System.out 临时重定向后的奇怪控制台输出

Question

正常情况下代码如下：

String[] outputStrings =  {" Initial values: a = 1, b = 2 ", "Swapped values: a = 2, b = 1", ""};

System.out.println("array length: " + outputStrings.length);

int i = 0;
for (String line: outputStrings) {
    String str = Integer.toString(i) + " : |" + line + "| ";
    System.out.println(str);
    //System.out.flush();
    i++;
}

有以下输出：

array length: 3
0 : | Initial values: a = 1, b = 2 | 
1 : |Swapped values: a = 2, b = 1| 
2 : ||

但是，下面的代码：

CommandLineTestScaffolding scaffolding;
scaffolding = new CommandLineTestScaffolding(ExchangeCL::main);

String[] inputStrings = {"1", "2"}; // string literals with integer numbers
String[] outputStrings = scaffolding.run(inputStrings);

scaffolding = null; //no longer necessary

System.out.println("array length: " + outputStrings.length);

int i = 0;
for (String line: outputStrings) {
    String str = Integer.toString(i) + " : |" + line + "| ";
    System.out.println(str);
    //System.out.flush();
    i++;
}

有以下奇怪的输出：

array length: 1
0 : | Initial values: a = 1, b = 2 
Swapped values: a = 2, b = 1
| 

有关信息，CommandLineTestScaffolding 是临时重定向 System.out 以获取命令行输出到字符串数组的简单装置：

public class CommandLineTestScaffolding {

    private Consumer<String[]> theMethod; //Place to store main method generating text output

    public CommandLineTestScaffolding(Consumer<String[]> method) {

        theMethod = method;
    }

    public String[] run(String[] args) {

        // Create a stream to hold the output
        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
        PrintStream printStream = new PrintStream(outputStream);

        // A variable to temporarily hold System.out stream
        PrintStream oldOutputStream = null;

        // Critical section. System.out must be restored to its original value
        try {

            System.out.flush(); // Clear buffer;

            // IMPORTANT: Save the old System.out!
            oldOutputStream = System.out;

            // Use new wrapped byte array stream
            System.setOut(printStream);

            theMethod.accept(args); //Run the method. fill the stream

            printStream.flush(); // Clear buffer;

        }
        finally {

            // Put things back
            System.setOut(oldOutputStream);

        }

        String[] output = outputStream.toString().split("/n"); //split into lines with regex
        printStream = null;
        outputStream = null;
        return output;
    }

}

是什么导致了这种奇怪的行为？

Answer 1

outputStrings 只有一个元素，它是 "0 : | 初始值：a = 1, b = 2 交换值：a = 2，b = 1 | "

所以，这不是奇怪的行为。

您的 CommandLineTestScaffolding 无法完成您期望的工作。

但是，我不明白您需要什么？您需要与 1 完全相同的输出吗？