ParameterHandler接口是參數處理器，位於mybatis包的org.apache.ibatis.executor.parameter下，源碼如下：

1 public interface ParameterHandler {
2 
3 Object getParameterObject();//獲取參數
4 
5 void setParameters(PreparedStatement ps)//設置參數
6 throws SQLException;
7 
8 }

可見ParameterHandler接口只有簡單的兩個方法，一個是獲取參數一個是設置參數。ParameterHandler接口默認實現類是DefaultParameterHandler，主要源碼如下：

 1 public class DefaultParameterHandler implements ParameterHandler {
 2 
 3 private final TypeHandlerRegistry typeHandlerRegistry;
 4 
 5 private final MappedStatement mappedStatement;
 6 private final Object parameterObject;
 7 private BoundSql boundSql;
 8 private Configuration configuration;
 
 9 
10 public DefaultParameterHandler(MappedStatement mappedStatement, Object parameterObject, BoundSql boundSql) {
11 this.mappedStatement = mappedStatement;
12 this.configuration = mappedStatement.getConfiguration();
13 this.typeHandlerRegistry = mappedStatement.getConfiguration().getTypeHandlerRegistry();
 
14 this.parameterObject = parameterObject;//設置參數
15 this.boundSql = boundSql;
16 }
17 
18 @Override
19 public Object getParameterObject() {
20 return parameterObject;//返回參數
21 }
22 
23 @Override
24 public void setParameters(PreparedStatement ps) {
25 ErrorContext.instance().activity("setting parameters").object(mappedStatement.getParameterMap().getId());
26 List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();//獲取所有參數，ParameterMapping是jdbc和java類型之間的對應關系
27 if (parameterMappings != null) {
28 //遍歷所有參數，將java 類型設置成jdbc類型
29 for (int i = 0; i < parameterMappings.size(); i++) {
30 ParameterMapping parameterMapping = parameterMappings.get(i);
31 if (parameterMapping.getMode() != ParameterMode.OUT) {
32 Object value;
33 String propertyName = parameterMapping.getProperty();
34 if (boundSql.hasAdditionalParameter(propertyName)) { // issue #448 ask first for additional params
35 value = boundSql.getAdditionalParameter(propertyName);
36 } else if (parameterObject == null) {
37 value = null;
38 } else if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass())) {
39 value = parameterObject;
40 } else {
41 MetaObject metaObject = configuration.newMetaObject(parameterObject);
42 value = metaObject.getValue(propertyName);
43 }
44 TypeHandler typeHandler = parameterMapping.getTypeHandler();
45 JdbcType jdbcType = parameterMapping.getJdbcType();
46 if (value == null && jdbcType == null) {
47 jdbcType = configuration.getJdbcTypeForNull();
48 }
49 try {
50 typeHandler.setParameter(ps, i + 1, value, jdbcType);
51 } catch (TypeException e) {
52 throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + e, e);
53 } catch (SQLException e) {
54 throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + e, e);
55 }
56 }
57 }
58 }
59 }
60 
61 }

而ParameterHandler的初始化同樣也是在Configuration中實現的，代碼如下：

1   public ParameterHandler newParameterHandler(MappedStatement mappedStatement, Object parameterObject, BoundSql boundSql) {
2     ParameterHandler parameterHandler = mappedStatement.getLang().createParameterHandler(mappedStatement, parameterObject, boundSql);
3     parameterHandler = (ParameterHandler) interceptorChain.pluginAll(parameterHandler);
4     return parameterHandler;
5   }

mybatis源碼解析11---ParameterHandler解析