能有影响elasticsearch score的方法有很多，官方推荐的是使用内置的painless脚本语言结合function_score来重新定义score。由于本人开发的项目其算法是由java语言开发的，于是决定尝试原生脚本开发。
elasticsearch脚本由plugin-descriptor.properties文件以及运行jar包组成，plugin-descriptor.properties主要用来定义版本信息、对应es的版本信息等属性。

官方的例子

<br /> public class ExpertScriptPlugin extends Plugin implements ScriptPlugin {<br /> @Override<br /> public ScriptEngineService getScriptEngineService(Settings settings) {<br /> return new MyExpertScriptEngine();<br /> }<br /> /** An example {@link ScriptEngineService} that uses Lucene segment details to implement pure document frequency scoring. */<br /> // tag::expert_engine<br /> private static class MyExpertScriptEngine implements ScriptEngineService {<br /> @Override<br /> public String getType() {<br /> return "expert_scripts";<br /> }<br /> @Override<br /> public Function<Map<String,Object>,SearchScript> compile(String scriptName, String scriptSource, Map<String, String> params) {<br /> // we use the script "source" as the script identifier<br /> if ("pure_df".equals(scriptSource)) {<br /> return p -> new SearchScript() {<br /> final String field;<br /> final String term;<br /> {<br /> if (p.containsKey("field") == false) {<br /> throw new IllegalArgumentException("Missing parameter [field]");<br /> }<br /> if (p.containsKey("term") == false) {<br /> throw new IllegalArgumentException("Missing parameter [term]");<br /> }<br /> field = p.get("field").toString();<br /> term = p.get("term").toString();<br /> }<br /> @Override<br /> public LeafSearchScript getLeafSearchScript(LeafReaderContext context) throws IOException {<br /> PostingsEnum postings = context.reader().postings(new Term(field, term));<br /> if (postings == null) {<br /> // the field and/or term don't exist in this segment, so always return 0<br /> return () -> 0.0d;<br /> }<br /> return new LeafSearchScript() {<br /> int currentDocid = -1;<br /> @Override<br /> public void setDocument(int docid) {<br /> // advance has undefined behavior calling with a docid <= its current docid<br /> if (postings.docID() < docid) {<br /> try {<br /> postings.advance(docid);<br /> } catch (IOException e) {<br /> throw new UncheckedIOException(e);<br /> }<br /> }<br /> currentDocid = docid;<br /> }<br /> @Override<br /> public double runAsDouble() {<br /> if (postings.docID() != currentDocid) {<br /> // advance moved past the current doc, so this doc has no occurrences of the term<br /> return 0.0d;<br /> }<br /> try {<br /> return postings.freq();<br /> } catch (IOException e) {<br /> throw new UncheckedIOException(e);<br /> }<br /> }<br /> };<br /> }<br /> @Override<br /> public boolean needsScores() {<br /> return false;<br /> }<br /> };<br /> }<br /> throw new IllegalArgumentException("Unknown script name " + scriptSource);<br /> }<br /> <br /> @Override<br /> @SuppressWarnings("unchecked")<br /> public SearchScript search(CompiledScript compiledScript, SearchLookup lookup, @Nullable Map<String, Object> params) {<br /> Function<Map<String,Object>,SearchScript> scriptFactory = (Function<Map<String,Object>,SearchScript>) compiledScript.compiled();<br /> return scriptFactory.apply(params);<br /> }<br /> <br /> @Override<br /> public ExecutableScript executable(CompiledScript compiledScript, @Nullable Map<String, Object> params) {<br /> throw new UnsupportedOperationException();<br /> }<br /> <br /> @Override<br /> public boolean isInlineScriptEnabled() {<br /> return true;<br /> }<br /> <br /> @Override<br /> public void close() {}<br /> }<br /> }<br />

代码解读：
本例在elasticsearch源码中，https://github.com/elastic/ela ... oring

MyExpertScriptEngine类是其中最重要的类，用于实现脚本参数定义，编译，以及打分机制的实现。其中compile方法返回我们定义好打分逻辑的java function。search方法用于我们在搜索过程中实施定义好的打分逻辑。
怎奈笔者对于函数式编程知道的不多（后续需要补课），其实评分逻辑也可以在search方法中实现，于是有了下面的一段代码。

```
public class fieldaddScriptPlugin extends Plugin implements ScriptPlugin {
@Override
public ScriptEngineService getScriptEngineService(Settings settings) {
return new MyExpertScriptEngine();
}
private static class MyExpertScriptEngine implements ScriptEngineService {
@Override
public String getType() {
return "expert_scripts";
}

@Override
public Object compile(String scriptName, String scriptSource, Map<String, String> params) {
if ("example_add".equals(scriptSource)) {
return scriptSource;
}
throw new IllegalArgumentException("Unknown script name " + scriptSource);
}

@Override
@SuppressWarnings("unchecked")
public SearchScript search(CompiledScript compiledScript, SearchLookup lookup, @Nullable Map<String, Object> vars) {

/**

• 校验输入参数，DSL中params 参数列表
  */
  final long inc;
  final String fieldname;
  if (vars == null || vars.containsKey("inc") == false) {
  inc = 0;
  } else {
  inc = ((Number) vars.get("inc")).longValue();
  }
  
  if (vars == null || vars.containsKey("fieldname") == false) {
  throw new IllegalArgumentException("Missing parameter [fieldname]");
  } else {
  fieldname = (String) vars.get("fieldname");
  }
  
  return new SearchScript() {
  @Override
  public LeafSearchScript getLeafSearchScript(LeafReaderContext context) throws IOException {
  final LeafSearchLookup leafLookup = lookup.getLeafSearchLookup(context);
  
  
  return new LeafSearchScript() {
  @Override
  public void setDocument(int doc) {
  if (leafLookup != null) {
  leafLookup.setDocument(doc);
  }
  }
  
  @Override
  public double runAsDouble() {
  long values = 0;
  /**
  
  • 获取document中字段内容
    */
    for (Object v : (List<?>) leafLookup.doc().get(fieldname)) {
    values = ((Number) v).longValue() + values;
    }
    return values + inc;
    }
    };
    }
    
    @Override
    public boolean needsScores() {
    return false;
    }
    };
    }
    <br /> <br /> 这段代码的逻辑是把给定的字段(字段类型long)的每个元素相加后再加上给定的增量参数最后形成score分值。为了实现上述逻辑需要实现参数获取、根据给定的字段名获取内容列表量的关键件。下面结合代码说说这两个步骤如何实现的。<br /> search方法中Map<String, Object> vars参数对应DSL中"params"参数，用于接受实际给定的运行时参数。SearchLookup lookup参数由系统传入，通过lookup.getLeafSearchLookup(context)获取LeafSearchLookup通过该对象可以获取给定字段的值。<br /> <br /> 对于elasticsearch 2.x以前的版本可以通过NativeScriptFactory实现原生脚本。<br /> <br />
    public class MyNativeScriptPlugin extends Plugin implements ScriptPlugin {
    private final static Logger LOGGER = LogManager.getLogger(MyFirstPlugin.class);
    
    
    public MyNativeScriptPlugin() {
    super();
    LOGGER.warn("This is MyNativeScriptPlugin");
    }
    
    @Override
    public List getNativeScripts() {
    return Collections.singletonList(new MyNativeScriptFactory());
    }
    
    
    public static class MyNativeScriptFactory implements NativeScriptFactory {
    @Override
    public ExecutableScript newScript(@Nullable Map<String, Object> params) {
    
    
    // return new MyNativeScript();
    return new AbstractDoubleSearchScript(){
    
    
    @Override
    public double runAsDouble() {
    int b=0;
    if(params.get("add")!=null){
    b= (int) params.get("add");
    }
    
    
    String s = source().get("last").toString();
    double a = s.length()+b;
    return a; }
    };
    }
    
    
    @Override
    public boolean needsScores() {
    return false;
    }
    
    
    @Override
    public String getName() {
    return "my_script";
    }
    }
    }
    ```
    
    工程组织
    elasticsearch工程使用gradle进行依赖管理和生命周期管理，为此es项目自己也开发了esplugin的gradle插件，但不兼容gradle4.2以上的版本。参考github中的成熟插件，使用maven组织工程。
    
    主要涉及两个文件
    pom.xml
    plugin.xml
    工程利用maven-assembly-plugin打包jar。
    
    本例github地址：https://github.com/jiashiwen/e ... ample
    欢迎点赞或拍砖