1、jdk7之前的关闭流的操作

/**
 * jdk7以前关闭流的方式
 *
 * @author fcant
 * */
public class CloseResourceBeforeJava7 {
    private static final String FileName = "file.txt";
    public static void main(String[] args) throws IOException {
        FileInputStream inputStream = null;
        try {
            inputStream = new FileInputStream(FileName);
            char c1 = (char) inputStream.read();
            System.out.println("c1=" + c1);
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (inputStream != null) {
                inputStream.close();
            }
        }
    }
}

2、jdk7之后try-with-resource关闭资源

实现了 **java.lang.AutoCloseable**接口（其中，它包括实现了 **java.io.Closeable** 的所有对象），可以使用作为资源。实现java.lang.AutoCloseable接口的Resource类：

/**
 * 资源类
 *
 * @author fcant
 * */
public class Resource implements AutoCloseable {
    public void sayHello() {
        System.out.println("hello");
    }
    @Override
    public void close() throws Exception {
        System.out.println("Resource is closed");
    }
}

/**
 * jdk7及以后关闭流的方式
 *
 * @author fcant
 * */
public class CloseResourceAfterJava7 {
    public static void main(String[] args) {
        try(Resource resource = new Resource()) {
            resource.sayHello();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

输出：

hello
Resource is closed

当存在多个打开资源的时候：

/**
 * 资源2
 *
 * @author fcant
 * */
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");
    }
}

/**
 * jdk7及以后关闭流的方式
 *
 * @author fcant
 * */
public class CloseResourceAfterJava7 {
    public static void main(String[] args) {
        try(Resource resource = new Resource(); Resource2 resource2 = new Resource2()) {
            resource.sayHello();
            resource2.sayhello();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

输出：

hello
Resource say hello
Resource2 is closed
Resource is closed

3、关于异常屏蔽

A.Java7之前-不使用catch抛出异常的写法

将上面的测试类进行修改使用方法抽取异常处理不使用catch抛出异常

/**
 * CloseResourceAfterJava7
 * <p>
 * encoding:UTF-8
 *
 * @author Fcant 下午 22:04 2020/6/26/0026
 */
public class CloseResourceAfterJava7 {
    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();
            }
        }
    }
}

B.Java7之前-使用catch抛出异常的写法

/**
 * CloseResourceAfterJava7
 * <p>
 * encoding:UTF-8
 *
 * @author Fcant 下午 22:04 2020/6/26/0026
 */
public class CloseResourceAfterJava7 {
    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();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (resource != null) {
                resource.close();
            }
        }
    }
}

C.Java7之后-显示被Suppressed屏蔽（未使用catch抛出）[即A中的问题]的异常

①不使用catch处理异常

/**
 * CloseResourceAfterJava7
 * <p>
 * encoding:UTF-8
 *
 * @author Fcant 下午 22:04 2020/6/26/0026
 */
public class CloseResourceAfterJava7 {
    public static void main(String[] args) {
        try {
            errorTest();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    private static void errorTest() throws Exception {
        try (Resource resource = new Resource();) {
            resource.sayHello();
        } 
    }
}

②使用catch处理异常与不使用catch一样

/**
 * CloseResourceAfterJava7
 * <p>
 * encoding:UTF-8
 *
 * @author Fcant 下午 22:04 2020/6/26/0026
 */
public class CloseResourceAfterJava7 {
    public static void main(String[] args) {
        try {
            errorTest();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    private static void errorTest() throws Exception {
        try (Resource resource = new Resource();) {
            resource.sayHello();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

D.分析编译后的class文件查看AutoCloseable怎么处理屏蔽的异常

以下是测试类编译后的class源码文件，并非研究操作的功能源码

public class CloseResourceAfterJava7 {
    public CloseResourceAfterJava7() {
    }
    public static void main(String[] args) {
        try {
            errorTest();
        } catch (Exception var2) {
            var2.printStackTrace();
        }
    }
    private static void errorTest() throws Exception {
        Resource resource = new Resource();
        Throwable var1 = null;
        try {
            resource.sayHello();
        } catch (Throwable var10) {
            var1 = var10;
            throw var10;
        } finally {
            if (resource != null) {
                if (var1 != null) {
                    try {
                        resource.close();
                    } catch (Throwable var9) {
                        var1.addSuppressed(var9);
                    }
                } else {
                    resource.close();
                }
            }
        }
    }
}

可以发现编译以后生成了try-catch-finally语句块 finally中的var1.addSuppressed(var9);
这里可以看到AutoCloseable底层已经转换了try catch，所以我们可以不用catch抛出异常。
另外如果我们写的不够优雅，IDEA也会提示进行转换的

Java 笔记

jdk7以后的异常处理try-with-resource关闭资源