我通常会做以下事情。首先，定义一个基于模板方法的类来处理 try/catch 混乱
import java.io.Closeable;
import java.io.IOException;
import java.util.LinkedList;
import java.util.List;
public abstract class AutoFileCloser {
private static final Closeable NEW_FILE = new Closeable() {
public void close() throws IOException {
// do nothing
}
};
// the core action code that the implementer wants to run
protected abstract void doWork() throws Throwable;
// track a list of closeable thingies to close when finished
private List<Closeable> closeables_ = new LinkedList<Closeable>();
// mark a new file
protected void newFile() {
closeables_.add(0, NEW_FILE);
}
// give the implementer a way to track things to close
// assumes this is called in order for nested closeables,
// inner-most to outer-most
protected void watch(Closeable closeable) {
closeables_.add(0, closeable);
}
public AutoFileCloser() {
// a variable to track a "meaningful" exception, in case
// a close() throws an exception
Throwable pending = null;
try {
doWork(); // do the real work
} catch (Throwable throwable) {
pending = throwable;
} finally {
// close the watched streams
boolean skip = false;
for (Closeable closeable : closeables_) {
if (closeable == NEW_FILE) {
skip = false;
} else if (!skip && closeable != null) {
try {
closeable.close();
// don't try to re-close nested closeables
skip = true;
} catch (Throwable throwable) {
if (pending == null) {
pending = throwable;
}
}
}
}
// if we had a pending exception, rethrow it
// this is necessary b/c the close can throw an
// exception, which would remove the pending
// status of any exception thrown in the try block
if (pending != null) {
if (pending instanceof RuntimeException) {
throw (RuntimeException) pending;
} else {
throw new RuntimeException(pending);
}
}
}
}
}
注意“待处理”异常——这会处理关闭期间抛出的异常会掩盖我们可能真正关心的异常的情况。
finally 会首先尝试从任何装饰流的外部关闭，因此如果您有一个包装 FileWriter 的 BufferedWriter，我们会尝试先关闭 BuffereredWriter，如果失败，仍然尝试关闭 FileWriter 本身。
上面的类可以这样使用：
try {
// ...
new AutoFileCloser() {
@Override protected void doWork() throws Throwable {
// declare variables for the readers and "watch" them
FileReader fileReader = null;
BufferedReader bufferedReader = null;
watch(fileReader = new FileReader("somefile"));
watch(bufferedReader = new BufferedReader(fileReader));
// ... do something with bufferedReader
// if you need more than one reader or writer
newFile(); // puts a flag in the
FileWriter fileWriter = null;
BufferedWriter bufferedWriter = null;
watch(fileWriter = new FileWriter("someOtherFile"));
watch(bufferedWriter = new BufferedWriter(fileWriter));
// ... do something with bufferedWriter
}
};
// .. other logic, maybe more AutoFileClosers
} catch (RuntimeException e) {
// report or log the exception
}
使用这种方法，您永远不必担心 try/catch/finally 会再次处理关闭文件。
如果这对你来说太重了，至少考虑一下 try/catch 和它使用的“挂起”变量方法。