使用脚本引擎的高级脚本
edit使用脚本引擎的高级脚本
edit一个 ScriptEngine 是实现脚本语言的后端。它也可以用于编写需要使用脚本高级内部功能的脚本。例如，一个想要在评分时使用词频的脚本。
插件的文档提供了更多关于如何编写插件以使Elasticsearch正确加载的信息。要注册ScriptEngine，您的插件应实现ScriptPlugin接口并覆盖getScriptEngine(Settings settings)方法。
以下是一个自定义的 ScriptEngine 示例，它使用了语言名称 expert_scripts。它实现了一个名为 pure_df 的脚本，该脚本可以用作搜索脚本来覆盖每个文档的分数，作为所提供术语的文档频率。
private static class MyExpertScriptEngine implements ScriptEngine {
@Override
public String getType() {
return "expert_scripts";
}
@Override
public <T> T compile(
String scriptName,
String scriptSource,
ScriptContext<T> context,
Map<String, String> params
) {
if (context.equals(ScoreScript.CONTEXT) == false) {
throw new IllegalArgumentException(getType()
+ " scripts cannot be used for context ["
+ context.name + "]");
}
// we use the script "source" as the script identifier
if ("pure_df".equals(scriptSource)) {
ScoreScript.Factory factory = new PureDfFactory();
return context.factoryClazz.cast(factory);
}
throw new IllegalArgumentException("Unknown script name "
+ scriptSource);
}
@Override
public void close() {
// optionally close resources
}
@Override
public Set<ScriptContext<?>> getSupportedContexts() {
return Set.of(ScoreScript.CONTEXT);
}
private static class PureDfFactory implements ScoreScript.Factory,
ScriptFactory {
@Override
public boolean isResultDeterministic() {
// PureDfLeafFactory only uses deterministic APIs, this
// implies the results are cacheable.
return true;
}
@Override
public LeafFactory newFactory(
Map<String, Object> params,
SearchLookup lookup
) {
return new PureDfLeafFactory(params, lookup);
}
}
private static class PureDfLeafFactory implements LeafFactory {
private final Map<String, Object> params;
private final SearchLookup lookup;
private final String field;
private final String term;
private PureDfLeafFactory(
Map<String, Object> params, SearchLookup lookup) {
if (params.containsKey("field") == false) {
throw new IllegalArgumentException(
"Missing parameter [field]");
}
if (params.containsKey("term") == false) {
throw new IllegalArgumentException(
"Missing parameter [term]");
}
this.params = params;
this.lookup = lookup;
field = params.get("field").toString();
term = params.get("term").toString();
}
@Override
public boolean needs_score() {
return false; // Return true if the script needs the score
}
@Override
public boolean needs_termStats() {
return false; // Return true if the script needs term statistics via get_termStats()
}
@Override
public ScoreScript newInstance(DocReader docReader)
throws IOException {
DocValuesDocReader dvReader = DocValuesDocReader) docReader); PostingsEnum postings = dvReader.getLeafReaderContext() .reader().postings(new Term(field, term;
if (postings == null) {
/*
* the field and/or term don't exist in this segment,
* so always return 0
*/
return new ScoreScript(params, lookup, docReader) {
@Override
public double execute(
ExplanationHolder explanation
) {
if(explanation != null) {
explanation.set("An example optional custom description to explain details for this script's execution; we'll provide a default one if you leave this out.");
}
return 0.0d;
}
};
}
return new ScoreScript(params, lookup, docReader) {
int currentDocid = -1;
@Override
public void setDocument(int docid) {
/*
* advance has undefined behavior calling with
* a docid <= its current docid
*/
if (postings.docID() < docid) {
try {
postings.advance(docid);
} catch (IOException e) {
throw new UncheckedIOException(e);
}
}
currentDocid = docid;
}
@Override
public double execute(ExplanationHolder explanation) {
if(explanation != null) {
explanation.set("An example optional custom description to explain details for this script's execution; we'll provide a default one if you leave this out.");
}
if (postings.docID() != currentDocid) {
/*
* advance moved past the current doc, so this
* doc has no occurrences of the term
*/
return 0.0d;
}
try {
return postings.freq();
} catch (IOException e) {
throw new UncheckedIOException(e);
}
}
};
}
}
}
您可以通过将脚本的 lang 指定为 expert_scripts，并将脚本的名称指定为脚本源来执行脚本：
POST /_search
{
"query": {
"function_score": {
"query": {
"match": {
"body": "foo"
}
},
"functions": [
{
"script_score": {
"script": {
"source": "pure_df",
"lang" : "expert_scripts",
"params": {
"field": "body",
"term": "foo"
}
}
}
}
]
}
}
}