Java设计模式(15)--建造者

 Intent
Separate the construction of a complex object from its representation so that the same construction process can create different representations.
the algorithm for creating a complex object should be independent of the parts that make up the object and how they're assembled.
It isolates code for construction and representation.

 

How to
Director
constructs an object using the Builder interface

 

Builder
specifies an abstract interface for creating parts of a Product object

 

ConcreteBuilder
constructs and assembles parts of the product by implementing the Builder interface.

 

Product

 

Konwn cases
FileFormatConverter
Parser
UI Builder

UML

 

代码样例

 package org.haha.DesignPatterns.builder; public class Test { public static void main(String[] args) { SQLSelectBuilder builder = null; if (args[0].equals("mysql")) { builder = new MysqlSQLSelectBuilder(); } else { builder = new OracleSQLSelectBuilder(); } SQLCreater creater = new SQLCreater(builder); String sql = creater.build( new String[]{"column1", "column2"}, "table", new String[]{"column3", "column4"}, new Object[]{new Integer(1), "haha"}); System.out.println("sql=" + sql); } } package org.haha.DesignPatterns.builder; public class SQLCreater { private SQLSelectBuilder builder; public SQLCreater(SQLSelectBuilder builder) { this.builder = builder; } public String build(String[] queryColumns, String table, String[] whereColumns, Object[] whereParams) { builder.clearSQL(); builder.addQueryColumn(queryColumns); builder.addTable(table); builder.addWhereColumn(whereColumns, whereParams); return builder.getSQL(); } } package org.haha.DesignPatterns.builder; public interface SQLSelectBuilder { void clearSQL(); void addQueryColumn(String[] columns); void addTable(String table); void addWhereColumn(String[] columns, Object[] params); String getSQL(); } package org.haha.DesignPatterns.builder; public class MysqlSQLSelectBuilder implements SQLSelectBuilder { private StringBuilder sql = new StringBuilder(); public void addQueryColumn(String[] columns) { sql.append("SELECT").append(" "); for (int i = 0; i < columns.length; i++) { sql.append("`").append(columns[i]).append("`"); if (i < columns.length - 1) { sql.append(","); } } sql.append(" "); } public void addTable(String table) { sql.append("FROM").append(" `").append(table).append("` "); } public void addWhereColumn(String[] columns, Object[] params) { sql.append("WHERE").append(" "); for (int i = 0; i < columns.length; i++) { sql.append("`").append(columns[i]).append("`"); sql.append("="); if (params[i] instanceof Number) { sql.append(params[i].toString()); } else { sql.append("'").append(params[i].toString()).append("'"); } if (i < columns.length - 1) { sql.append(" AND "); } } } public String getSQL() { return sql.toString(); } public void clearSQL() { int start = 0; int end = sql.length(); if (sql.length() > 0) { sql.delete(start, end); } } } package org.haha.DesignPatterns.builder; public class OracleSQLSelectBuilder implements SQLSelectBuilder { private StringBuilder sql = new StringBuilder(); public void addQueryColumn(String[] columns) { sql.append("SELECT").append(" "); for (int i = 0; i < columns.length; i++) { sql.append(columns[i]); if (i < columns.length - 1) { sql.append(","); } } sql.append(" "); } public void addTable(String table) { sql.append("FROM").append(" ").append(table).append(" "); } public void addWhereColumn(String[] columns, Object[] params) { sql.append("WHERE").append(" "); for (int i = 0; i < columns.length; i++) { sql.append(columns[i]); sql.append("="); if (params[i] instanceof Number) { sql.append(params[i].toString()); } else { sql.append("'").append(params[i].toString()).append("'"); } if (i < columns.length - 1) { sql.append(" AND "); } } } public String getSQL() { return sql.toString(); } public void clearSQL() { int start = 0; int end = sql.length(); if (sql.length() > 0) { sql.delete(start, end); } } }