java设计模式-创建型模式-建造者模式

场景举例

根据表名、每页条数、偏移量等属性进行拼接组装，并且根据不同的数据库类型生成不同的sql脚本

观察Lombok @Builder注解生成的代码

源码

java 复制代码

package xin.yangshuai.basic01.gof23.builder;

import lombok.Builder;

@Builder
public class DatabaseSqlLombok {

    /**
     * 数据库类型
     */
    private String database;

    /**
     * 表名
     */
    private String tableName;

    /**
     * 每页条数
     */
    private Integer pageSize;

    /**
     * 偏移量
     */
    private Integer offset;

    /**
     * sql
     */
    private String sql;
}

编译后的代码（反编译回java代码）

java 复制代码

package xin.yangshuai.basic01.gof23.builder;

public class DatabaseSqlLombok {
    private String database;
    private String tableName;
    private Integer pageSize;
    private Integer offset;
    private String sql;

    DatabaseSqlLombok(String database, String tableName, Integer pageSize, Integer offset, String sql) {
        this.database = database;
        this.tableName = tableName;
        this.pageSize = pageSize;
        this.offset = offset;
        this.sql = sql;
    }

    public static DatabaseSqlLombokBuilder builder() {
        return new DatabaseSqlLombokBuilder();
    }

    public static class DatabaseSqlLombokBuilder {
        private String database;
        private String tableName;
        private Integer pageSize;
        private Integer offset;
        private String sql;

        DatabaseSqlLombokBuilder() {
        }

        public DatabaseSqlLombokBuilder database(String database) {
            this.database = database;
            return this;
        }

        public DatabaseSqlLombokBuilder tableName(String tableName) {
            this.tableName = tableName;
            return this;
        }

        public DatabaseSqlLombokBuilder pageSize(Integer pageSize) {
            this.pageSize = pageSize;
            return this;
        }

        public DatabaseSqlLombokBuilder offset(Integer offset) {
            this.offset = offset;
            return this;
        }

        public DatabaseSqlLombokBuilder sql(String sql) {
            this.sql = sql;
            return this;
        }

        public DatabaseSqlLombok build() {
            return new DatabaseSqlLombok(this.database, this.tableName, this.pageSize, this.offset, this.sql);
        }

        public String toString() {
            return "DatabaseSqlLombok.DatabaseSqlLombokBuilder(database=" + this.database + ", tableName=" + this.tableName + ", pageSize=" + this.pageSize + ", offset=" + this.offset + ", sql=" + this.sql + ")";
        }
    }
}

建造者模式中的几种角色

产品（Product）

具体的产品

抽象建造者（Builder）

定义创建产品各个部件的方法，通常包括多个创建产品部件的方法和一个返回具体产品的方法

具体建造者（ConcreteBuilder）

实现抽象建造者的接口

指挥者（Director）

控制建造者创建产品各个部件的顺序

代码示例

参考lombok生成的代码，定义建造者模式中的各个角色

产品：DatabaseSql

java 复制代码

package xin.yangshuai.basic01.gof23.builder;

public class DatabaseSql {

    /**
     * 数据库类型
     */
    private String database;

    /**
     * 表名
     */
    private String tableName;

    /**
     * 每页条数
     */
    private Integer pageSize;

    /**
     * 偏移量
     */
    private Integer offset;

    /**
     * sql
     */
    private String sql;

    public DatabaseSql() {
    }

    public DatabaseSql(String database, String tableName, Integer pageSize, Integer offset, String sql) {
        this.database = database;
        this.tableName = tableName;
        this.pageSize = pageSize;
        this.offset = offset;
        this.sql = sql;
    }

    public String getDatabase() {
        return database;
    }

    public void setDatabase(String database) {
        this.database = database;
    }

    public String getTableName() {
        return tableName;
    }

    public void setTableName(String tableName) {
        this.tableName = tableName;
    }

    public Integer getPageSize() {
        return pageSize;
    }

    public void setPageSize(Integer pageSize) {
        this.pageSize = pageSize;
    }

    public Integer getOffset() {
        return offset;
    }

    public void setOffset(Integer offset) {
        this.offset = offset;
    }

    public String getSql() {
        return sql;
    }

    public void setSql(String sql) {
        this.sql = sql;
    }
}

抽象建造者：DatabaseSqlBuilder

java 复制代码

package xin.yangshuai.basic01.gof23.builder;

public interface DatabaseSqlBuilder {

    /**
     * 数据库类型
     *
     * @return
     */
    DatabaseSqlBuilder database();

    /**
     * 表名
     *
     * @param tableName
     * @return
     */
    DatabaseSqlBuilder tableName(String tableName);

    /**
     * 每页条数
     *
     * @param pageSize
     * @return
     */
    DatabaseSqlBuilder pageSize(Integer pageSize);

    /**
     * 偏移量
     *
     * @param offset
     * @return
     */
    DatabaseSqlBuilder offset(Integer offset);

    /**
     * sql
     *
     * @return
     */
    DatabaseSqlBuilder sql();

    /**
     * 生成DatabaseSql
     *
     * @return
     */
    DatabaseSql build();
}

具体建造者：MySQLDatabaseSqlBuilder

java 复制代码

package xin.yangshuai.basic01.gof23.builder;

public class MySQLDatabaseSqlBuilder implements DatabaseSqlBuilder {

    /**
     * 数据库类型
     */
    private String database;

    /**
     * 表名
     */
    private String tableName;

    /**
     * 每页条数
     */
    private Integer pageSize;

    /**
     * 偏移量
     */
    private Integer offset;

    /**
     * sql
     */
    private String sql;

    @Override
    public DatabaseSqlBuilder database() {
        this.database = "MySQL";
        return this;
    }

    public DatabaseSqlBuilder tableName(String tableName) {
        this.tableName = tableName;
        return this;
    }

    public DatabaseSqlBuilder pageSize(Integer pageSize) {
        this.pageSize = pageSize;
        return this;
    }

    public DatabaseSqlBuilder offset(Integer offset) {
        this.offset = offset;
        return this;
    }

    @Override
    public DatabaseSqlBuilder sql() {
        this.sql = "select * from " + tableName + " limit " + offset + "," + pageSize + ";";
        return this;
    }

    @Override
    public DatabaseSql build() {
        return new DatabaseSql(database, tableName, pageSize, offset, sql);
    }
}

指挥者：DatabaseSqlDirector

java 复制代码

package xin.yangshuai.basic01.gof23.builder;

public class DatabaseSqlDirector {

    private DatabaseSqlBuilder databaseSqlBuilder;

    public void setDatabaseSqlBuilder(DatabaseSqlBuilder databaseSqlBuilder) {
        this.databaseSqlBuilder = databaseSqlBuilder;
    }

    public DatabaseSql build(){
        if (databaseSqlBuilder != null) {
            return databaseSqlBuilder.database().sql().build();
        }
        return null;
    }
}

方法调用测试

java 复制代码

package xin.yangshuai.basic01.gof23.builder;

public class Main {

    public static void main(String[] args) {
        DatabaseSqlBuilder databaseSqlBuilder = new MySQLDatabaseSqlBuilder().tableName("test_user").offset(0).pageSize(10);
        DatabaseSqlDirector databaseSqlDirector = new DatabaseSqlDirector();

        databaseSqlDirector.setDatabaseSqlBuilder(databaseSqlBuilder);

        DatabaseSql databaseSql = databaseSqlDirector.build();

        System.out.println(databaseSql.getDatabase());
        System.out.println(databaseSql.getSql());
    }
}

响应信息

log 复制代码

MySQL
select * from test_user limit 0,10;

个人理解

指挥者的作用：设置比较复杂的属性，比如上面例子中设置sql属性（需要其它属性进行组合，拼接），可能需要指挥者类来控制执行的顺序
一般情况应该不需要指挥者类

如有不对，欢迎指正！