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This article shows you how Spring JPA repository customizes the data converter, which is concise and easy to understand, which will definitely brighten your eyes. I hope you can get something through the detailed introduction of this article.

We all know that when using the methods in jpaRepository, the returned data format is either entity mapped to the database table, or Projection interface, or map, or basic data types. If you want to customize a class to receive data, a type conversion error is thrown. Where there is demand, there is motivation.

Recently, when I was working on a project, I wanted to reuse the vo class to receive the returned data from Repository, but spirngjpa did not recognize it, so after Baidu failed, I started the debug execution process. The hard work lived up to the dedicated people, and found a way to convert data. All the secrets are in this class, DefaultConversionService. The screenshots are as follows

That is to say, if I customize a converter and register it in this ConversionService, then I can be 'obscene' in my own convert.

First of all, take a look at the first method of the screenshot, as the name implies, you can get an example of his sharing! It is obvious that it is a window for us. Needless to say, here are the usage methods and my custom convert

/ / springboot startup class public static void main (String [] args) {SpringApplication.run (Application.class, args); ((DefaultConversionService) DefaultConversionService.getSharedInstance ()) .addConverter (new MyConverter ());} / / MyConverter.javaimport lombok.extern.slf4j.Slf4j;import org.springframework.core.convert.TypeDescriptor;import org.springframework.core.convert.converter.GenericConverter;import org.springframework.util.ConcurrentReferenceHashMap;import sun.reflect.misc.MethodUtil Import java.lang.reflect.Method;import java.math.BigInteger;import java.util.HashSet;import java.util.Map;import java.util.Set;import java.util.stream.Stream;/** *. Custom object Converter * * / @ Slf4jpublic class RdeConverter implements GenericConverter {private final Map methodCache = new ConcurrentReferenceHashMap (2 > > 6); private final CacheMethod NO_MATCH = new CacheMethod (null); @ Override public Set getConvertibleTypes () {ConvertiblePair pair = new ConvertiblePair (Map.class, RdeConvertible.class); Set set = new HashSet (); set.add (pair); return set } @ Override public Object convert (Object source, TypeDescriptor sourceType, TypeDescriptor targetType) {try {log.debug ("* * begin convert {} to {}", sourceType, targetType); Map map = (Map) source; Object o = targetType.getType (). NewInstance (); for (Object fieldName: map.keySet ()) {String name = getMethodName (fieldName.toString ()) String mName = o.getClass (). GetName (). Concat ("."). Concat (name); CacheMethod cacheMethod = methodCache.get (mName) If (cacheMethod = = null) {/ / FIXME if there is a method overload, there may be an exception Method method = Stream.of (MethodUtil.getPublicMethods (targetType.getType () .filter (m-> m.getName () .equalsIgnoreCase (name)) .findFirst () .orElse (null) CacheMethod = method = = null? NO_MATCH: new CacheMethod (method); methodCache.put (mName, cacheMethod);} if (cacheMethod! = NO_MATCH) {try {Method method = cacheMethod.get (); method.invoke (o, caseParam (map.get (fieldName), method.getParameterTypes () [0])) } catch (Exception e) {log.error (e.getMessage (), e);} return o;} catch (Exception e) {log.error (e.getMessage (), e);} return null } private Object caseParam (Object param, Class paramType) {if (param instanceof BigInteger) {if (param.getClass () = = paramType) {return param;} if (paramType = = Integer.class) {return ((BigInteger) param) .intValue () } if (paramType = = Long.class) {return ((BigInteger) param) .longValue ();} return param;} return param;} private String getMethodName (String fieldName) {String [] s = fieldName.trim () .split ("_") If (s.length > 1) {String m = Stream.of (s). Reduce ((a, b)-> firstToUp (a) + firstToUp (b)) .get (); return "set" .concat (m);} return "set" .concat (firstToUp (s [0])) } private String firstToUp (String s) {if (s.length () > 1) {return s.substring (0,1). ToUpperCase (). Concat (s.substring (1));} return s.toUpperCase ();} class CacheMethod {private Method method; CacheMethod (Method method) {this.method = method } Method get () {return this.method;}} / / RdeConvertible.java/** *. Conversion type tag * * / public interface RdeConvertible {}

Use screenshots:

The above is how Spring JPA repository customizes data converter. Have you learned any knowledge or skills? If you want to learn more skills or enrich your knowledge reserve, you are welcome to follow the industry information channel.

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