Implementing an ORM framework against SQL injection with builder mode

This article is excerpted from 《 This is how design patterns should be learned 》

1 The chain style of builder's mode

Take building a course as an example , A complete course consists of PPT Courseware 、 Play back the video 、 Class notes 、 After class homework composition , But the setting order of these contents can be adjusted at will , Let's use the builder model to understand . First create a product class Course.

@Data
public class Course {

    private String name;
    private String ppt;
    private String video;
    private String note;

    private String homework;

    @Override
    public String toString() {
        return "CourseBuilder{" +
                "name='" + name + '\'' +
                ", ppt='" + ppt + '\'' +
                ", video='" + video + '\'' +
                ", note='" + note + '\'' +
                ", homework='" + homework + '\'' +
                '}';
    }
}

Then create the builder class CourseBuilder, Encapsulate the complex creation process , The creation steps are determined by the user .

public class CourseBuilder {

    private Course course = new Course();

    public CourseBuilder addName(String name){
        course.setName(name);
        return this;
    }

    public CourseBuilder addPpt(String ppt){
        course.setPpt(ppt);
        return this;
    }

    public CourseBuilder addVideo(String video){
        course.setVideo(video);
        return this;
    }

    public CourseBuilder addNote(String note){
        course.setNote(note);
        return this;
    }

    public CourseBuilder addHomework(String homework){
        course.setHomework(homework);
        return this;
    }

    public Course builder(){
        return course;
    }

}

Finally, write client test code .

    public static void main(String[] args) {
        CourseBuilder builder = new CourseBuilder()
                    .addName(" Design patterns ")
                    .addPPT("【PPT Courseware 】")
                    .addVideo("【 Play back the video 】")
                    .addNote("【 Class notes 】")
                    .addHomework("【 Homework after class 】");

        System.out.println(builder.build());
}

Does this look familiar ？ Later, when we analyze the application of builder pattern in the framework source code, we will understand . Let's look at the changes of class diagram , As shown in the figure below .

image.png

2 Use static inner classes to implement the builder pattern

in fact , In ordinary coding , We usually ignore the complexity of objects , Priority is given to using factory mode to create objects , Not the builder model . Because the function of factory pattern and builder pattern is to create a product object , The structure of factory mode is more concise and direct （ No, Builder and Director）, So use more often .

In general , We are more used to using static inner classes to implement the builder pattern , That is, a product class automatically has a specific builder , It is responsible for the assembly and creation of the product , No longer need Builder and Director, such , The relationship between product representation and creation is closer , More compact structure , At the same time, it makes the form of builder mode more concise .

If the builder pattern is implemented in the form of static inner classes , Then the previous case can be rewritten as follows .

@Data
public class Course {
    private String name;
    private String ppt;
    private String video;
    private String note;

    private String homework;

    @Override
    public String toString() {
        return "Course{" +
                "name='" + name + '\'' +
                ", ppt='" + ppt + '\'' +
                ", video='" + video + '\'' +
                ", note='" + note + '\'' +
                ", homework='" + homework + '\'' +
                '}';
    }

    public static class Builder {

        private Course course = new Course();

        public Builder addName(String name){
            course.setName(name);
            return this;
        }

        public Builder addPpt(String ppt){
            course.setPpt(ppt);
            return this;
        }

        public Builder addVideo(String video){
            course.setVideo(video);
            return this;
        }

        public Builder addNote(String note){
            course.setNote(note);
            return this;
        }

        public Builder addHomework(String homework){
            course.setHomework(homework);
            return this;
        }

        public Course builder(){
            return course;
        }

    }
}

The client test code is as follows .

    public static void main(String[] args) {
         Course course = new Course.Builder()
                .addName(" Design patterns ")
                .addPpt("【PPT Courseware 】")
                .addVideo("【 Video recording 】")
                 .builder();

        System.out.println(course);
    }
		

such , The code will also look more concise , It won't make people feel that there is another class .

3 Use the builder pattern to dynamically build SQL sentence

Let's take a practical case , This case refers to the open source framework JPA Of SQL Construction pattern . We're building SQL When you query the conditions , It needs to be spliced according to different conditions SQL character string . If the query conditions are complex , be SQL The process of stitching can also become very complicated , This brings great difficulties to code maintenance . therefore , We use the builder class QueryRuleSqlBuilder The complex SQL The construction process is encapsulated , use QueryRule Objects are kept exclusively SQL Query conditions , Finally, according to the query conditions , Automatic generation SQL sentence . First create QueryRule class , The code is as follows .

import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;

/**
 * QueryRule, The main function is used to construct query conditions 
 * 
 * @author Tom
 */
public final class QueryRule implements Serializable
{
	private static final long serialVersionUID = 1L;
	public static final int ASC_ORDER = 101;
	public static final int DESC_ORDER = 102;
	public static final int LIKE = 1;
	public static final int IN = 2;
	public static final int NOTIN = 3;
	public static final int BETWEEN = 4;
	public static final int EQ = 5;
	public static final int NOTEQ = 6;
	public static final int GT = 7;
	public static final int GE = 8;
	public static final int LT = 9;
	public static final int LE = 10;
	public static final int ISNULL = 11;
	public static final int ISNOTNULL = 12;
	public static final int ISEMPTY = 13;
	public static final int ISNOTEMPTY = 14;
	public static final int AND = 201;
	public static final int OR = 202;
	private List<Rule> ruleList = new ArrayList<Rule>();
	private List<QueryRule> queryRuleList = new ArrayList<QueryRule>();
	private String propertyName;

	private QueryRule() {}

	private QueryRule(String propertyName) {
		this.propertyName = propertyName;
	}

	public static QueryRule getInstance() {
		return new QueryRule();
	}
	
	/**
	 *  Add ascending rules 
	 * @param propertyName
	 * @return
	 */
	public QueryRule addAscOrder(String propertyName) {
		this.ruleList.add(new Rule(ASC_ORDER, propertyName));
		return this;
	}

	/**
	 *  Add descending rule 
	 * @param propertyName
	 * @return
	 */
	public QueryRule addDescOrder(String propertyName) {
		this.ruleList.add(new Rule(DESC_ORDER, propertyName));
		return this;
	}

	public QueryRule andIsNull(String propertyName) {
		this.ruleList.add(new Rule(ISNULL, propertyName).setAndOr(AND));
		return this;
	}

	public QueryRule andIsNotNull(String propertyName) {
		this.ruleList.add(new Rule(ISNOTNULL, propertyName).setAndOr(AND));
		return this;
	}

	public QueryRule andIsEmpty(String propertyName) {
		this.ruleList.add(new Rule(ISEMPTY, propertyName).setAndOr(AND));
		return this;
	}

	public QueryRule andIsNotEmpty(String propertyName) {
		this.ruleList.add(new Rule(ISNOTEMPTY, propertyName).setAndOr(AND));
		return this;
	}

	public QueryRule andLike(String propertyName, Object value) {
		this.ruleList.add(new Rule(LIKE, propertyName, new Object[] { value }).setAndOr(AND));
		return this;
	}

	public QueryRule andEqual(String propertyName, Object value) {
		this.ruleList.add(new Rule(EQ, propertyName, new Object[] { value }).setAndOr(AND));
		return this;
	}

	public QueryRule andBetween(String propertyName, Object... values) {
		this.ruleList.add(new Rule(BETWEEN, propertyName, values).setAndOr(AND));
		return this;
	}

	public QueryRule andIn(String propertyName, List<Object> values) {
		this.ruleList.add(new Rule(IN, propertyName, new Object[] { values }).setAndOr(AND));
		return this;
	}

	public QueryRule andIn(String propertyName, Object... values) {
		this.ruleList.add(new Rule(IN, propertyName, values).setAndOr(AND));
		return this;
	}
	
	public QueryRule andNotIn(String propertyName, List<Object> values) {
		this.ruleList.add(new Rule(NOTIN, 
									propertyName, 
									new Object[] { values }).setAndOr(AND));
		return this;
	}

	// Part of the code is omitted here 
	

	public List<Rule> getRuleList() {
		return this.ruleList;
	}

	public List<QueryRule> getQueryRuleList() {
		return this.queryRuleList;
	}

	public String getPropertyName() {
		return this.propertyName;
	}

	protected class Rule implements Serializable {
		private static final long serialVersionUID = 1L;
		private int type;	// Type of rule 
		private String property_name;
		private Object[] values;
		private int andOr = AND;

		public Rule(int paramInt, String paramString) {
			this.property_name = paramString;
			this.type = paramInt;
		}

		public Rule(int paramInt, String paramString,
				Object[] paramArrayOfObject) {
			this.property_name = paramString;
			this.values = paramArrayOfObject;
			this.type = paramInt;
		}
		
		public Rule setAndOr(int andOr){
			this.andOr = andOr;
			return this;
		}
		
		public int getAndOr(){
			return this.andOr;
		}

		public Object[] getValues() {
			return this.values;
		}

		public int getType() {
			return this.type;
		}

		public String getPropertyName() {
			return this.property_name;
		}
	}
}

Then create QueryRuleSqlBuilder class .

package com.tom.vip.pattern.builder.sql;


/**
 *  according to QueryRule An automated build SQL sentence 
 * @author Tom
 *
 */
public class QueryRuleSqlBuilder {
	private int CURR_INDEX = 0; // Record the location of the parameter 
	private List<String> properties; // Save the list of column names 
	private List<Object> values; // Save the parameter value list 
	private List<Order> orders; // Save the collation list 
	
	private String whereSql = ""; 
	private String orderSql = "";
	private Object [] valueArr = new Object[]{};
	private Map<Object,Object> valueMap = new HashMap<Object,Object>();
	
	/**
	 *  Get query conditions 
	 * @return
	 */
	private String getWhereSql(){
		return this.whereSql;
	}
	
	/**
	 *  Get sort criteria 
	 * @return
	 */
	private String getOrderSql(){
		return this.orderSql;
	}
	
	/**
	 *  Get a list of parameter values 
	 * @return
	 */
	public Object [] getValues(){
		return this.valueArr;
	}
	
	/**
	 *  Get a list of parameters 
	 * @return
	 */
	private Map<Object,Object> getValueMap(){
		return this.valueMap;
	}
	
	/**
	 *  establish SQL Constructors 
	 * @param queryRule
	 */
	public QueryRuleSqlBuilder(QueryRule queryRule) {
		CURR_INDEX = 0;
		properties = new ArrayList<String>();
		values = new ArrayList<Object>();
		orders = new ArrayList<Order>();
		for (QueryRule.Rule rule : queryRule.getRuleList()) {
			switch (rule.getType()) {
			case QueryRule.BETWEEN:
				processBetween(rule);
				break;
			case QueryRule.EQ:
				processEqual(rule);
				break;
			case QueryRule.LIKE:
				processLike(rule);
				break;
			case QueryRule.NOTEQ:
				processNotEqual(rule);
				break;
			case QueryRule.GT:
				processGreaterThen(rule);
				break;
			case QueryRule.GE:
				processGreaterEqual(rule);
				break;
			case QueryRule.LT:
				processLessThen(rule);
				break;
			case QueryRule.LE:
				processLessEqual(rule);
				break;
			case QueryRule.IN:
				processIN(rule);
				break;
			case QueryRule.NOTIN:
				processNotIN(rule);
				break;
			case QueryRule.ISNULL:
				processIsNull(rule);
				break;
			case QueryRule.ISNOTNULL:
				processIsNotNull(rule);
				break;
			case QueryRule.ISEMPTY:
				processIsEmpty(rule);
				break;
			case QueryRule.ISNOTEMPTY:
				processIsNotEmpty(rule);
				break;
			case QueryRule.ASC_ORDER:
				processOrder(rule);
				break;
			case QueryRule.DESC_ORDER:
				processOrder(rule);
				break;
			default:
				throw new IllegalArgumentException("type"+rule.getType()+"not supported.");
			}
		}
		// assemble where sentence 
		appendWhereSql();
		// Assemble sort statements 
		appendOrderSql();
		// Assembly parameter value 
		appendValues();
	}
	
	/**
	 *  Get rid of order
	 * 
	 * @param sql
	 * @return
	 */
	private String removeOrders(String sql) {
		Pattern p = Pattern.compile("order\\s*by[\\w|\\W|\\s|\\S]*", Pattern.CASE_INSENSITIVE);
		Matcher m = p.matcher(sql);
		StringBuffer sb = new StringBuffer();
		while (m.find()) {
			m.appendReplacement(sb, "");
		}
		m.appendTail(sb);
		return sb.toString();
	}
	
	/**
	 *  Get rid of select
	 * 
	 * @param sql
	 * @return
	 */
	private String removeSelect(String sql) {
		if(sql.toLowerCase().matches("from\\s+")){
			int beginPos = sql.toLowerCase().indexOf("from");
			return sql.substring(beginPos);
		}else{
			return sql;
		}
	}
	
	/**
	 *  Handle like
	 * @param rule
	 */
	private  void processLike(QueryRule.Rule rule) {
		if (ArrayUtils.isEmpty(rule.getValues())) {
			return;
		}
		Object obj = rule.getValues()[0];

		if (obj != null) {
			String value = obj.toString();
			if (!StringUtils.isEmpty(value)) {
				value = value.replace('*', '%');
				obj = value;
			}
		}
		add(rule.getAndOr(),rule.getPropertyName(),"like","%"+rule.getValues()[0]+"%");
	}

	/**
	 *  Handle between
	 * @param rule
	 */
	private  void processBetween(QueryRule.Rule rule) {
		if ((ArrayUtils.isEmpty(rule.getValues()))
				|| (rule.getValues().length < 2)) {
			return;
		}
		add(rule.getAndOr(),rule.getPropertyName(),"","between",rule.getValues()[0],"and");
		add(0,"","","",rule.getValues()[1],"");
	}
	

// Part of the code is omitted here 
	
	
	/**
	 *  Join in SQL Query rule queue 
	 * @param andOr and perhaps or
	 * @param key  Name 
	 * @param split  Interval between column name and value 
	 * @param value  value 
	 */
	private  void add(int andOr,String key,String split ,Object value){
		add(andOr,key,split,"",value,"");
	}
	
	/**
	 *  Join in SQL Query rule queue 
	 * @param andOr and perhaps or
	 * @param key  Name 
	 * @param split  Interval between column name and value 
	 * @param prefix  Value prefix 
	 * @param value  value 
	 * @param suffix  Value suffix 
	 */
	private  void add(int andOr,String key,String split ,String prefix,Object value,String  	suffix){
		String andOrStr = (0 == andOr ? "" :(QueryRule.AND == andOr ? " and " : " or "));  
		properties.add(CURR_INDEX, 
		 andOrStr + key + " " + split + prefix + (null != value ? " ? " : " ") + suffix);
		if(null != value){
			values.add(CURR_INDEX,value);
			CURR_INDEX ++;
		}
	}
	
	
	/**
	 *  assemble where sentence 
	 */
	private void appendWhereSql(){
		StringBuffer whereSql = new StringBuffer();
		for (String p : properties) {
			whereSql.append(p);
		}
		this.whereSql = removeSelect(removeOrders(whereSql.toString()));
	}
	
	/**
	 *  Assemble sort statements 
	 */
	private void appendOrderSql(){
		StringBuffer orderSql = new StringBuffer();
		for (int i = 0 ; i < orders.size(); i ++) {
			if(i > 0 && i < orders.size()){
				orderSql.append(",");
			}
			orderSql.append(orders.get(i).toString());
		}
		this.orderSql = removeSelect(removeOrders(orderSql.toString()));
	}
	
	/**
	 *  Assembly parameter value 
	 */
	private void appendValues(){
		Object [] val = new Object[values.size()];
		for (int i = 0; i < values.size(); i ++) {
			val[i] = values.get(i);
			valueMap.put(i, values.get(i));
		}
		this.valueArr = val;
	}

	public String builder(String tableName){
		String ws = removeFirstAnd(this.getWhereSql());
		String whereSql = ("".equals(ws) ? ws : (" where " + ws));
		String sql = "select * from " + tableName + whereSql;
		Object [] values = this.getValues();
		String orderSql = this.getOrderSql();
		orderSql = (StringUtils.isEmpty(orderSql) ? " " : (" order by " + orderSql));
		sql += orderSql;
		return sql;
	}


	private String removeFirstAnd(String sql){
		if(StringUtils.isEmpty(sql)){return sql;}
		return sql.trim().toLowerCase().replaceAll("^\\s*and", "") + " ";
	}

}

Then create a Order class .

/**
 * SQL Sort components 
 * @author Tom
 */
public class Order {
	private boolean ascending; // Ascending or descending 
	private String propertyName; // Which field is in ascending order , Which field is in descending order 
	
	public String toString() {
		return propertyName + ' ' + (ascending ? "asc" : "desc");
	}

	/**
	 * Constructor for Order.
	 */
	protected Order(String propertyName, boolean ascending) {
		this.propertyName = propertyName;
		this.ascending = ascending;
	}

	/**
	 * Ascending order
	 *
	 * @param propertyName
	 * @return Order
	 */
	public static Order asc(String propertyName) {
		return new Order(propertyName, true);
	}

	/**
	 * Descending order
	 *
	 * @param propertyName
	 * @return Order
	 */
	public static Order desc(String propertyName) {
		return new Order(propertyName, false);
	}

}

Finally, write client test code .

public static void main(String[] args) {
        QueryRule queryRule = QueryRule.getInstance();
        queryRule.addAscOrder("age");
        queryRule.andEqual("addr","Changsha");
        queryRule.andLike("name","Tom");
        QueryRuleSqlBuilder builder = new QueryRuleSqlBuilder(queryRule);

        System.out.println(builder.builder("t_member"));

        System.out.println("Params: " + Arrays.toString(builder.getValues()));


}

thus , The client code is very clear , The results are shown in the following figure .

image.png

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