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法律学如何在Java中从控制台获取异常日志并将其写入外部文件？
有几种日志框架可用于将数据记录到文件中。您也可以定义自己的方法。
示例 - 使用 I/O 包
下面的 Java 程序有一个存储 5 个整数值的数组，我们允许用户从数组中选择两个元素（元素的索引）并在它们之间执行除法运算。我们将此代码包装在 try 块中，并使用三个 catch 块捕获 ArithmeticException、InputMismatchException 和 ArrayIndexOutOfBoundsException。在每个块中，我们都调用 writeToFile() 方法。
此方法接受一个异常对象，并使用 Files 类的 write() 方法将其追加到文件中。
示例
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;
import java.time.LocalDateTime;
import java.util.Arrays;
import java.util.InputMismatchException;
import java.util.Scanner;
public class LoggingToFile {
private static void writeToFile(Exception ex) throws IOException {
//Retrieving the log file
Path logFile = Paths.get("ExceptionLog.txt");
//Preparing the data to be logged
byte bytes[] = ("\r
"+LocalDateTime.now()+": "+ ex.toString()).getBytes();
//Appending the exception to your file
Files.write(logFile, bytes, StandardOpenOption.APPEND);
System.out.println("Exception logged to your file");
}
public static void main(String [] args) throws IOException {
Scanner sc = new Scanner(System.in);
int[] arr = {10, 20, 30, 2, 0, 8};
System.out.println("Array: "+Arrays.toString(arr));
System.out.println("Choose numerator and denominator (not 0) from this array (enter positions 0 to 5)");
try {
int a = sc.nextInt();
int b = sc.nextInt();
int result = (arr[a])/(arr[b]);
System.out.println("Result of "+arr[a]+"/"+arr[b]+": "+result);
}catch(ArrayIndexOutOfBoundsException ex) {
System.out.println("Warning: You have chosen a position which is not in the array");
writeToFile(ex);
}catch(ArithmeticException ex) {
System.out.println("Warning: You cannot divide an number with 0");
writeToFile(ex);
}catch(InputMismatchException ex) {
System.out.println("Warning: You have entered invalid input");
writeToFile(ex);
}
}
}输出1
Enter 3 integer values one by one: Array: [10, 20, 30, 2, 0, 8] Choose numerator and denominator(not 0) from this array (enter positions 0 to 5) 2 4 Warning: You cannot divide an number with 0 Exception logged to your file
输出2
Enter 3 integer values one by one: Array: [10, 20, 30, 2, 0, 8] Choose numerator and denominator(not 0) from this array (enter positions 0 to 5) 5 12 Warning: You have chosen a position which is not in the array Exception logged to your file
输出3
Enter 3 integer values one by one: Array: [10, 20, 30, 2, 0, 8] Choose numerator and denominator(not 0) from this array (enter positions 0 to 5) hello Warning: You have entered invalid input Exception logged to your file
ExceptionLog.txt
2019-07-19T17:57:09.735: java.lang.ArithmeticException: / by zero 2019-07-19T17:57:39.025: java.lang.ArrayIndexOutOfBoundsException: 12 2019-07-19T18:00:23.374: java.util.InputMismatchException
使用 log4j 将异常记录到文件
以下示例使用日志库 log4j 将异常记录到文件中。
Log4j2.xml
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="Example" packages="">
<Appenders>
<File name="file" fileName="d:/example.log">
<PatternLayout>
<Pattern>%d %p %c{1.} [%t] %m%n</Pattern>
</PatternLayout>
</File>
</Appenders>
<Loggers>
<Root level="info">
<AppenderRef ref="file"/>
</Root>
</Loggers>
</ConfigurationPom.xml
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 ">http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>com.javacodegeeks.snippets.enterprise</groupId> <artifactId>log4jexample</artifactId> <version>0.0.1-SNAPSHOT</version> <dependencies> <dependency> <groupId>org.apache.logging.log4j</groupId> <artifactId>log4j-api</artifactId> <version>2.12.0</version> </dependency> <dependency> <groupId>org.apache.logging.log4j</groupId> <artifactId>log4j-core</artifactId> <version>2.12.0</version> </dependency> </dependencies> </project>
LoggingToFile.java
下面的 Java 程序有一个存储 5 个整数值的数组，我们允许用户从数组中选择两个元素（元素的索引）并在它们之间执行除法运算。我们将此代码包装在 try 块中，并使用三个 catch 块捕获 ArithmeticException、InputMismatchException 和 ArrayIndexOutOfBoundsException。在每个块中，我们都调用 writeToFile() 方法。
此方法接受一个异常对象，并使用 Files 类的 write() 方法将其追加到文件中。
示例
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;
import java.time.LocalDateTime;
import java.util.Arrays;
import java.util.InputMismatchException;
import java.util.Scanner;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
public class LoggingToFile {
static Logger log = LogManager.getLogger(Sample.class.getName());
private static void writeToFile(Exception ex) throws IOException {
//Retrieving the log file
Path logFile = Paths.get("ExceptionLog.txt");
//Preparing the data to be logged
byte bytes[] = ("\r
"+LocalDateTime.now()+": "+ ex.toString()).getBytes();
//Appending the exception to your file
Files.write(logFile, bytes, StandardOpenOption.APPEND);
System.out.println("Exception logged to your file");
}
public static void main(String [] args) throws IOException {
Scanner sc = new Scanner(System.in);
int[] arr = {10, 20, 30, 2, 0, 8};
System.out.println("Array: "+Arrays.toString(arr));
System.out.println("Choose numerator and denominator (not 0) from this array (enter positions 0 to 5)");
try {
int a = sc.nextInt();
int b = sc.nextInt();
int result = (arr[a])/(arr[b]);
System.out.println("Result of "+arr[a]+"/"+arr[b]+": "+result);
}catch(ArrayIndexOutOfBoundsException ex) {
System.out.println("Warning: You have chosen a position which is not in the array");
log.info(ex.toString());
System.out.println("Exception logged to your file");
}catch(ArithmeticException ex) {
System.out.println("Warning: You cannot divide an number with 0");
log.info(ex.toString());
System.out.println("Exception logged to your file");
}catch(InputMismatchException ex) {
System.out.println("Warning: You have entered invalid input");
log.info(ex.toString());
System.out.println("Exception logged to your file");
}
}
}输出1
Array: [10, 20, 30, 2, 0, 8] Choose numerator and denominator(not 0) from this array (enter positions 0 to 5) 2 4 Warning: You cannot divide an number with 0 Exception logged to your file
输出2
Array: [10, 20, 30, 2, 0, 8] Choose numerator and denominator(not 0) from this array (enter positions 0 to 5) 5 12 Warning: You have chosen a position which is not in the array Exception logged to your file
输出3
Array: [10, 20, 30, 2, 0, 8] Choose numerator and denominator(not 0) from this array (enter positions 0 to 5) hi Warning: You have entered invalid input Exception logged to your file
ExceptionLog.txt
2019-08-01 13:53:13,943 INFO a.Sample [main] java.lang.ArithmeticException: / by zero 2019-08-01 13:53:45,127 INFO a.Sample [main] java.lang.ArrayIndexOutOfBoundsException: 12 2019-08-01 13:54:06,500 INFO a.Sample [main] java.util.InputMismatchException
更新于：2019年9月12日
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