假设我在一个非常大的项目中工作，并且注意到一个空打印行，所以我假设有一个 System.out.println("");位于代码中的某处。除了在整个项目中搜索所有出现的 System.out.println 之外，我将如何尝试找出它在哪里？
【问题讨论】：
标签： java reflection
您可以实现自己的PrintStream 并使用System.setOut 替换默认的标准输出。然后要么在类里面放一个调试标记（如果打印的是空字符串），要么通过调用栈打印出方法名（抛出并捕获异常并获取栈信息）。
【讨论】：
如果您使用的是 Java 8+，Durian 有一个 StackDumper 类，可以轻松找到给定行的打印位置：
StackDumper.dumpWhenSysOutContains("SomeTrigger")
当打印“SomeTrigger”时，这将被转储到System.err：
+----------\
| Triggered by SomeTrigger
| at package.MyClass.myMethod(MyClass.java:62)
| (the rest of the stacktrace)
+----------/
对于你的情况（寻找一个空字符串），它有点复杂：
PrintStream sysOutClean = System.out;
StringPrinter sysOutReplacement = new StringPrinter(StringPrinter.stringsToLines(line -> {
if (line.isEmpty()) {
StackDumper.dump("Found empty line");
}
sysOutClean.println(line);
}));
System.setOut(sysOutReplacement.toPrintStream());
现在如果有这样的事情：
System.out.println("ABC");
System.out.println("123");
System.out.println("");
System.out.println("DEF");
然后您的控制台将如下所示：
ABC
123
+----------\
| Found empty line
| at package.MyClass.myMethod(MyClass.java:62)
| (the rest of the stacktrace)
+----------/
DEF
【讨论】：
例子：
/** Control sysout prints */
public static void main(String[] arg) throws Exception {
System.out.println("Default"); //print normally
SysOutController.setSysOutLocationAddressor();
System.out.println("With Address"); //prints with calling location, and on click location cursor directly focus when System.out.**() called
SysOutController.ignoreSysout();
System.out.println("Ignored"); //this line will never prints
SysOutController.resetSysOut();
System.out.println("Default"); //print normally as it is (reset)
}
只需调用下面类的方法，方便开发者控制sysout
import java.io.FileDescriptor;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.io.PrintStream;
/**
* Class which controls System.out prints in console <br/>
* this class will helps developers to control prints in console
* @implSpec
* <pre><code>
* System.out.println("Default"); //print normally
*
* SysOutController.setSysOutLocationAddressor();
* System.out.println("With Address"); //prints with calling location
*
* SysOutController.ignoreSysout();
* System.out.println("Ignored"); //this line will never prints
*
* SysOutController.resetSysOut();
* System.out.println("Default"); //print normally as it is (reset)
* </code></pre>
* @author Dharmendrasinh Chudasama
*/
public class SysOutController {
private static void setOut(OutputStream out){
System.setOut(new PrintStream(out));
}
private static final OutputStream CONSOLE = new FileOutputStream(FileDescriptor.out);
/**
* Reset System.out.print* method
* @author Dharmendrasinh Chudasama
*/
public static void resetSysOut() { setOut(CONSOLE); }
/**
* System.out.print* will not print anything in console
* @author Dharmendrasinh Chudasama
*/
public static void ignoreSysout() {
setOut(new OutputStream() {
@Override public void write(int b) throws IOException {}
});
}
/**
* Address/location of calling System.out.* method will append in console
* @author Dharmendrasinh Chudasama
*/
public static void setSysOutLocationAddressor() {
setOut(new OutputStream() {
@Override
public void write(int b) throws IOException {
if(b=='\n'){ //if newLine
final StackTraceElement callerStEl = new Throwable().getStackTrace()[9];
String pathData =
"\u001B[37m" //low-visibality
+ "\t :: ("+callerStEl.getFileName()+":"+callerStEl.getLineNumber()+") ["+callerStEl+"]" //code path
+ "\u001B[0m "; //reset
CONSOLE.write(pathData.getBytes());
}
CONSOLE.write(b);
}
});
}
}
【讨论】：
这也可能是某些库的原因，如果您觉得只是 System.out.println 的原因，那么，
解决方案 1： 下面的代码 sn-p 应该可以帮助您找出执行它的位置。
import java.io.FileNotFoundException;
import java.io.PrintStream;
public class CustomPrintStream extends PrintStream {
public CustomPrintStream(String fileName) throws FileNotFoundException {
super(fileName);
}
@Override
public void print(String s) {
try{
if(s == null || s.equals("")){
throw new Exception("Invalid print message");
}
super.print(s);
}catch(Exception e){
//TODO Change to your logger framework and leave it as same
e.printStackTrace();
}
}
public static void main(String[] args) {
try {
//TODO : Change to your favorite path and make sure mentioned
//file is available
CustomPrintStream customPrintStream = new CustomPrintStream
("/home/prem/Desktop/test.log");
System.setOut(customPrintStream);
System.out.println("");
} catch (FileNotFoundException e) {
//TODO Change to your logger framework and leave it as same
e.printStackTrace();
}
}
}
解决方案 2： 由于 IDE 可用，请从他们那里获得帮助。如果您使用的是 eclipse 菜单 -> 搜索 -> 文件搜索-> 放置 System.out.println("");在包含搜索和搜索它。
我宁愿不要在任何代码中使用 System.out.println，您可以使用 checkstyle 并确信从此没有开发人员使用它们。
【讨论】：
定义一个类 NewPrintStream 扩展 PrintStream
import java.io.FileNotFoundException;
import java.io.PrintStream;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class NewPrintStream extends PrintStream {
private static final Logger LOGGER = LoggerFactory.getLogger(NewPrintStream.class);
public NewPrintStream(String fileName) throws FileNotFoundException {
super(fileName);
}
@Override
public void println(String x) {
LOGGER.info("xxxxxxx", new Exception("xxxx"));
}
}
然后在主类中设置stdout/stderr打印流
System.setOut(new NewPrintStream("aaa"));
System.setErr(new NewPrintStream("aaa"));
【讨论】：
在PrintStream.println(String x) 中放置一个条件断点，条件设置为x.equals("") 或任何您的字符串。
【讨论】：