我是一个长期的读者，但第一次写作。
我目前正在尝试在我们的代码库中使用 AspectJ 实现一个记录器。 AspectJ 似乎运行良好，但我遇到了非常奇怪的 Java 错误。我是一名长期的 C++ 和 .Net 开发人员，仍在适应 Java 的世界，所以如果这是一个愚蠢的问题，我深表歉意。
我的代码试图捕获异常，并将相关信息记录到文本文件中。陷阱工作正常，但我注意到在部署时我没有获得任何数据。我在 Java 反编译器中打开了我的类文件，并注意到 PrintWriter 似乎正在生成错误。我从来没有见过这样的问题，所以我希望你能有任何见解。
package mil.uscg.c3cen.vic.aspect;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.AfterThrowing;
import org.aspectj.lang.JoinPoint;
@Aspect
public class LoggingAspect
{
private final String LOG_FILE = "aspectLog.txt";
private final File file = new File(LOG_FILE);
private LoggingAspect()
{
}
private void logException(String msg)
{
try
{
if(!file.exists())
file.createNewFile();
}
catch(IOException e)
{
}
try (FileWriter fw = new FileWriter(file);
BufferedWriter bw = new BufferedWriter(fw);
PrintWriter pw = new PrintWriter(bw))
{
pw.println(msg);
}
catch(IOException e)
{
}
}
private String getSimpleFunctionInfo(String className, String function, Object[] args)
{
StringBuilder builder = new StringBuilder();
builder.append(". Method: ");
builder.append(className);
builder.append(".");
builder.append(function);
if(args.length == 0)
{
builder.append("()");
return builder.toString();
}
builder.append("(");
for(Object o : args)
{
builder.append(o.toString());
builder.append(",");
}
// Replace the comma for the last param with a closing parenthesis
int len = builder.length();
builder.replace(len -1, len, ")");
return builder.toString();
}
// Returns a formatted exception. "Exception.ErrorMessage"
private String getSimpleExceptionInfo(String name, String msg)
{
StringBuilder builder = new StringBuilder();
builder.append("Exception caught: ");
builder.append(name);
builder.append(". Message: ");
builder.append(msg);
return builder.toString();
}
@AfterThrowing(pointcut = "execution(* mil.uscg.c3cen.*.*.*(..)) "
//+ "&& !within(mil.uscg.c3cen.vic.aspect.*) "
, throwing = "excep")
public void afterThrowing(JoinPoint jp, Throwable excep) throws Throwable
{
String ex = getSimpleExceptionInfo(excep.getClass().getSimpleName(),
excep.getMessage());
String name = getSimpleFunctionInfo(jp.getSignature().getDeclaringType().getSimpleName(),
jp.getSignature().getName(),
jp.getArgs());
StringBuilder builder = new StringBuilder();
builder.append(ex);
builder.append(name);
logException(builder.toString());
}
}
除函数 logException 外，类文件中的一切看起来都与您预期的一样。
/* Error */
private void logException(String msg)
{
// Byte code:
// 0: aload_0
// 1: getfield 25 mil/uscg/c3cen/vic/aspect/LoggingAspect:file Ljava/io/File;
// 4: invokevirtual 32 java/io/File:exists ()Z
// 7: ifne +15 -> 22
// 10: aload_0
// 11: getfield 25 mil/uscg/c3cen/vic/aspect/LoggingAspect:file Ljava/io/File;
// 14: invokevirtual 36 java/io/File:createNewFile ()Z
// 17: pop
// 18: goto +4 -> 22
// 21: pop
// 22: aconst_null
// 23: astore_2
// 24: aconst_null
// 25: astore_3
// 26: new 39 java/io/FileWriter
// 29: dup
// 30: aload_0
// 31: getfield 25 mil/uscg/c3cen/vic/aspect/LoggingAspect:file Ljava/io/File;
// 34: invokespecial 41 java/io/FileWriter:<init> (Ljava/io/File;)V
// 37: astore 4
// 39: new 44 java/io/BufferedWriter
// 42: dup
// 43: aload 4
// 45: invokespecial 46 java/io/BufferedWriter:<init> (Ljava/io/Writer;)V
// 48: astore 5
// 50: new 49 java/io/PrintWriter
// 53: dup
// 54: aload 5
// 56: invokespecial 51 java/io/PrintWriter:<init> (Ljava/io/Writer;)V
// 59: astore 6
// 61: aload 6
// 63: aload_1
// 64: invokevirtual 52 java/io/PrintWriter:println (Ljava/lang/String;)V
// 67: aload 6
// 69: ifnull +24 -> 93
// 72: aload 6
// 74: invokevirtual 55 java/io/PrintWriter:close ()V
// 77: goto +16 -> 93
// 80: astore_2
// 81: aload 6
// 83: ifnull +8 -> 91
// 86: aload 6
// 88: invokevirtual 55 java/io/PrintWriter:close ()V
// 91: aload_2
// 92: athrow
// 93: aload 5
// 95: ifnull +43 -> 138
// 98: aload 5
// 100: invokevirtual 58 java/io/BufferedWriter:close ()V
// 103: goto +35 -> 138
// 106: astore_3
// 107: aload_2
// 108: ifnonnull +8 -> 116
// 111: aload_3
// 112: astore_2
// 113: goto +13 -> 126
// 116: aload_2
// 117: aload_3
// 118: if_acmpeq +8 -> 126
// 121: aload_2
// 122: aload_3
// 123: invokevirtual 59 java/lang/Throwable:addSuppressed (Ljava/lang/Throwable;)V
// 126: aload 5
// 128: ifnull +8 -> 136
// 131: aload 5
// 133: invokevirtual 58 java/io/BufferedWriter:close ()V
// 136: aload_2
// 137: athrow
// 138: aload 4
// 140: ifnull +66 -> 206
// 143: aload 4
// 145: invokevirtual 65 java/io/FileWriter:close ()V
// 148: goto +58 -> 206
// 151: astore_3
// 152: aload_2
// 153: ifnonnull +8 -> 161
// 156: aload_3
// 157: astore_2
// 158: goto +13 -> 171
// 161: aload_2
// 162: aload_3
// 163: if_acmpeq +8 -> 171
// 166: aload_2
// 167: aload_3
// 168: invokevirtual 59 java/lang/Throwable:addSuppressed (Ljava/lang/Throwable;)V
// 171: aload 4
// 173: ifnull +8 -> 181
// 176: aload 4
// 178: invokevirtual 65 java/io/FileWriter:close ()V
// 181: aload_2
// 182: athrow
// 183: astore_3
// 184: aload_2
// 185: ifnonnull +8 -> 193
// 188: aload_3
// 189: astore_2
// 190: goto +13 -> 203
// 193: aload_2
// 194: aload_3
// 195: if_acmpeq +8 -> 203
// 198: aload_2
// 199: aload_3
// 200: invokevirtual 59 java/lang/Throwable:addSuppressed (Ljava/lang/Throwable;)V
// 203: aload_2
// 204: athrow
// 205: pop
// 206: return
// Line number table:
// Java source line #28 -> byte code offset #0
// Java source line #29 -> byte code offset #10
// Java source line #30 -> byte code offset #18
// Java source line #31 -> byte code offset #21
// Java source line #36 -> byte code offset #22
// Java source line #36 -> byte code offset #26
// Java source line #37 -> byte code offset #39
// Java source line #38 -> byte code offset #50
// Java source line #40 -> byte code offset #61
// Java source line #41 -> byte code offset #67
// Java source line #42 -> byte code offset #205
// Java source line #46 -> byte code offset #206
// Local variable table:
// start length slot name signature
// 0 207 0 this LoggingAspect
// 0 207 1 msg String
// 23 1 2 localObject1 Object
// 80 28 2 localObject2 Object
// 112 92 2 localObject3 Object
// 25 1 3 localObject4 Object
// 106 17 3 localThrowable1 Throwable
// 151 17 3 localThrowable2 Throwable
// 183 17 3 localThrowable3 Throwable
// 37 140 4 fw java.io.FileWriter
// 48 84 5 bw java.io.BufferedWriter
// 59 28 6 pw java.io.PrintWriter
// 21 1 12 localIOException1 java.io.IOException
// 205 1 13 localIOException2 java.io.IOException
// Exception table:
// from to target type
// 0 18 21 java/io/IOException
// 61 67 80 finally
// 50 93 106 finally
// 39 138 151 finally
// 26 183 183 finally
// 22 205 205 java/io/IOException
}
这真的让我很困惑，所以任何信息都将不胜感激。谢谢!
最佳答案
好的，我尝试使用 Java 8 和当前的 AspectJ 1.8.8。您的方面按预期工作(我编译它时没有任何更改)。它只是有点过于复杂，应该简化。此外，您可能只是错误地计算了切入点中 .* 的数量。
如果我在你的建议方法的开头添加 System.out.println(jp); 以便在控制台上看到一些东西并针对这个示例驱动程序类运行你的方面...
package mil.uscg.c3cen.foo;
public class Application {
public static void main(String[] args) {
for (int i = 0; i < 3; i++) {
try {
doSomething();
}
catch (Exception e) {}
}
}
public static void doSomething() {
System.out.println("Calculation result = " + multiply(add(3, 4), 5));
System.out.println("Calculation result = " + divide(add(5, 6), 0));
}
private static int add(int summand1, int summand2) {
return summand1 + summand2;
}
private static int multiply(int factor1, int factor2) {
return factor1 * factor2;
}
private static int divide(int dividend, int divisor) {
return dividend / divisor;
}
}
...控制台日志如下所示:
Calculation result = 35
execution(int mil.uscg.c3cen.foo.Application.divide(int, int))
execution(void mil.uscg.c3cen.foo.Application.doSomething())
Calculation result = 35
execution(int mil.uscg.c3cen.foo.Application.divide(int, int))
execution(void mil.uscg.c3cen.foo.Application.doSomething())
Calculation result = 35
execution(int mil.uscg.c3cen.foo.Application.divide(int, int))
execution(void mil.uscg.c3cen.foo.Application.doSomething())
如您所见，只有在调用层次结构中向上抛出异常(直到它们被捕获)的方法才会被记录，正如预期的那样。日志文件 aspectLog.txt 包含以下内容:
Exception caught: ArithmeticException. Message: / by zero. Method: Application.main([Ljava.lang.String;@f6f4d33)
需要改进的地方:
- 也许你想要一个更稳定的切入点，以
mil.uscg.c3cen的所有子包为目标。 “该包及其所有子包中的所有方法执行”的语法为execution(* mil.uscg.c3cen..*(..))。 - 您的日志文件使用逻辑中存在一个错误:每当发生第一个异常并且日志文件尚不存在时，它就会被记录下来并立即关闭日志文件。永远不会记录任何后续异常，这可能不是您想要的。只要 JVM 启动并运行，您可能希望将多个异常记录到同一个文件中。因此，您不想在每次写入后关闭日志文件，而是在 JVM 生命周期结束时在 JVM 关闭 Hook 中处理它。 Try with (auto-closeable) resources 只有在你真的想在运行代码的某一部分后关闭它们时才有用。顺便说一句，您可以通过定期刷新编写器来避免关闭 Hook ，例如在每次
println调用之后。 - 我在这里不讨论线程和同步问题，那需要更加小心。让我们假设您有一个单线程应用程序。
- 也许您还想拦截构造函数中的异常并将其添加到您的切入点。
改进和简化方面:
package mil.uscg.c3cen.vic.aspect;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.PrintWriter;
import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.annotation.AfterThrowing;
import org.aspectj.lang.annotation.Aspect;
@Aspect
public class LoggingAspect {
private static final String LOG_FILE = "aspectLog.txt";
private final PrintWriter logWriter;
public LoggingAspect() throws FileNotFoundException {
logWriter = new PrintWriter(new FileOutputStream(LOG_FILE));
Runtime.getRuntime().addShutdownHook(new Thread() {
@Override
public void run() {
logWriter.close();
}
});
}
@AfterThrowing(
pointcut =
"(execution(* mil.uscg.c3cen..*(..)) || execution(mil.uscg.c3cen..new(..)))" +
" && !within(mil.uscg.c3cen.vic.aspect..*) ",
throwing = "excep"
)
public void afterThrowing(JoinPoint jp, Throwable excep) throws Throwable {
//System.out.println(excep + " -> " + jp);
logWriter.println(excep + " -> " + jp);
}
}
带有构造函数抛出异常的扩展代码示例:
package mil.uscg.c3cen.foo;
public class Application {
public Application() {
System.out.println(1/0);
}
public static void doSomething() {
System.out.println("Calculation result = " + multiply(add(3, 4), 5));
System.out.println("Calculation result = " + divide(add(5, 6), 0));
}
private static int add(int summand1, int summand2) {
return summand1 + summand2;
}
private static int multiply(int factor1, int factor2) {
return factor1 * factor2;
}
private static int divide(int dividend, int divisor) {
return dividend / divisor;
}
public static void main(String[] args) {
for (int i = 0; i < 3; i++) {
try {
doSomething();
}
catch (Exception e) {}
}
try {
new Application();
}
catch (Exception e) {}
}
}
控制台日志:
Calculation result = 35
Calculation result = 35
Calculation result = 35
日志文件:
java.lang.ArithmeticException: / by zero -> execution(int mil.uscg.c3cen.foo.Application.divide(int, int))
java.lang.ArithmeticException: / by zero -> execution(void mil.uscg.c3cen.foo.Application.doSomething())
java.lang.ArithmeticException: / by zero -> execution(int mil.uscg.c3cen.foo.Application.divide(int, int))
java.lang.ArithmeticException: / by zero -> execution(void mil.uscg.c3cen.foo.Application.doSomething())
java.lang.ArithmeticException: / by zero -> execution(int mil.uscg.c3cen.foo.Application.divide(int, int))
java.lang.ArithmeticException: / by zero -> execution(void mil.uscg.c3cen.foo.Application.doSomething())
java.lang.ArithmeticException: / by zero -> execution(mil.uscg.c3cen.foo.Application())
查看最后一行，您会在构造函数中看到异常。
如果您想稍微美化异常日志输出，类似于您原来的方面所做的，请执行以下操作:
logWriter.println(excep.getClass().getSimpleName() + " -> " + jp.getSignature());
然后日志文件变成:
ArithmeticException -> int mil.uscg.c3cen.foo.Application.divide(int, int)
ArithmeticException -> void mil.uscg.c3cen.foo.Application.doSomething()
ArithmeticException -> int mil.uscg.c3cen.foo.Application.divide(int, int)
ArithmeticException -> void mil.uscg.c3cen.foo.Application.doSomething()
ArithmeticException -> int mil.uscg.c3cen.foo.Application.divide(int, int)
ArithmeticException -> void mil.uscg.c3cen.foo.Application.doSomething()
ArithmeticException -> mil.uscg.c3cen.foo.Application()
关于Java PrintWriter 错误，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/35581814/