入AutoCloseable接口
其中包括了单个返回void的close方法。现在Java库与第三方类库中的许多类和接口都实现了或拓展了AutoCloseable接口
Try-Catch-Finally 结构
可见，我们需要手动关闭两个Stream资源。而且为了防止异常的产生而无法关闭，需要借助finally正常关闭资源
public class DemoTest {
public static void main(String[] args) {
BufferedInputStream bin = null;
BufferedOutputStream bout = null;
try {
bin = new BufferedInputStream(new FileInputStream(new File("test.txt")));
bout = new BufferedOutputStream(new FileOutputStream(new File("out.txt")));
int b;
while ((b = bin.read()) != -1) {
bout.write(b);
}
}
catch (IOException e) {
e.printStackTrace();
}
finally {
if (bin != null) {
try {
bin.close();
}
catch (IOException e) {
throw e;
}
finally {
if (bout != null) {
try {
bout.close();
}
catch (IOException e) {
throw e;
}
}
}
}
}
}
}
Try-with-resources结构
而在try-with-resources中，我们只需要这样，编译器会帮我们自动补全close()，并且还会将异常正确报出，而不会由于嵌
套只指出一处异常。
public class TryWithResource {
public static void main(String[] args) {
try (BufferedInputStream bin = new BufferedInputStream(new FileInputStream(new File("test.txt")));
BufferedOutputStream bout = new BufferedOutputStream(new FileOutputStream(new File("out.txt")))) {
int b;
while ((b = bin.read()) != -1) {
bout.write(b);
}
}catch (IOException e) {
e.printStackTrace();
}
}
}
反编译class , 可见close()的补全
public class TryWithResource {
public TryWithResource() {
}
public static void main(String[] args) {
try {
Connection conn = new Connection();
Throwable var2 = null;
try {
conn.sendData();
} catch (Throwable var12) {
var2 = var12;
throw var12;
} finally {
if (conn != null) {
if (var2 != null) {
try {
conn.close();
} catch (Throwable var11) {
var2.addSuppressed(var11);
}
} else {
conn.close();
}
}
}
} catch (Exception var14) {
var14.printStackTrace();
}
}
}