請查看最新整理地址：http://leeyee.github.io/blog/2012/09/27/mybatis-param-mapping-rules
最近在*Mybatis*的學習中對於映射語句中的參數註釋設置有點犯迷糊，於是在*debug*下跟蹤了下源代碼，發現*Mybatis*在接口方法映射語句中會做如下處理：
1. 接口方法只有一個參數
1.1 不使用`@Param`註解
1.1.1 參數爲基本類型或爲基本包裝類型(int,Integer,String...)
參數註釋爲: #{任意字符}
1.1.2 參數爲自定義對象
參數註釋爲: #{對象屬性}
示例：
<span mce_style="font-size: medium;" style="font-size:14px; "> User getUserById(int id);
// 注：該中情況下'任意字符'不能爲空，否則報錯
// select * from <TABEL> where id = #{任意字符}
select * from <TABLE> where id = #{id}
User getUser(User user); // user.getName user.getAge
select * from <TABLE> where name = #{name} and age = #{age}</span>
1.2 使用`@Param`註解
1.2.1 參數爲基本類型或爲基本包裝類型(int,Integer,String...)
參數註釋爲: #{註解名稱} | #{param1}
1.2.2 參數爲自定義對象
參數註釋爲: #{註解名稱.對象屬性} | #{param1.對象屬性}
示例：
<span mce_style="font-size: medium;" style="font-size:14px; "> User getUserById(@Param(value="keyId") int id);
select * from <TABEL> where id = #{keyId}
// or
select * from <TABLE> where id = #{param1}
User getUser(@Param(value="usr") User user); // user.getName user.getAge
select * from <TABLE> where name = #{user.name} and age = #{user.age}
// or
select * from <TABLE> where name = #{param1.name} and age = #{param1.age}</span>
2. 接口方法有兩個及兩個以上參數
2.1 不使用`@Param`註解
2.1.1 參數爲基本類型或爲基本包裝類型(int,Integer,String...)
參數註釋爲: #{參數位置[0..n-1]} | #{param[1..n]}
2.1.2 參數爲自定義對象
參數註釋爲: #{參數位置[0..n-1].對象屬性} | #{param[1..n].對象屬性}
示例：
<span mce_style="font-size: medium;" style="font-size:14px; "> User getUser(String name, int age);
select * from <TABLE> where name = #{0} and age = #{1}
// or
select * from <TABLE> where name = #{param1} and age = #{param2}
User getUser(User usr, int flag);
select * from <TABLE> where name = #{0.name} and age = {0.age} and flag = #{1}
// or
select * from <TABLE> where name = #{param1.name} and age = {param1.age} and flag = #{param2}</span>
2.2 使用`@Param`註解
2.2.1 參數爲基本類型或爲基本包裝類型(int,Integer,String...)
參數註釋爲: #{註解名稱} | #{param[1..n]}
2.2.2 參數爲自定義對象
參數註釋爲: #{註解名稱.對象屬性} | #{param[1..n].對象屬性}
示例：
<span mce_style="font-size: medium;" style="font-size:14px; "> User getUser(@Param(value="xm") String name, @Param(value="nl") int age);
select * from <TABLE> where name = #{xm} and age = #{nl}
// or
select * from <TABLE> where name = #{param1} and age = #{param2}
// or
select * from <TABLE> where name = #{xm} and age = #{param2}
User getUser(@Param(value="usr") User user, @Param(value="tag") int flag);
select * from <TABLE> where name = #{usr.name} and age = #{usr.age} and flag = #{tag}
// or
select * from <TABLE> where name = #{param1.name} and age = #{param1.age} and flag = #{param2}
// or
select * from <TABLE> where name = #{usr.name} and age = #{param1.age} and flag = #{param2}</span>
2.2.3 部分參數使用`@Param`註解
當採用部分參數使用`@Param`註解時，參數註釋爲將以上兩種情況結合起來即可。
示例：
<span mce_style="font-size: medium;" style="font-size:14px; ">User getUser(String name, @Param(value="nl") age, int gendar);
// 對於age的訪問不能是 #{1} 只能是 #{param2} | #{nl}
select * from <TABLE> where name = #{0} and age = #{nl} and gendar = #{param3)</span>
總結下
- `@Param`的作用是設置參數別名。設置後的參數只能通過`#{param[1..n]`或者`#{註解別名}`來訪問
- 多個參數情況下，均可使用 `#{參數位置[0..n-1]}` | `#{param[1..n]}`來訪問參數
最後給出幾個源代碼中關於參數設置的源代碼供大家參考：
參數獲取操作：org.apache.ibatis.binding.MapperMethod.getParam(Object[] args)
<span mce_style="font-size: medium;" style="font-size:14px; "> private Object getParam(Object[] args) {
final int paramCount = paramPositions.size();
// 無參數
if (args == null || paramCount == 0) {
return null;
// 無註解並參數個數爲1
} else if (!hasNamedParameters && paramCount == 1) {
return args[paramPositions.get(0)];
} else {
Map<String, Object> param = new MapperParamMap<Object>();
for (int i = 0; i < paramCount; i++) {
param.put(paramNames.get(i), args[paramPositions.get(i)]);
}
// issue #71, add param names as param1, param2...but ensure backward compatibility
// 這就是 #{param[1..n]} 的來源
for (int i = 0; i < paramCount; i++) {
String genericParamName = "param" + String.valueOf(i + 1);
if (!param.containsKey(genericParamName)) {
param.put(genericParamName, args[paramPositions.get(i)]);
}
}
return param;
}
}</span>SQL預編譯參數設置：org.apache.ibatis.executor.parameter.DefaultParameterHandler.setParameters(PreparedStatement ps) throws SQLException
<span mce_style="font-size: medium;" style="font-size:14px; ">org.apache.ibatis.executor.parameter.DefaultParameterHandler.setParameters(PreparedStatement ps) throws SQLException
public void setParameters(PreparedStatement ps)
throws SQLException {
ErrorContext.instance().activity("setting parameters").object(mappedStatement.getParameterMap().getId());
List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
if (parameterMappings != null) {
MetaObject metaObject = parameterObject == null ? null : configuration.newMetaObject(parameterObject);
for (int i = 0; i < parameterMappings.size(); i++) {
ParameterMapping parameterMapping = parameterMappings.get(i);
if (parameterMapping.getMode() != ParameterMode.OUT) {
Object value;
String propertyName = parameterMapping.getProperty();
PropertyTokenizer prop = new PropertyTokenizer(propertyName);
if (parameterObject == null) {
value = null;
} else if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass())) {
value = parameterObject;
} else if (boundSql.hasAdditionalParameter(propertyName)) {
value = boundSql.getAdditionalParameter(propertyName);
} else if (propertyName.startsWith(ForEachSqlNode.ITEM_PREFIX)
&& boundSql.hasAdditionalParameter(prop.getName())) {
value = boundSql.getAdditionalParameter(prop.getName());
if (value != null) {
value = configuration.newMetaObject(value).getValue(propertyName.substring(prop.getName().length()));
}
} else {
value = metaObject == null ? null : metaObject.getValue(propertyName);
}
TypeHandler typeHandler = parameterMapping.getTypeHandler();
if (typeHandler == null) {
throw new ExecutorException("There was no TypeHandler found for parameter " + propertyName + " of statement " + mappedStatement.getId());
}
JdbcType jdbcType = parameterMapping.getJdbcType();
if (value == null && jdbcType == null) jdbcType = configuration.getJdbcTypeForNull();
typeHandler.setParameter(ps, i + 1, value, jdbcType);
}
}
}
}</span>