### 異常屏蔽 直接上代碼： ``` public class Connection implements AutoCloseable { public void sendData() throws Exception { throw new Exception("send data"); } @Override public void close() throws Exception { throw new MyException("close"); } } public class TryWithResource { public static void main(String[] args) { try { test(); } catch (Exception e) { e.printStackTrace(); } } private static void test() throws Exception { Connection conn = null; try { conn = new Connection(); conn.sendData(); } finally { if (conn != null) { conn.close(); } } } } output==> basic.exception.MyException: close at basic.exception.Connection.close(Connection.java:10) at basic.exception.TryWithResource.test(TryWithResource.java:82) at basic.exception.TryWithResource.main(TryWithResource.java:7) ...... ``` 由于我們一次只能拋出一個異常，所以在最上層看到的是最后一個拋出的異常——也就是close方法拋出的MyException，而sendData拋出的Exception被忽略了。這就是所謂的異常屏蔽。由于異常信息的丟失，異常屏蔽可能會導致某些bug變得極其難以發現，程序員們不得不加班加點地找bug，如此毒瘤，怎能不除！幸好，為了解決這個問題，從Java 1.7開始，大佬們為Throwable類新增了addSuppressed方法，支持將一個異常附加到另一個異常身上，從而避免異常屏蔽。那么被屏蔽的異常信息會通過怎樣的格式輸出呢？我們再運行一遍剛才用try-with-resource包裹的main方法： ``` public class TryWithResource { public static void main(String[] args) { try (Connection conn = new Connection()) { conn.sendData(); } catch (Exception e) { e.printStackTrace(); } } } output==> java.lang.Exception: send data at basic.exception.Connection.sendData(Connection.java:5) at basic.exception.TryWithResource.main(TryWithResource.java:14) ...... Suppressed: basic.exception.MyException: close at basic.exception.Connection.close(Connection.java:10) at basic.exception.TryWithResource.main(TryWithResource.java:15) ... 5 more ``` 具體原因是編譯器幫我們將一個異常附加到了另一個異常上\(var2.addSuppressed\(var11\)\)： ``` public class AppTest { public AppTest() { } public static void main(String[] args) { try { AppTest.Connection con = new AppTest.Connection(); Throwable var2 = null; try { con.print(); } catch (Throwable var12) { var2 = var12; throw var12; } finally { if (con != null) { if (var2 != null) { try { con.close(); } catch (Throwable var11) { var2.addSuppressed(var11); } } else { con.close(); } } } } catch (Exception var14) { var14.printStackTrace(); } } static class Connection implements AutoCloseable { Connection() { } public void print() { System.err.println("print data==>"); } public void close() throws Exception { System.err.println("auto close===>"); } } } ```