https://blogs.oracle.com/nashorn/entry/flexible_json_with_nashorn_parser
最近、Hjson（Human JSON：人間向けの構成ファイル形式で、人間がやらかすエラーを減らすことができる）に出くわしました。詳しくは以下のリンクを参照してください。
Hjson, the Human JSONNashorn Parser API (JDK9) を使ってHjsonと同様の柔軟なJSON拡張をNashornでサポートできるかどうか確認しようと考えました。
http://hjson.org
JEP 236: Parser API for Nashorn以下のFlexiJSON.parse実装では、Nashorn Parser APIを使って拡張可能なflexi JSONがデータのみ（つまり、実行コードがない）であり、ことを検証し、その後このflexi JSONからオブジェクトを作成するための評価を実行します。
http://openjdk.java.net/jeps/236
FlexiJSONでできることは以下の通りです。
- 任意の場所に1行、および複数行のコメント
- 引用符で囲まれていないプロパティ名とプロパティ値
- 正規表現のリテラル値
- 末尾のカンマの省略
- Shellスタイルのコメント (#を使ったコメント)
- 複数行の文字列値（UNIXのヒアドキュメントスタイル）
/*
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* modification, are permitted provided that the following conditions
* are met:
*
* - Redistributions of source code must retain the above copyright
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* - Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
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*
* - Neither the name of Oracle nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
* IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
"use strict";
function FlexiJSON() {}
// helper to locate Nashorn Parser API classes
FlexiJSON.treeType = function(name) {
return Java.type("jdk.nashorn.api.tree." + name);
}
// Nashorn Parser API classes used
FlexiJSON.ArrayLiteral = FlexiJSON.treeType("ArrayLiteralTree");
FlexiJSON.ExpressionStatement = FlexiJSON.treeType("ExpressionStatementTree");
FlexiJSON.ObjectLiteral = FlexiJSON.treeType("ObjectLiteralTree");
FlexiJSON.RegExpLiteral = FlexiJSON.treeType("RegExpLiteralTree");
FlexiJSON.Literal = FlexiJSON.treeType("LiteralTree");
FlexiJSON.Parser = FlexiJSON.treeType("Parser");
FlexiJSON.SimpleTreeVisitor = FlexiJSON.treeType("SimpleTreeVisitorES5_1");
// FlexiJSON.parse API
FlexiJSON.parse = function(str) {
var parser = (typeof $OPTIONS == "undefined")?
FlexiJSON.Parser.create() :
FlexiJSON.Parser.create("-scripting");
// force the string to be an expression by putting it inside (, )
str = "(" + str + ")";
var ast = parser.parse("", str, null);
// Should not happen. parse would have thrown syntax error
if (!ast) {
return undefined;
}
// allowed 'literal' values in flexi JSON
function isLiteral(node) {
return node instanceof FlexiJSON.ArrayLiteral ||
node instanceof FlexiJSON.Literal ||
node instanceof FlexiJSON.ObjectLiteral ||
node instanceof FlexiJSON.RegExpLiteral;
}
var visitor;
ast.accept(visitor = new (Java.extend(FlexiJSON.SimpleTreeVisitor)) {
lineMap: null,
throwError: function(msg, node) {
if (this.lineMap) {
var pos = node.startPosition;
var line = this.lineMap.getLineNumber(pos);
var column = this.lineMap.getColumnNumber(pos);
// we introduced extra '(' at start. So, adjust column number
msg = msg + " @ " + line + ":" + (column - 1);
}
throw new TypeError(msg);
},
visitLiteral: function(node, extra) {
print(node.value);
},
visitExpressionStatement: function(node, extra) {
var expr = node.expression;
if (isLiteral(expr)) {
expr.accept(visitor, extra);
} else {
this.throwError("only literals can occur", expr);
}
},
visitArrayLiteral: function(node, extra) {
for each (var elem in node.elements) {
if (isLiteral(elem)) {
elem.accept(visitor, extra);
} else {
this.throwError("only literal array element value allowed", elem);
}
}
},
visitObjectLiteral: function(node, extra) {
for each (var prop in node.properties) {
if (prop.getter != null || prop.setter != null) {
this.throwError("getter/setter property not allowed", node);
}
var value = prop.value;
if (isLiteral(value)) {
value.accept(visitor, extra);
} else {
this.throwError("only literal property value allowed", value);
}
}
},
visitCompilationUnit: function(node, extra) {
this.lineMap = node.lineMap;
var elements = node.sourceElements;
if (elements.length > 1) {
this.throwError("more than one top level expression", node.sourceElements[1]);
}
var stat = node.sourceElements[0];
if (! (stat instanceof FlexiJSON.ExpressionStatement)) {
this.throwError("only one top level expresion allowed", stat);
}
stat.accept(visitor, extra);
},
}, null);
// safe to eval given string as flexi JSON!
return eval(str);
}
FlexiJSON.parseの簡単な利用方法は以下のような感じです。File: fjson.js
var obj = FlexiJSON.parse(<<EOF
// this is a comment
{
foo: 23,
bar: [ 34, 454, 54,],
// inline comment here
/** multi line
comments are fine too! */
# shell style line comment is fine!
regex: /gdfg/i, // regexp literal
str: <<END
Multiple line strings via nashorn
-scripting mode extension as well
END
}
EOF)
print(obj.foo);
print(obj.bar);
print(obj.regex);
print(obj.str);
（訳注）当然ながら、fjson.jsの先頭で
load("flexjson.js")としておかなければ、FlexiJSONが何者かわからないので、必ず追加しておいてください。実行結果はこんな感じです。
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