Trino 源码剖析

Functions

function 反射和注册

io.trino.operator.scalar.annotations.ScalarFromAnnotationsParser

这里是提取注解元素的方法
String baseName = scalarFunction.value().isEmpty() ? camelToSnake(annotatedName(annotated)) : scalarFunction.value();

这里如果 scalarFunction 的注解没有没有值，直接对函数名进行snake命名法

一般程序设计中，有两种变量命名规范：Snake方式和Camel方式。

• Snake方式是指单词用小写字母，单词间下划线（“_”）代替空格；
• Camel方式是指相邻单词首字母用大写表示，对单词加以区分。

例如，你想定义一个变量表示一个数组数字之和，并且用英文“sum of array”。我们使用Snake方式的变量名为：sum_of_array；用Camel命名方式的变量名为：sumOfArray。

  public static List<ScalarImplementationHeader> fromAnnotatedElement(AnnotatedElement annotated){ScalarFunction scalarFunction = annotated.getAnnotation(ScalarFunction.class);ScalarOperator scalarOperator = annotated.getAnnotation(ScalarOperator.class);Optional<String> description = parseDescription(annotated);ImmutableList.Builder<ScalarImplementationHeader> builder = ImmutableList.builder();if (scalarFunction != null) {String baseName = scalarFunction.value().isEmpty() ? camelToSnake(annotatedName(annotated)) : scalarFunction.value();builder.add(new ScalarImplementationHeader(baseName, new ScalarHeader(description, scalarFunction.hidden(), scalarFunction.deterministic())));for (String alias : scalarFunction.alias()) {builder.add(new ScalarImplementationHeader(alias, new ScalarHeader(description, scalarFunction.hidden(), scalarFunction.deterministic())));}}if (scalarOperator != null) {builder.add(new ScalarImplementationHeader(scalarOperator.value(), new ScalarHeader(description, true, true)));}List<ScalarImplementationHeader> result = builder.build();checkArgument(!result.isEmpty());return result;}

io.trino.operator.scalar.annotations.ScalarImplementationHeader

private static String annotatedName(AnnotatedElement annotatedElement){if (annotatedElement instanceof Class<?>) {return ((Class<?>) annotatedElement).getSimpleName();}if (annotatedElement instanceof Method) {return ((Method) annotatedElement).getName();}checkArgument(false, "Only Classes and Methods are supported as annotated elements.");return null;}

由上可得 method 也是一种 AnnotatedElement

trino 中的 snake 命名法

io.trino.operator.scalar.annotations.ScalarImplementationHeader

private static String camelToSnake(String name){return LOWER_CAMEL.to(LOWER_UNDERSCORE, name);}

com.google.common.base.CaseFormat

  /*** Converts the specified {@code String str} from this format to the specified {@code format}. A* "best effort" approach is taken; if {@code str} does not conform to the assumed format, then* the behavior of this method is undefined but we make a reasonable effort at converting anyway.*/public final String to(CaseFormat format, String str) {checkNotNull(format);checkNotNull(str);return (format == this) ? str : convert(format, str);}

  /** Enum values can override for performance reasons. */String convert(CaseFormat format, String s) {// deal with camel conversionStringBuilder out = null;int i = 0;int j = -1;while ((j = wordBoundary.indexIn(s, ++j)) != -1) {if (i == 0) {// include some extra space for separatorsout = new StringBuilder(s.length() + 4 * format.wordSeparator.length());out.append(format.normalizeFirstWord(s.substring(i, j)));} else {requireNonNull(out).append(format.normalizeWord(s.substring(i, j)));}out.append(format.wordSeparator);i = j + wordSeparator.length();}return (i == 0)? format.normalizeFirstWord(s): requireNonNull(out).append(format.normalizeWord(s.substring(i))).toString();}