Build Dynamic Query

Use Cases

The following is a code example on how to use Lambda express to build dynamic query the where clause. Here is the use cases:

• client provide a set of query parameters in JSON format or XML format
• Mule flow will transform the request payload to java LinkedHashMap
• We need to write custom transformer to build the database query's where clause
• In the custom transformer, we need to filter the entries with null or empty string value
• The transform should return the string in the format of:

      ID='1243124' and Name='John Smith'
     

Code Example

package com.ggl.util;

import java.util.HashMap;
import java.util.LinkedHashMap;

public class DynamicQueryBuilder {
 public static void main(String[] argv) {
  System.out.println("--> Build HashMap Now! <--");
  HashMap source = new LinkedHashMap<>();
  source.put("ID", "123456789");
  source.put("NAME", "Gary Liu");
  source.put("Address", null);
  source.put("Sex", "");
  
  StringBuilder builder = new StringBuilder();
  
  source.entrySet()
   .parallelStream()
   .filter(e->e.getValue() != null)
   .filter(e->e.getValue().length() != 0)
   .forEachOrdered(e -> append(builder, e.getKey(), e.getValue()));
  
  String tmpResult = builder.toString();
  
  System.out.println(tmpResult);
  System.out.println (tmpResult.replaceFirst(" and " + "$", ""));
 }
 
 private static void append(StringBuilder builder, String key, String value) {
  builder.append(key + "='" + value + "' and " );
 }

}