在java中进行SQL拼接是一件无比痛苦的工作，这是由于需要通过判断参数动态生成SQL
而且拼接时产生满屏幕的加号或者append，使SQL几乎失去了可读性，那么丢失WHERE，AND，逗号等语法错误将随之而来
最近研究mybatis时发现了一个非常好用的工具类 SQL Builder 1
示例
@Test
public void test(){
String sql = new SQL(){ {
SELECT("name");
SELECT("password");
SELECT("sex");
FROM("student s");
INNER_JOIN("info i on s.id = i.id");
WHERE(String.format("name = '%s'","HanMeiMei"));
} }.toString();
System.out.println(sql);
}
运行结果为：
SELECT name, password, sex
FROM student s
INNER JOIN info i on s.id = i.id
WHERE (name = 'HanMeiMei' AND i.sex = 1)
SQL的拼接词都自动生成了
源码
事实上不必为了使用这个类而引入Mybatis，SQL Builder非常简单，简单到没有使用任何第三方类库，只需将这个类复制粘贴一下就可以直接用了。
SQL Builder 全部代码
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
public abstract class AbstractSQL<T> {
private static final String AND = ") \nAND (";
private static final String OR = ") \nOR (";
public abstract T getSelf();
public T UPDATE(String table) {
sql().statementType = SQLStatement.StatementType.UPDATE;
sql().tables.add(table);
return getSelf();
}
public T SET(String sets) {
sql().sets.add(sets);
return getSelf();
}
public T INSERT_INTO(String tableName) {
sql().statementType = SQLStatement.StatementType.INSERT;
sql().tables.add(tableName);
return getSelf();
}
public T VALUES(String columns, String values) {
sql().columns.add(columns);
sql().values.add(values);
return getSelf();
}
public T SELECT(String columns) {
sql().statementType = SQLStatement.StatementType.SELECT;
sql().select.add(columns);
return getSelf();
}
public T SELECT_DISTINCT(String columns) {
sql().distinct = true;
SELECT(columns);
return getSelf();
}
public T DELETE_FROM(String table) {
sql().statementType = SQLStatement.StatementType.DELETE;
sql().tables.add(table);
return getSelf();
}
public T FROM(String table) {
sql().tables.add(table);
return getSelf();
}
public T JOIN(String join) {
sql().join.add(join);
return getSelf();
}
public T INNER_JOIN(String join) {
sql().innerJoin.add(join);
return getSelf();
}
public T LEFT_OUTER_JOIN(String join) {
sql().leftOuterJoin.add(join);
return getSelf();
}
public T RIGHT_OUTER_JOIN(String join) {
sql().rightOuterJoin.add(join);
return getSelf();
}
public T OUTER_JOIN(String join) {
sql().outerJoin.add(join);
return getSelf();
}
public T WHERE(String conditions) {
sql().where.add(conditions);
sql().lastList = sql().where;
return getSelf();
}
public T OR() {
sql().lastList.add(OR);
return getSelf();
}
public T AND() {
sql().lastList.add(AND);
return getSelf();
}
public T GROUP_BY(String columns) {
sql().groupBy.add(columns);
return getSelf();
}
public T HAVING(String conditions) {
sql().having.add(conditions);
sql().lastList = sql().having;
return getSelf();
}
public T ORDER_BY(String columns) {
sql().orderBy.add(columns);
return getSelf();
}
private SQLStatement sql = new SQLStatement();
private SQLStatement sql() {
return sql;
}
public <A extends Appendable> A usingAppender(A a) {
sql().sql(a);
return a;
}
@Override
public String toString() {
StringBuilder sb = new StringBuilder();
sql().sql(sb);
return sb.toString();
}
private static class SafeAppendable {
private final Appendable a;
private boolean empty = true;
public SafeAppendable(Appendable a) {
super();
this.a = a;
}
public SafeAppendable append(CharSequence s) {
try {
if (empty && s.length() > 0) empty = false;
a.append(s);
} catch (IOException e) {
throw new RuntimeException(e);
}
return this;
}
public boolean isEmpty() {
return empty;
}
}
private static class SQLStatement {
public enum StatementType {
DELETE, INSERT, SELECT, UPDATE
}
StatementType statementType;
List<String> sets = new ArrayList<String>();
List<String> select = new ArrayList<String>();
List<String> tables = new ArrayList<String>();
List<String> join = new ArrayList<String>();
List<String> innerJoin = new ArrayList<String>();
List<String> outerJoin = new ArrayList<String>();
List<String> leftOuterJoin = new ArrayList<String>();
List<String> rightOuterJoin = new ArrayList<String>();
List<String> where = new ArrayList<String>();
List<String> having = new ArrayList<String>();
List<String> groupBy = new ArrayList<String>();
List<String> orderBy = new ArrayList<String>();
List<String> lastList = new ArrayList<String>();
List<String> columns = new ArrayList<String>();
List<String> values = new ArrayList<String>();
boolean distinct;
private void sqlClause(SafeAppendable builder, String keyword, List<String> parts, String open, String close,
String conjunction) {
if (!parts.isEmpty()) {
if (!builder.isEmpty())
builder.append("\n");
builder.append(keyword);
builder.append(" ");
builder.append(open);
String last = "________";
for (int i = 0, n = parts.size(); i < n; i++) {
String part = parts.get(i);
if (i > 0 && !part.equals(AND) && !part.equals(OR) && !last.equals(AND) && !last.equals(OR)) {
builder.append(conjunction);
}
builder.append(part);
last = part;
}
builder.append(close);
}
}
private String selectSQL(SafeAppendable builder) {
if (distinct) {
sqlClause(builder, "SELECT DISTINCT", select, "", "", ", ");
} else {
sqlClause(builder, "SELECT", select, "", "", ", ");
}
sqlClause(builder, "FROM", tables, "", "", ", ");
sqlClause(builder, "JOIN", join, "", "", "\nJOIN ");
sqlClause(builder, "INNER JOIN", innerJoin, "", "", "\nINNER JOIN ");
sqlClause(builder, "OUTER JOIN", outerJoin, "", "", "\nOUTER JOIN ");
sqlClause(builder, "LEFT OUTER JOIN", leftOuterJoin, "", "", "\nLEFT OUTER JOIN ");
sqlClause(builder, "RIGHT OUTER JOIN", rightOuterJoin, "", "", "\nRIGHT OUTER JOIN ");
sqlClause(builder, "WHERE", where, "(", ")", " AND ");
sqlClause(builder, "GROUP BY", groupBy, "", "", ", ");
sqlClause(builder, "HAVING", having, "(", ")", " AND ");
sqlClause(builder, "ORDER BY", orderBy, "", "", ", ");
return builder.toString();
}
private String insertSQL(SafeAppendable builder) {
sqlClause(builder, "INSERT INTO", tables, "", "", "");
sqlClause(builder, "", columns, "(", ")", ", ");
sqlClause(builder, "VALUES", values, "(", ")", ", ");
return builder.toString();
}
private String deleteSQL(SafeAppendable builder) {
sqlClause(builder, "DELETE FROM", tables, "", "", "");
sqlClause(builder, "WHERE", where, "(", ")", " AND ");
return builder.toString();
}
private String updateSQL(SafeAppendable builder) {
sqlClause(builder, "UPDATE", tables, "", "", "");
sqlClause(builder, "SET", sets, "", "", ", ");
sqlClause(builder, "WHERE", where, "(", ")", " AND ");
return builder.toString();
}
public String sql(Appendable a) {
SafeAppendable builder = new SafeAppendable(a);
if (statementType == null) {
return null;
}
String answer;
switch (statementType) {
case DELETE:
answer = deleteSQL(builder);
break;
case INSERT:
answer = insertSQL(builder);
break;
case SELECT:
answer = selectSQL(builder);
break;
case UPDATE:
answer = updateSQL(builder);
break;
default:
answer = null;
}
return answer;
}
}
}
public class SQL extends AbstractSQL<SQL> {
@Override
public SQL getSelf() {
return this;
}
}