<分区>
我正在测试一些代码来读取类路径中可用的文件，但我最终得到了一些与 Throwable 类的 printStackTrace() 方法相关的有趣的东西。
代码如下:
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.net.URISyntaxException;
import java.net.URL;
import org.apache.commons.io.FileUtils;
import org.apache.commons.io.IOUtils;
public class Main {
public static void main(String[] args) throws IOException, URISyntaxException {
try {
System.out.println("before-test1");
test1(); // will throw exception
System.out.println("after-test1");
} catch (Exception e) {
System.out.println("entering catch-1");
e.printStackTrace();
System.out.println("exiting catch-1");
}
try {
System.out.println("before-test2");
test2();
System.out.println("after-test2");
} catch (Exception e) {
e.printStackTrace();
}
try {
System.out.println("before-test3");
test3();
System.out.println("after-test3");
} catch (Exception e) {
e.printStackTrace();
}
}
private static void test1() throws IOException {
String path = "classpath:/test.txt";
File file = new File(path);
String content = FileUtils.readFileToString(file, "UTF-8");
System.out.println("content = " + content);
}
private static void test2() throws IOException {
String path = "/test.txt";
InputStream in = Main.class.getResourceAsStream(path);
String content = IOUtils.toString(in);
System.out.println("content = " + content);
}
private static void test3() throws IOException, URISyntaxException {
String path = "/test.txt";
URL url = Main.class.getResource(path);
File file = new File(url.toURI());
String content = FileUtils.readFileToString(file, "UTF-8");
System.out.println("content = " + content);
}
}
test.txt的内容只有一行如下:
anil bharadia
现在这个程序的预期输出如下:
before-test1
entering catch-1
java.io.FileNotFoundException: classpath:\test.txt (The filename, directory name, or volume label syntax is incorrect)
at java.io.FileInputStream.open(Native Method)
at java.io.FileInputStream.<init>(Unknown Source)
at org.apache.commons.io.FileUtils.readFileToString(FileUtils.java:874)
at Main.test1(Main.java:50)
at Main.main(Main.java:16)
exiting catch-1
before-test2
content = anil bharadia
after-test2
before-test3
content = anil bharadia
after-test3
当我第一次运行这个类时，我得到了与上面相同的输出。
然后在我再次运行同一个类之后，我得到了以下输出:
before-test1
entering catch-1
exiting catch-1
before-test2
content = anil bharadia
after-test2
before-test3
java.io.FileNotFoundException: classpath:\test.txt (The filename, directory name, or volume label syntax is incorrect)
at java.io.FileInputStream.open(Native Method)
at java.io.FileInputStream.<init>(Unknown Source)
at org.apache.commons.io.FileUtils.readFileToString(FileUtils.java:874)
at Main.test1(Main.java:50)
at Main.main(Main.java:16)
content = anil bharadia
after-test3
在上面的输出中，堆栈跟踪是在调用它的 catch block 执行之后以及 test2() 的执行结束之后打印的。
所以这让我觉得 printStackTrace() 方法在某种程度上是异步的。
我试图查看 printStackTrace() 的源代码，发现以下代码对我没有帮助:
public void printStackTrace(PrintStream s) {
synchronized (s) {
s.println(this);
StackTraceElement[] trace = getOurStackTrace();
for (int i=0; i < trace.length; i++)
s.println("\tat " + trace[i]);
Throwable ourCause = getCause();
if (ourCause != null)
ourCause.printStackTraceAsCause(s, trace);
}
}
我试图用谷歌搜索它，但没有找到任何解释。
当我尝试一次又一次地运行同一个类时，在许多情况下我还发现了以下输出:
java.io.FileNotFoundException: classpath:\test.txt (The filename, directory name, or volume label syntax is incorrect)
at java.io.FileInputStream.open(Native Method)
at java.io.FileInputStream.<init>(Unknown Source)
at org.apache.commons.io.FileUtils.readFileToString(FileUtils.java:874)
at Main.test1(Main.java:50)
at Main.main(Main.java:16)
before-test1
entering catch-1
exiting catch-1
before-test2
content = anil bharadia
after-test2
before-test3
content = anil bharadia
after-test3
这让我想得更多，比如在调用 test1() 方法之前如何打印堆栈跟踪。这是不可能的。