android.os.Debug

发现代码之美

日志

05-08 17:01:07.156   997   997 W ContextImpl: Calling a method in the system process without a qualified user: android.app.ContextImpl.sendBroadcast:877 android.content.ContextWrapper.sendBroadcast:421 com.galanz.ovena6.ui.setting.FactoryResetConfirmActivity$cleanData$1$2.invokeSuspend:94 kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith:33 kotlinx.coroutines.DispatchedTask.run:241 

追问

它是怎么实现这行日志的打印？

代码跟踪

1.android.app.ContextImpl.sendBroadcast
    public void sendBroadcast(Intent intent) {
        warnIfCallingFromSystemProcess();
        ····
    }

2.android.app.ContextImpl.warnIfCallingFromSystemProcess
    private void warnIfCallingFromSystemProcess() {
        if (Process.myUid() == Process.SYSTEM_UID) {
            Slog.w(TAG, "Calling a method in the system process without a qualified user: "
                    + Debug.getCallers(5));
        }
    }
    
3.android.os.Debug.getCallers
    /**
     * Return a string consisting of methods and locations at multiple call stack levels.
     * @param depth the number of levels to return, starting with the immediate caller.
     * @return a string describing the call stack.
     * {@hide}  //注意这个方法是hide
     */
    public static String getCallers(final int depth) {
        final StackTraceElement[] callStack = Thread.currentThread().getStackTrace();//高级货
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < depth; i++) {
            sb.append(getCaller(callStack, i)).append(" ");
        }
        return sb.toString();
    }
    
    private static String getCaller(StackTraceElement callStack[], int depth) {
        // callStack[4] is the caller of the method that called getCallers()
        if (4 + depth >= callStack.length) {
            return "";
        }
        StackTraceElement caller = callStack[4 + depth];//从StackTraceElement中获取各种变量
        return caller.getClassName() + "." + caller.getMethodName() + ":" + caller.getLineNumber();//输出特定的日志格式
    }

关键分析

1.通过当前线程(Thread.currentThread())中获取栈信息
StackTraceElement[] callStack = Thread.currentThread().getStackTrace();

2.每个StackTraceElement对象包含各种变量：
class StackTraceElement implements java.io.Serializable 

    private String declaringClass;
    private String methodName;
    private String fileName;
    private int    lineNumber;

拓展

通过此方法是不是能达到打断点看业务代码流程的效果？