你还在使用 try-catch-finally 关闭资源？
@author hetiantian
*/
public class Resource implements AutoCloseable {
public void sayHello() {
System.out.println("hello");
}
@Override
public void close() throws Exception {
System.out.println("Resource is closed");
}
}
测试类 CloseResourceIn7.java
/**
jdk7 及以后关闭流的方式
@author hetiantian
*/
public class CloseResourceIn7 {
public static void main
(String[] args) {
try(Resource resource = new Resource()) {
resource.sayHello();
} catch (Exception e) {
e.printStackTrace();
}
}
}
打印结果：
hello
Resource is closed
当存在多个打开资源的时候：资源二 Resource2.java
/**
资源 2
@author hetiantian
*/
public class Resource2 implements AutoCloseable {
public void sayhello() {
System.out.println("Resource say hello");
}
@Override
public void close() throws Exception {
System.out.println("Resource2 is closed");
}
}
测试类 CloseResourceIn7.java
/**
jdk7 及以后关闭流的方式
@author hetiantian
*/
public class CloseResourceIn7 {
public static void main(String[] args) {
try(Resource resource = new Resource(); Resource2 resource2 = new Resource2()) {
resource.sayHello();
resource2.sayhello();
} catch (Exception e) {
e.printStackTrace();
}
}
}
打印结果：
hello
Resource say hello
Resource2 is closed
Resource is closed
即使资源很多，代码也可以写的很简洁，如果用JDK7之前的方式去关闭资源，那么资源越多，用 fianl 关闭资源时嵌套也就越多。最近写的这篇：写了个全局变量的bug，也推荐看下。
那么它的底层原理又是怎样的呢，由皮皮甜独家揭秘优雅关闭资源背后的密码秘密
查看编译的 class 文件 CloseResourceIn7.class：
public class CloseResourceIn7 {
public CloseResourceIn7() {
}
public static void main(String[] args) {
try {
Resource resource = new Resource();
Throwable var2 = null;
try {
resource.sayHello();
} catch (Throwable var12) {
var2 = var12;
throw var12;
} finally {
if (resource != null) {
if (var2 != null) {
try {
resource.close();
} catch (Throwable var11) {
var2.addSuppressed(var11);
}
} else {
resource.close();
}
}
}
} catch (Exception var14) {
var14.printStackTrace();
}
}
}
可以发现编译以后生成了 try-catch-finally 语句块 finally 中的 var2.addSuppressed(var11);
是不是有疑问？其实这么做是为了处理异常屏蔽的，我们将代码修改一下。
资源 Resource.java
/**
资源类
@author hetiantian
*/
public class Resource implements AutoCloseable {
public void sayHello() throws Exception {
throw new Exception("Resource throw Exception");
}
@Override
public void close() throws Exception {
throw new Exception("Close method throw Exception");
}
}
两个方法里面都抛出异常
测试类 CloseResourceIn7.java
/**
jdk7 及以后关闭流的方式
@author hetiantian
*/
public class CloseResourceIn7 {
public static void main(String[] args) {
try {
errorTest();
} catch (Exception e) {
e.printStackTrace();
}
}
private static void errorTest() throws Exception {
Resource resource = null;
try {
resource = new Resource();
resource.sayHello();
}
finally {
if (resource != null) {
resource.close();
}
}
}
}
打印结果：
java.lang.Exception: Close method throw Exception
at com.shuwen.Resource.close(Resource.java:15)
at com.shuwen.CloseResourceIn7.errorTest(CloseResourceIn7.java:27)
at com.shuwen.CloseResourceIn7.main(CloseResourceIn7.java:12)
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