Question

如何解析Mybatis xml文件中配置的sql

Answer 1

首先抽象一个SQL语句类：

[java] view plain copy
public abstract class AbstractSQLStatementNode implements ISQLStatement {

protected List<ISQLStatement> sqlStatements = new ArrayList<>();

@Override
public void appendSQL(ISQLStatement sql) {
sqlStatements.add(sql);
}

@Override
public String getSQL(Object object) {
StringBuilder sb = new StringBuilder();
for (ISQLStatement stmt : sqlStatements) {
sb.append(stmt.getSQL(object));
}
return sb.toString().trim();
}

}

然后是文本SQL:

[java] view plain copy
public class PlainSQLNode extends AbstractSQLStatementNode {

private final String sql;

public PlainSQLNode(String sql) {
this.sql = sql;
}

@Override
public String getSQL(Object object) {
return sql;
}

@Override
public String toString() {
return sql;
}

}

以Mybatis xml中<if test="...">...</if>为例

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public class IfSQLNode extends AbstractSQLStatementNode {

private final String test;

public IfSQLNode(String test) {
this.test = test;
}

public String getTest() {
return test;
}

@Override
public String getSQL(Object object) {
try {
Boolean b = (Boolean) Ognl.getValue(test, object, Boolean.TYPE);
return b ? super.getSQL(object) : "";
}
catch (OgnlException e) {
throw new SQLSyntaxException(e);
}
}

}

再增加一个Include标签例

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public class IncludeSQLNode extends AbstractSQLStatementNode {

private final TableNode node;
private final String refid;

public IncludeSQLNode(TableNode node, String refid) {
this.node = node;
this.refid = refid;
}

@Override
public String getSQL(Object object) {
SQLNode sqlnode = node.getSQLNode(refid);
return sqlnode.getSQL(object);
}

}

其它的xml标签类似，完成最终的sql

调用AbstractSQLStatementNode.getSQL方法，参数为客户端传入参数

XML例子如下：

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<select id="findPage" parameterType="java.util.Map" resultMap="ORG">
SELECT * FROM XT_ORG WHERE BDELETE<>1 <if test="name != null"> AND NAME=#{name}</if> LIMIT #{OFFSET}, #{ROWS}
</select>

根据是否传入了name，即可成功执行出最终的sql

SELECT * FROM XT_ORG WHERE BDELETE<>1 AND NAME=#{name} LIMIT #{OFFSET}, #{ROWS}

再解析SQL得到，并提出参数

SELECT * FROM XT_ORG WHERE BDELETE<>1 AND NAME=? LIMIT ?,?
即可生成最终的PrepareStatement