设计模式-建造者模式

设计模式-建造者模式

建造者模式是将一个复杂对象的构建与它的表示分离，使得同样的构建过程可以创建不同的表示。

用户只需要指定需要建造的类型就可以获得对象，建造过程和细节不需要了解。

例子：

package com.black.design.pattern.builder.sql;

import java.util.ArrayList;
import java.util.List;
// 查询规则类
public class QueryRule {

	// 查询条件
	private List<String> conditions = new ArrayList<String>();
	// 排序字段
	private List<String> orderConditions = new ArrayList<String>();
	// 参数值
	private List<Object> params = new ArrayList<Object>();
	
	public QueryRule addAscOrder(String propertyName) {
		orderConditions.add(propertyName + " asc");
		return this;
	}
	
	public QueryRule addDescOrder(String propertyName, Object v) {
		orderConditions.add(propertyName + " desc");
		return this;
	}
	
	public QueryRule andLike(String propertyName, Object v) {
		params.add("%"+v+"%");
		conditions.add(propertyName + " like ");
		return this;
	}
	
	public QueryRule andEquals(String propertyName, Object v) {
		params.add(v);
		conditions.add(propertyName + " = ");
		return this;
	}
	
	public QueryRule andGreaterEquals(String propertyName, Object v) {
		params.add(v);
		conditions.add(propertyName + " >= ");
		return this;
	}

	public List<String> getConditions() {
		return conditions;
	}

	public List<String> getOrderConditions() {
		return orderConditions;
	}

	public List<Object> getParams() {
		return params;
	}
}

package com.black.design.pattern.builder.sql;

import java.util.ArrayList;
import java.util.List;
// sql 构造器
public class QueryRuleSqlBuilder {
	
	private QueryRule queryRule;
	
	private List<Object> values = new ArrayList<Object>();
	
	public QueryRuleSqlBuilder(QueryRule queryRule) {
		this.queryRule = queryRule;
		this.values = queryRule.getParams();
	}
	

	public String build(String tableName) {
		StringBuffer sqlBuffer = new StringBuffer();
		sqlBuffer.append("select * from ").append(tableName);
		List<String> conditions = queryRule.getConditions();
		for (int i = 0; i < conditions.size(); i++) {
			if(i==0) {
				sqlBuffer.append(" where ");
			}
			sqlBuffer.append(conditions.get(i)).append("?");
			if(i < conditions.size() - 1) {
				sqlBuffer.append(" and ");
			}
		}
		
		//排序
		List<String> orders =  queryRule.getOrderConditions();
		for (int i = 0; i < orders.size(); i++) {
			
			if(i==0) {
				sqlBuffer.append(" order by ");
			}
			sqlBuffer.append(orders.get(i));
			if(i < orders.size() - 1) {
				sqlBuffer.append(",");
			}
		}
		sqlBuffer.append(";");
		return sqlBuffer.toString();
	}

	public List<Object> getValues() {
		return values;
	}
}

测试：

package com.black.design.pattern.builder.sql;

public class QueryRuleSqlBuilderTest {
	
	public static void main(String[] args) {
		
		QueryRule queryRule = new QueryRule();
		queryRule.addAscOrder("age");
		queryRule.andEquals("addr", "北京市");
		queryRule.andLike("name", "black");
		queryRule.andGreaterEquals("age", 18);
		queryRule.andGreaterEquals("time", "2021-01-01");
		
		QueryRuleSqlBuilder builder = new QueryRuleSqlBuilder(queryRule);
		System.out.println(builder.build("t_user"));
		
		System.out.println(builder.getValues());
		
	}
}

输出：

select * from t_user where addr = ? and name like ? and age >= ? and time >= ? order by age asc;
[北京市, %black%, 18, 2021-01-01]